1 // Algorithm implementation -*- C++ -*-
2 
3 // Copyright (C) 2001-2018 Free Software Foundation, Inc.
4 //
5 // This file is part of the GNU ISO C++ Library.  This library is free
6 // software; you can redistribute it and/or modify it under the
7 // terms of the GNU General Public License as published by the
8 // Free Software Foundation; either version 3, or (at your option)
9 // any later version.
10 
11 // This library is distributed in the hope that it will be useful,
12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14 // GNU General Public License for more details.
15 
16 // Under Section 7 of GPL version 3, you are granted additional
17 // permissions described in the GCC Runtime Library Exception, version
18 // 3.1, as published by the Free Software Foundation.
19 
20 // You should have received a copy of the GNU General Public License and
21 // a copy of the GCC Runtime Library Exception along with this program;
22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23 // <http://www.gnu.org/licenses/>.
24 
25 /*
26  *
27  * Copyright (c) 1994
28  * Hewlett-Packard Company
29  *
30  * Permission to use, copy, modify, distribute and sell this software
31  * and its documentation for any purpose is hereby granted without fee,
32  * provided that the above copyright notice appear in all copies and
33  * that both that copyright notice and this permission notice appear
34  * in supporting documentation.  Hewlett-Packard Company makes no
35  * representations about the suitability of this software for any
36  * purpose.  It is provided "as is" without express or implied warranty.
37  *
38  *
39  * Copyright (c) 1996
40  * Silicon Graphics Computer Systems, Inc.
41  *
42  * Permission to use, copy, modify, distribute and sell this software
43  * and its documentation for any purpose is hereby granted without fee,
44  * provided that the above copyright notice appear in all copies and
45  * that both that copyright notice and this permission notice appear
46  * in supporting documentation.  Silicon Graphics makes no
47  * representations about the suitability of this software for any
48  * purpose.  It is provided "as is" without express or implied warranty.
49  */
50 
51 /** @file bits/stl_algo.h
52  *  This is an internal header file, included by other library headers.
53  *  Do not attempt to use it directly. @headername{algorithm}
54  */
55 
56 #ifndef _STL_ALGO_H
57 #define _STL_ALGO_H 1
58 
59 #include <cstdlib>	     // for rand
60 #include <bits/algorithmfwd.h>
61 #include <bits/stl_heap.h>
62 #include <bits/stl_tempbuf.h>  // for _Temporary_buffer
63 #include <bits/predefined_ops.h>
64 
65 #if __cplusplus >= 201103L
66 #include <bits/uniform_int_dist.h>
67 #endif
68 
69 // See concept_check.h for the __glibcxx_*_requires macros.
70 
71 namespace std _GLIBCXX_VISIBILITY(default)
72 {
73 _GLIBCXX_BEGIN_NAMESPACE_VERSION
74 
75   /// Swaps the median value of *__a, *__b and *__c under __comp to *__result
76   template<typename _Iterator, typename _Compare>
77     void
78     __move_median_to_first(_Iterator __result,_Iterator __a, _Iterator __b,
79 			   _Iterator __c, _Compare __comp)
80     {
81       if (__comp(__a, __b))
82 	{
83 	  if (__comp(__b, __c))
84 	    std::iter_swap(__result, __b);
85 	  else if (__comp(__a, __c))
86 	    std::iter_swap(__result, __c);
87 	  else
88 	    std::iter_swap(__result, __a);
89 	}
90       else if (__comp(__a, __c))
91 	std::iter_swap(__result, __a);
92       else if (__comp(__b, __c))
93 	std::iter_swap(__result, __c);
94       else
95 	std::iter_swap(__result, __b);
96     }
97 
98   /// This is an overload used by find algos for the Input Iterator case.
99   template<typename _InputIterator, typename _Predicate>
100     inline _InputIterator
101     __find_if(_InputIterator __first, _InputIterator __last,
102 	      _Predicate __pred, input_iterator_tag)
103     {
104       while (__first != __last && !__pred(__first))
105 	++__first;
106       return __first;
107     }
108 
109   /// This is an overload used by find algos for the RAI case.
110   template<typename _RandomAccessIterator, typename _Predicate>
111     _RandomAccessIterator
112     __find_if(_RandomAccessIterator __first, _RandomAccessIterator __last,
113 	      _Predicate __pred, random_access_iterator_tag)
114     {
115       typename iterator_traits<_RandomAccessIterator>::difference_type
116 	__trip_count = (__last - __first) >> 2;
117 
118       for (; __trip_count > 0; --__trip_count)
119 	{
120 	  if (__pred(__first))
121 	    return __first;
122 	  ++__first;
123 
124 	  if (__pred(__first))
125 	    return __first;
126 	  ++__first;
127 
128 	  if (__pred(__first))
129 	    return __first;
130 	  ++__first;
131 
132 	  if (__pred(__first))
133 	    return __first;
134 	  ++__first;
135 	}
136 
137       switch (__last - __first)
138 	{
139 	case 3:
140 	  if (__pred(__first))
141 	    return __first;
142 	  ++__first;
143 	case 2:
144 	  if (__pred(__first))
145 	    return __first;
146 	  ++__first;
147 	case 1:
148 	  if (__pred(__first))
149 	    return __first;
150 	  ++__first;
151 	case 0:
152 	default:
153 	  return __last;
154 	}
155     }
156 
157   template<typename _Iterator, typename _Predicate>
158     inline _Iterator
159     __find_if(_Iterator __first, _Iterator __last, _Predicate __pred)
160     {
161       return __find_if(__first, __last, __pred,
162 		       std::__iterator_category(__first));
163     }
164 
165   /// Provided for stable_partition to use.
166   template<typename _InputIterator, typename _Predicate>
167     inline _InputIterator
168     __find_if_not(_InputIterator __first, _InputIterator __last,
169 		  _Predicate __pred)
170     {
171       return std::__find_if(__first, __last,
172 			    __gnu_cxx::__ops::__negate(__pred),
173 			    std::__iterator_category(__first));
174     }
175 
176   /// Like find_if_not(), but uses and updates a count of the
177   /// remaining range length instead of comparing against an end
178   /// iterator.
179   template<typename _InputIterator, typename _Predicate, typename _Distance>
180     _InputIterator
181     __find_if_not_n(_InputIterator __first, _Distance& __len, _Predicate __pred)
182     {
183       for (; __len; --__len,  (void) ++__first)
184 	if (!__pred(__first))
185 	  break;
186       return __first;
187     }
188 
189   // set_difference
190   // set_intersection
191   // set_symmetric_difference
192   // set_union
193   // for_each
194   // find
195   // find_if
196   // find_first_of
197   // adjacent_find
198   // count
199   // count_if
200   // search
201 
202   template<typename _ForwardIterator1, typename _ForwardIterator2,
203 	   typename _BinaryPredicate>
204     _ForwardIterator1
205     __search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
206 	     _ForwardIterator2 __first2, _ForwardIterator2 __last2,
207 	     _BinaryPredicate  __predicate)
208     {
209       // Test for empty ranges
210       if (__first1 == __last1 || __first2 == __last2)
211 	return __first1;
212 
213       // Test for a pattern of length 1.
214       _ForwardIterator2 __p1(__first2);
215       if (++__p1 == __last2)
216 	return std::__find_if(__first1, __last1,
217 		__gnu_cxx::__ops::__iter_comp_iter(__predicate, __first2));
218 
219       // General case.
220       _ForwardIterator2 __p;
221       _ForwardIterator1 __current = __first1;
222 
223       for (;;)
224 	{
225 	  __first1 =
226 	    std::__find_if(__first1, __last1,
227 		__gnu_cxx::__ops::__iter_comp_iter(__predicate, __first2));
228 
229 	  if (__first1 == __last1)
230 	    return __last1;
231 
232 	  __p = __p1;
233 	  __current = __first1;
234 	  if (++__current == __last1)
235 	    return __last1;
236 
237 	  while (__predicate(__current, __p))
238 	    {
239 	      if (++__p == __last2)
240 		return __first1;
241 	      if (++__current == __last1)
242 		return __last1;
243 	    }
244 	  ++__first1;
245 	}
246       return __first1;
247     }
248 
249   // search_n
250 
251   /**
252    *  This is an helper function for search_n overloaded for forward iterators.
253   */
254   template<typename _ForwardIterator, typename _Integer,
255 	   typename _UnaryPredicate>
256     _ForwardIterator
257     __search_n_aux(_ForwardIterator __first, _ForwardIterator __last,
258 		   _Integer __count, _UnaryPredicate __unary_pred,
259 		   std::forward_iterator_tag)
260     {
261       __first = std::__find_if(__first, __last, __unary_pred);
262       while (__first != __last)
263 	{
264 	  typename iterator_traits<_ForwardIterator>::difference_type
265 	    __n = __count;
266 	  _ForwardIterator __i = __first;
267 	  ++__i;
268 	  while (__i != __last && __n != 1 && __unary_pred(__i))
269 	    {
270 	      ++__i;
271 	      --__n;
272 	    }
273 	  if (__n == 1)
274 	    return __first;
275 	  if (__i == __last)
276 	    return __last;
277 	  __first = std::__find_if(++__i, __last, __unary_pred);
278 	}
279       return __last;
280     }
281 
282   /**
283    *  This is an helper function for search_n overloaded for random access
284    *  iterators.
285   */
286   template<typename _RandomAccessIter, typename _Integer,
287 	   typename _UnaryPredicate>
288     _RandomAccessIter
289     __search_n_aux(_RandomAccessIter __first, _RandomAccessIter __last,
290 		   _Integer __count, _UnaryPredicate __unary_pred,
291 		   std::random_access_iterator_tag)
292     {
293       typedef typename std::iterator_traits<_RandomAccessIter>::difference_type
294 	_DistanceType;
295 
296       _DistanceType __tailSize = __last - __first;
297       _DistanceType __remainder = __count;
298 
299       while (__remainder <= __tailSize) // the main loop...
300 	{
301 	  __first += __remainder;
302 	  __tailSize -= __remainder;
303 	  // __first here is always pointing to one past the last element of
304 	  // next possible match.
305 	  _RandomAccessIter __backTrack = __first;
306 	  while (__unary_pred(--__backTrack))
307 	    {
308 	      if (--__remainder == 0)
309 		return (__first - __count); // Success
310 	    }
311 	  __remainder = __count + 1 - (__first - __backTrack);
312 	}
313       return __last; // Failure
314     }
315 
316   template<typename _ForwardIterator, typename _Integer,
317 	   typename _UnaryPredicate>
318     _ForwardIterator
319     __search_n(_ForwardIterator __first, _ForwardIterator __last,
320 	       _Integer __count,
321 	       _UnaryPredicate __unary_pred)
322     {
323       if (__count <= 0)
324 	return __first;
325 
326       if (__count == 1)
327 	return std::__find_if(__first, __last, __unary_pred);
328 
329       return std::__search_n_aux(__first, __last, __count, __unary_pred,
330 				 std::__iterator_category(__first));
331     }
332 
333   // find_end for forward iterators.
334   template<typename _ForwardIterator1, typename _ForwardIterator2,
335 	   typename _BinaryPredicate>
336     _ForwardIterator1
337     __find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
338 	       _ForwardIterator2 __first2, _ForwardIterator2 __last2,
339 	       forward_iterator_tag, forward_iterator_tag,
340 	       _BinaryPredicate __comp)
341     {
342       if (__first2 == __last2)
343 	return __last1;
344 
345       _ForwardIterator1 __result = __last1;
346       while (1)
347 	{
348 	  _ForwardIterator1 __new_result
349 	    = std::__search(__first1, __last1, __first2, __last2, __comp);
350 	  if (__new_result == __last1)
351 	    return __result;
352 	  else
353 	    {
354 	      __result = __new_result;
355 	      __first1 = __new_result;
356 	      ++__first1;
357 	    }
358 	}
359     }
360 
361   // find_end for bidirectional iterators (much faster).
362   template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
363 	   typename _BinaryPredicate>
364     _BidirectionalIterator1
365     __find_end(_BidirectionalIterator1 __first1,
366 	       _BidirectionalIterator1 __last1,
367 	       _BidirectionalIterator2 __first2,
368 	       _BidirectionalIterator2 __last2,
369 	       bidirectional_iterator_tag, bidirectional_iterator_tag,
370 	       _BinaryPredicate __comp)
371     {
372       // concept requirements
373       __glibcxx_function_requires(_BidirectionalIteratorConcept<
374 				  _BidirectionalIterator1>)
375       __glibcxx_function_requires(_BidirectionalIteratorConcept<
376 				  _BidirectionalIterator2>)
377 
378       typedef reverse_iterator<_BidirectionalIterator1> _RevIterator1;
379       typedef reverse_iterator<_BidirectionalIterator2> _RevIterator2;
380 
381       _RevIterator1 __rlast1(__first1);
382       _RevIterator2 __rlast2(__first2);
383       _RevIterator1 __rresult = std::__search(_RevIterator1(__last1), __rlast1,
384 					      _RevIterator2(__last2), __rlast2,
385 					      __comp);
386 
387       if (__rresult == __rlast1)
388 	return __last1;
389       else
390 	{
391 	  _BidirectionalIterator1 __result = __rresult.base();
392 	  std::advance(__result, -std::distance(__first2, __last2));
393 	  return __result;
394 	}
395     }
396 
397   /**
398    *  @brief  Find last matching subsequence in a sequence.
399    *  @ingroup non_mutating_algorithms
400    *  @param  __first1  Start of range to search.
401    *  @param  __last1   End of range to search.
402    *  @param  __first2  Start of sequence to match.
403    *  @param  __last2   End of sequence to match.
404    *  @return   The last iterator @c i in the range
405    *  @p [__first1,__last1-(__last2-__first2)) such that @c *(i+N) ==
406    *  @p *(__first2+N) for each @c N in the range @p
407    *  [0,__last2-__first2), or @p __last1 if no such iterator exists.
408    *
409    *  Searches the range @p [__first1,__last1) for a sub-sequence that
410    *  compares equal value-by-value with the sequence given by @p
411    *  [__first2,__last2) and returns an iterator to the __first
412    *  element of the sub-sequence, or @p __last1 if the sub-sequence
413    *  is not found.  The sub-sequence will be the last such
414    *  subsequence contained in [__first1,__last1).
415    *
416    *  Because the sub-sequence must lie completely within the range @p
417    *  [__first1,__last1) it must start at a position less than @p
418    *  __last1-(__last2-__first2) where @p __last2-__first2 is the
419    *  length of the sub-sequence.  This means that the returned
420    *  iterator @c i will be in the range @p
421    *  [__first1,__last1-(__last2-__first2))
422   */
423   template<typename _ForwardIterator1, typename _ForwardIterator2>
424     inline _ForwardIterator1
425     find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
426 	     _ForwardIterator2 __first2, _ForwardIterator2 __last2)
427     {
428       // concept requirements
429       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
430       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
431       __glibcxx_function_requires(_EqualOpConcept<
432 	    typename iterator_traits<_ForwardIterator1>::value_type,
433 	    typename iterator_traits<_ForwardIterator2>::value_type>)
434       __glibcxx_requires_valid_range(__first1, __last1);
435       __glibcxx_requires_valid_range(__first2, __last2);
436 
437       return std::__find_end(__first1, __last1, __first2, __last2,
438 			     std::__iterator_category(__first1),
439 			     std::__iterator_category(__first2),
440 			     __gnu_cxx::__ops::__iter_equal_to_iter());
441     }
442 
443   /**
444    *  @brief  Find last matching subsequence in a sequence using a predicate.
445    *  @ingroup non_mutating_algorithms
446    *  @param  __first1  Start of range to search.
447    *  @param  __last1   End of range to search.
448    *  @param  __first2  Start of sequence to match.
449    *  @param  __last2   End of sequence to match.
450    *  @param  __comp    The predicate to use.
451    *  @return The last iterator @c i in the range @p
452    *  [__first1,__last1-(__last2-__first2)) such that @c
453    *  predicate(*(i+N), @p (__first2+N)) is true for each @c N in the
454    *  range @p [0,__last2-__first2), or @p __last1 if no such iterator
455    *  exists.
456    *
457    *  Searches the range @p [__first1,__last1) for a sub-sequence that
458    *  compares equal value-by-value with the sequence given by @p
459    *  [__first2,__last2) using comp as a predicate and returns an
460    *  iterator to the first element of the sub-sequence, or @p __last1
461    *  if the sub-sequence is not found.  The sub-sequence will be the
462    *  last such subsequence contained in [__first,__last1).
463    *
464    *  Because the sub-sequence must lie completely within the range @p
465    *  [__first1,__last1) it must start at a position less than @p
466    *  __last1-(__last2-__first2) where @p __last2-__first2 is the
467    *  length of the sub-sequence.  This means that the returned
468    *  iterator @c i will be in the range @p
469    *  [__first1,__last1-(__last2-__first2))
470   */
471   template<typename _ForwardIterator1, typename _ForwardIterator2,
472 	   typename _BinaryPredicate>
473     inline _ForwardIterator1
474     find_end(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
475 	     _ForwardIterator2 __first2, _ForwardIterator2 __last2,
476 	     _BinaryPredicate __comp)
477     {
478       // concept requirements
479       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
480       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
481       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
482 	    typename iterator_traits<_ForwardIterator1>::value_type,
483 	    typename iterator_traits<_ForwardIterator2>::value_type>)
484       __glibcxx_requires_valid_range(__first1, __last1);
485       __glibcxx_requires_valid_range(__first2, __last2);
486 
487       return std::__find_end(__first1, __last1, __first2, __last2,
488 			     std::__iterator_category(__first1),
489 			     std::__iterator_category(__first2),
490 			     __gnu_cxx::__ops::__iter_comp_iter(__comp));
491     }
492 
493 #if __cplusplus >= 201103L
494   /**
495    *  @brief  Checks that a predicate is true for all the elements
496    *          of a sequence.
497    *  @ingroup non_mutating_algorithms
498    *  @param  __first   An input iterator.
499    *  @param  __last    An input iterator.
500    *  @param  __pred    A predicate.
501    *  @return  True if the check is true, false otherwise.
502    *
503    *  Returns true if @p __pred is true for each element in the range
504    *  @p [__first,__last), and false otherwise.
505   */
506   template<typename _InputIterator, typename _Predicate>
507     inline bool
508     all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
509     { return __last == std::find_if_not(__first, __last, __pred); }
510 
511   /**
512    *  @brief  Checks that a predicate is false for all the elements
513    *          of a sequence.
514    *  @ingroup non_mutating_algorithms
515    *  @param  __first   An input iterator.
516    *  @param  __last    An input iterator.
517    *  @param  __pred    A predicate.
518    *  @return  True if the check is true, false otherwise.
519    *
520    *  Returns true if @p __pred is false for each element in the range
521    *  @p [__first,__last), and false otherwise.
522   */
523   template<typename _InputIterator, typename _Predicate>
524     inline bool
525     none_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
526     { return __last == _GLIBCXX_STD_A::find_if(__first, __last, __pred); }
527 
528   /**
529    *  @brief  Checks that a predicate is false for at least an element
530    *          of a sequence.
531    *  @ingroup non_mutating_algorithms
532    *  @param  __first   An input iterator.
533    *  @param  __last    An input iterator.
534    *  @param  __pred    A predicate.
535    *  @return  True if the check is true, false otherwise.
536    *
537    *  Returns true if an element exists in the range @p
538    *  [__first,__last) such that @p __pred is true, and false
539    *  otherwise.
540   */
541   template<typename _InputIterator, typename _Predicate>
542     inline bool
543     any_of(_InputIterator __first, _InputIterator __last, _Predicate __pred)
544     { return !std::none_of(__first, __last, __pred); }
545 
546   /**
547    *  @brief  Find the first element in a sequence for which a
548    *          predicate is false.
549    *  @ingroup non_mutating_algorithms
550    *  @param  __first  An input iterator.
551    *  @param  __last   An input iterator.
552    *  @param  __pred   A predicate.
553    *  @return   The first iterator @c i in the range @p [__first,__last)
554    *  such that @p __pred(*i) is false, or @p __last if no such iterator exists.
555   */
556   template<typename _InputIterator, typename _Predicate>
557     inline _InputIterator
558     find_if_not(_InputIterator __first, _InputIterator __last,
559 		_Predicate __pred)
560     {
561       // concept requirements
562       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
563       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
564 	      typename iterator_traits<_InputIterator>::value_type>)
565       __glibcxx_requires_valid_range(__first, __last);
566       return std::__find_if_not(__first, __last,
567 				__gnu_cxx::__ops::__pred_iter(__pred));
568     }
569 
570   /**
571    *  @brief  Checks whether the sequence is partitioned.
572    *  @ingroup mutating_algorithms
573    *  @param  __first  An input iterator.
574    *  @param  __last   An input iterator.
575    *  @param  __pred   A predicate.
576    *  @return  True if the range @p [__first,__last) is partioned by @p __pred,
577    *  i.e. if all elements that satisfy @p __pred appear before those that
578    *  do not.
579   */
580   template<typename _InputIterator, typename _Predicate>
581     inline bool
582     is_partitioned(_InputIterator __first, _InputIterator __last,
583 		   _Predicate __pred)
584     {
585       __first = std::find_if_not(__first, __last, __pred);
586       if (__first == __last)
587 	return true;
588       ++__first;
589       return std::none_of(__first, __last, __pred);
590     }
591 
592   /**
593    *  @brief  Find the partition point of a partitioned range.
594    *  @ingroup mutating_algorithms
595    *  @param  __first   An iterator.
596    *  @param  __last    Another iterator.
597    *  @param  __pred    A predicate.
598    *  @return  An iterator @p mid such that @p all_of(__first, mid, __pred)
599    *           and @p none_of(mid, __last, __pred) are both true.
600   */
601   template<typename _ForwardIterator, typename _Predicate>
602     _ForwardIterator
603     partition_point(_ForwardIterator __first, _ForwardIterator __last,
604 		    _Predicate __pred)
605     {
606       // concept requirements
607       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
608       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
609 	      typename iterator_traits<_ForwardIterator>::value_type>)
610 
611       // A specific debug-mode test will be necessary...
612       __glibcxx_requires_valid_range(__first, __last);
613 
614       typedef typename iterator_traits<_ForwardIterator>::difference_type
615 	_DistanceType;
616 
617       _DistanceType __len = std::distance(__first, __last);
618       _DistanceType __half;
619       _ForwardIterator __middle;
620 
621       while (__len > 0)
622 	{
623 	  __half = __len >> 1;
624 	  __middle = __first;
625 	  std::advance(__middle, __half);
626 	  if (__pred(*__middle))
627 	    {
628 	      __first = __middle;
629 	      ++__first;
630 	      __len = __len - __half - 1;
631 	    }
632 	  else
633 	    __len = __half;
634 	}
635       return __first;
636     }
637 #endif
638 
639   template<typename _InputIterator, typename _OutputIterator,
640 	   typename _Predicate>
641     _OutputIterator
642     __remove_copy_if(_InputIterator __first, _InputIterator __last,
643 		     _OutputIterator __result, _Predicate __pred)
644     {
645       for (; __first != __last; ++__first)
646 	if (!__pred(__first))
647 	  {
648 	    *__result = *__first;
649 	    ++__result;
650 	  }
651       return __result;
652     }
653 
654   /**
655    *  @brief Copy a sequence, removing elements of a given value.
656    *  @ingroup mutating_algorithms
657    *  @param  __first   An input iterator.
658    *  @param  __last    An input iterator.
659    *  @param  __result  An output iterator.
660    *  @param  __value   The value to be removed.
661    *  @return   An iterator designating the end of the resulting sequence.
662    *
663    *  Copies each element in the range @p [__first,__last) not equal
664    *  to @p __value to the range beginning at @p __result.
665    *  remove_copy() is stable, so the relative order of elements that
666    *  are copied is unchanged.
667   */
668   template<typename _InputIterator, typename _OutputIterator, typename _Tp>
669     inline _OutputIterator
670     remove_copy(_InputIterator __first, _InputIterator __last,
671 		_OutputIterator __result, const _Tp& __value)
672     {
673       // concept requirements
674       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
675       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
676 	    typename iterator_traits<_InputIterator>::value_type>)
677       __glibcxx_function_requires(_EqualOpConcept<
678 	    typename iterator_traits<_InputIterator>::value_type, _Tp>)
679       __glibcxx_requires_valid_range(__first, __last);
680 
681       return std::__remove_copy_if(__first, __last, __result,
682 	__gnu_cxx::__ops::__iter_equals_val(__value));
683     }
684 
685   /**
686    *  @brief Copy a sequence, removing elements for which a predicate is true.
687    *  @ingroup mutating_algorithms
688    *  @param  __first   An input iterator.
689    *  @param  __last    An input iterator.
690    *  @param  __result  An output iterator.
691    *  @param  __pred    A predicate.
692    *  @return   An iterator designating the end of the resulting sequence.
693    *
694    *  Copies each element in the range @p [__first,__last) for which
695    *  @p __pred returns false to the range beginning at @p __result.
696    *
697    *  remove_copy_if() is stable, so the relative order of elements that are
698    *  copied is unchanged.
699   */
700   template<typename _InputIterator, typename _OutputIterator,
701 	   typename _Predicate>
702     inline _OutputIterator
703     remove_copy_if(_InputIterator __first, _InputIterator __last,
704 		   _OutputIterator __result, _Predicate __pred)
705     {
706       // concept requirements
707       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
708       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
709 	    typename iterator_traits<_InputIterator>::value_type>)
710       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
711 	    typename iterator_traits<_InputIterator>::value_type>)
712       __glibcxx_requires_valid_range(__first, __last);
713 
714       return std::__remove_copy_if(__first, __last, __result,
715 				   __gnu_cxx::__ops::__pred_iter(__pred));
716     }
717 
718 #if __cplusplus >= 201103L
719   /**
720    *  @brief Copy the elements of a sequence for which a predicate is true.
721    *  @ingroup mutating_algorithms
722    *  @param  __first   An input iterator.
723    *  @param  __last    An input iterator.
724    *  @param  __result  An output iterator.
725    *  @param  __pred    A predicate.
726    *  @return   An iterator designating the end of the resulting sequence.
727    *
728    *  Copies each element in the range @p [__first,__last) for which
729    *  @p __pred returns true to the range beginning at @p __result.
730    *
731    *  copy_if() is stable, so the relative order of elements that are
732    *  copied is unchanged.
733   */
734   template<typename _InputIterator, typename _OutputIterator,
735 	   typename _Predicate>
736     _OutputIterator
737     copy_if(_InputIterator __first, _InputIterator __last,
738 	    _OutputIterator __result, _Predicate __pred)
739     {
740       // concept requirements
741       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
742       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
743 	    typename iterator_traits<_InputIterator>::value_type>)
744       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
745 	    typename iterator_traits<_InputIterator>::value_type>)
746       __glibcxx_requires_valid_range(__first, __last);
747 
748       for (; __first != __last; ++__first)
749 	if (__pred(*__first))
750 	  {
751 	    *__result = *__first;
752 	    ++__result;
753 	  }
754       return __result;
755     }
756 
757   template<typename _InputIterator, typename _Size, typename _OutputIterator>
758     _OutputIterator
759     __copy_n(_InputIterator __first, _Size __n,
760 	     _OutputIterator __result, input_iterator_tag)
761     {
762       if (__n > 0)
763 	{
764 	  while (true)
765 	    {
766 	      *__result = *__first;
767 	      ++__result;
768 	      if (--__n > 0)
769 		++__first;
770 	      else
771 		break;
772 	    }
773 	}
774       return __result;
775     }
776 
777   template<typename _RandomAccessIterator, typename _Size,
778 	   typename _OutputIterator>
779     inline _OutputIterator
780     __copy_n(_RandomAccessIterator __first, _Size __n,
781 	     _OutputIterator __result, random_access_iterator_tag)
782     { return std::copy(__first, __first + __n, __result); }
783 
784   /**
785    *  @brief Copies the range [first,first+n) into [result,result+n).
786    *  @ingroup mutating_algorithms
787    *  @param  __first  An input iterator.
788    *  @param  __n      The number of elements to copy.
789    *  @param  __result An output iterator.
790    *  @return  result+n.
791    *
792    *  This inline function will boil down to a call to @c memmove whenever
793    *  possible.  Failing that, if random access iterators are passed, then the
794    *  loop count will be known (and therefore a candidate for compiler
795    *  optimizations such as unrolling).
796   */
797   template<typename _InputIterator, typename _Size, typename _OutputIterator>
798     inline _OutputIterator
799     copy_n(_InputIterator __first, _Size __n, _OutputIterator __result)
800     {
801       // concept requirements
802       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
803       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
804 	    typename iterator_traits<_InputIterator>::value_type>)
805 
806       return std::__copy_n(__first, __n, __result,
807 			   std::__iterator_category(__first));
808     }
809 
810   /**
811    *  @brief Copy the elements of a sequence to separate output sequences
812    *         depending on the truth value of a predicate.
813    *  @ingroup mutating_algorithms
814    *  @param  __first   An input iterator.
815    *  @param  __last    An input iterator.
816    *  @param  __out_true   An output iterator.
817    *  @param  __out_false  An output iterator.
818    *  @param  __pred    A predicate.
819    *  @return   A pair designating the ends of the resulting sequences.
820    *
821    *  Copies each element in the range @p [__first,__last) for which
822    *  @p __pred returns true to the range beginning at @p out_true
823    *  and each element for which @p __pred returns false to @p __out_false.
824   */
825   template<typename _InputIterator, typename _OutputIterator1,
826 	   typename _OutputIterator2, typename _Predicate>
827     pair<_OutputIterator1, _OutputIterator2>
828     partition_copy(_InputIterator __first, _InputIterator __last,
829 		   _OutputIterator1 __out_true, _OutputIterator2 __out_false,
830 		   _Predicate __pred)
831     {
832       // concept requirements
833       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
834       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator1,
835 	    typename iterator_traits<_InputIterator>::value_type>)
836       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator2,
837 	    typename iterator_traits<_InputIterator>::value_type>)
838       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
839 	    typename iterator_traits<_InputIterator>::value_type>)
840       __glibcxx_requires_valid_range(__first, __last);
841 
842       for (; __first != __last; ++__first)
843 	if (__pred(*__first))
844 	  {
845 	    *__out_true = *__first;
846 	    ++__out_true;
847 	  }
848 	else
849 	  {
850 	    *__out_false = *__first;
851 	    ++__out_false;
852 	  }
853 
854       return pair<_OutputIterator1, _OutputIterator2>(__out_true, __out_false);
855     }
856 #endif
857 
858   template<typename _ForwardIterator, typename _Predicate>
859     _ForwardIterator
860     __remove_if(_ForwardIterator __first, _ForwardIterator __last,
861 		_Predicate __pred)
862     {
863       __first = std::__find_if(__first, __last, __pred);
864       if (__first == __last)
865 	return __first;
866       _ForwardIterator __result = __first;
867       ++__first;
868       for (; __first != __last; ++__first)
869 	if (!__pred(__first))
870 	  {
871 	    *__result = _GLIBCXX_MOVE(*__first);
872 	    ++__result;
873 	  }
874       return __result;
875     }
876 
877   /**
878    *  @brief Remove elements from a sequence.
879    *  @ingroup mutating_algorithms
880    *  @param  __first  An input iterator.
881    *  @param  __last   An input iterator.
882    *  @param  __value  The value to be removed.
883    *  @return   An iterator designating the end of the resulting sequence.
884    *
885    *  All elements equal to @p __value are removed from the range
886    *  @p [__first,__last).
887    *
888    *  remove() is stable, so the relative order of elements that are
889    *  not removed is unchanged.
890    *
891    *  Elements between the end of the resulting sequence and @p __last
892    *  are still present, but their value is unspecified.
893   */
894   template<typename _ForwardIterator, typename _Tp>
895     inline _ForwardIterator
896     remove(_ForwardIterator __first, _ForwardIterator __last,
897 	   const _Tp& __value)
898     {
899       // concept requirements
900       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
901 				  _ForwardIterator>)
902       __glibcxx_function_requires(_EqualOpConcept<
903 	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
904       __glibcxx_requires_valid_range(__first, __last);
905 
906       return std::__remove_if(__first, __last,
907 		__gnu_cxx::__ops::__iter_equals_val(__value));
908     }
909 
910   /**
911    *  @brief Remove elements from a sequence using a predicate.
912    *  @ingroup mutating_algorithms
913    *  @param  __first  A forward iterator.
914    *  @param  __last   A forward iterator.
915    *  @param  __pred   A predicate.
916    *  @return   An iterator designating the end of the resulting sequence.
917    *
918    *  All elements for which @p __pred returns true are removed from the range
919    *  @p [__first,__last).
920    *
921    *  remove_if() is stable, so the relative order of elements that are
922    *  not removed is unchanged.
923    *
924    *  Elements between the end of the resulting sequence and @p __last
925    *  are still present, but their value is unspecified.
926   */
927   template<typename _ForwardIterator, typename _Predicate>
928     inline _ForwardIterator
929     remove_if(_ForwardIterator __first, _ForwardIterator __last,
930 	      _Predicate __pred)
931     {
932       // concept requirements
933       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
934 				  _ForwardIterator>)
935       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
936 	    typename iterator_traits<_ForwardIterator>::value_type>)
937       __glibcxx_requires_valid_range(__first, __last);
938 
939       return std::__remove_if(__first, __last,
940 			      __gnu_cxx::__ops::__pred_iter(__pred));
941     }
942 
943   template<typename _ForwardIterator, typename _BinaryPredicate>
944     _ForwardIterator
945     __adjacent_find(_ForwardIterator __first, _ForwardIterator __last,
946 		    _BinaryPredicate __binary_pred)
947     {
948       if (__first == __last)
949 	return __last;
950       _ForwardIterator __next = __first;
951       while (++__next != __last)
952 	{
953 	  if (__binary_pred(__first, __next))
954 	    return __first;
955 	  __first = __next;
956 	}
957       return __last;
958     }
959 
960   template<typename _ForwardIterator, typename _BinaryPredicate>
961     _ForwardIterator
962     __unique(_ForwardIterator __first, _ForwardIterator __last,
963 	     _BinaryPredicate __binary_pred)
964     {
965       // Skip the beginning, if already unique.
966       __first = std::__adjacent_find(__first, __last, __binary_pred);
967       if (__first == __last)
968 	return __last;
969 
970       // Do the real copy work.
971       _ForwardIterator __dest = __first;
972       ++__first;
973       while (++__first != __last)
974 	if (!__binary_pred(__dest, __first))
975 	  *++__dest = _GLIBCXX_MOVE(*__first);
976       return ++__dest;
977     }
978 
979   /**
980    *  @brief Remove consecutive duplicate values from a sequence.
981    *  @ingroup mutating_algorithms
982    *  @param  __first  A forward iterator.
983    *  @param  __last   A forward iterator.
984    *  @return  An iterator designating the end of the resulting sequence.
985    *
986    *  Removes all but the first element from each group of consecutive
987    *  values that compare equal.
988    *  unique() is stable, so the relative order of elements that are
989    *  not removed is unchanged.
990    *  Elements between the end of the resulting sequence and @p __last
991    *  are still present, but their value is unspecified.
992   */
993   template<typename _ForwardIterator>
994     inline _ForwardIterator
995     unique(_ForwardIterator __first, _ForwardIterator __last)
996     {
997       // concept requirements
998       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
999 				  _ForwardIterator>)
1000       __glibcxx_function_requires(_EqualityComparableConcept<
1001 		     typename iterator_traits<_ForwardIterator>::value_type>)
1002       __glibcxx_requires_valid_range(__first, __last);
1003 
1004       return std::__unique(__first, __last,
1005 			   __gnu_cxx::__ops::__iter_equal_to_iter());
1006     }
1007 
1008   /**
1009    *  @brief Remove consecutive values from a sequence using a predicate.
1010    *  @ingroup mutating_algorithms
1011    *  @param  __first        A forward iterator.
1012    *  @param  __last         A forward iterator.
1013    *  @param  __binary_pred  A binary predicate.
1014    *  @return  An iterator designating the end of the resulting sequence.
1015    *
1016    *  Removes all but the first element from each group of consecutive
1017    *  values for which @p __binary_pred returns true.
1018    *  unique() is stable, so the relative order of elements that are
1019    *  not removed is unchanged.
1020    *  Elements between the end of the resulting sequence and @p __last
1021    *  are still present, but their value is unspecified.
1022   */
1023   template<typename _ForwardIterator, typename _BinaryPredicate>
1024     inline _ForwardIterator
1025     unique(_ForwardIterator __first, _ForwardIterator __last,
1026 	   _BinaryPredicate __binary_pred)
1027     {
1028       // concept requirements
1029       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
1030 				  _ForwardIterator>)
1031       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
1032 		typename iterator_traits<_ForwardIterator>::value_type,
1033 		typename iterator_traits<_ForwardIterator>::value_type>)
1034       __glibcxx_requires_valid_range(__first, __last);
1035 
1036       return std::__unique(__first, __last,
1037 			   __gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
1038     }
1039 
1040   /**
1041    *  This is an uglified
1042    *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
1043    *              _BinaryPredicate)
1044    *  overloaded for forward iterators and output iterator as result.
1045   */
1046   template<typename _ForwardIterator, typename _OutputIterator,
1047 	   typename _BinaryPredicate>
1048     _OutputIterator
1049     __unique_copy(_ForwardIterator __first, _ForwardIterator __last,
1050 		  _OutputIterator __result, _BinaryPredicate __binary_pred,
1051 		  forward_iterator_tag, output_iterator_tag)
1052     {
1053       // concept requirements -- iterators already checked
1054       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
1055 	  typename iterator_traits<_ForwardIterator>::value_type,
1056 	  typename iterator_traits<_ForwardIterator>::value_type>)
1057 
1058       _ForwardIterator __next = __first;
1059       *__result = *__first;
1060       while (++__next != __last)
1061 	if (!__binary_pred(__first, __next))
1062 	  {
1063 	    __first = __next;
1064 	    *++__result = *__first;
1065 	  }
1066       return ++__result;
1067     }
1068 
1069   /**
1070    *  This is an uglified
1071    *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
1072    *              _BinaryPredicate)
1073    *  overloaded for input iterators and output iterator as result.
1074   */
1075   template<typename _InputIterator, typename _OutputIterator,
1076 	   typename _BinaryPredicate>
1077     _OutputIterator
1078     __unique_copy(_InputIterator __first, _InputIterator __last,
1079 		  _OutputIterator __result, _BinaryPredicate __binary_pred,
1080 		  input_iterator_tag, output_iterator_tag)
1081     {
1082       // concept requirements -- iterators already checked
1083       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
1084 	  typename iterator_traits<_InputIterator>::value_type,
1085 	  typename iterator_traits<_InputIterator>::value_type>)
1086 
1087       typename iterator_traits<_InputIterator>::value_type __value = *__first;
1088       __decltype(__gnu_cxx::__ops::__iter_comp_val(__binary_pred))
1089 	__rebound_pred
1090 	= __gnu_cxx::__ops::__iter_comp_val(__binary_pred);
1091       *__result = __value;
1092       while (++__first != __last)
1093 	if (!__rebound_pred(__first, __value))
1094 	  {
1095 	    __value = *__first;
1096 	    *++__result = __value;
1097 	  }
1098       return ++__result;
1099     }
1100 
1101   /**
1102    *  This is an uglified
1103    *  unique_copy(_InputIterator, _InputIterator, _OutputIterator,
1104    *              _BinaryPredicate)
1105    *  overloaded for input iterators and forward iterator as result.
1106   */
1107   template<typename _InputIterator, typename _ForwardIterator,
1108 	   typename _BinaryPredicate>
1109     _ForwardIterator
1110     __unique_copy(_InputIterator __first, _InputIterator __last,
1111 		  _ForwardIterator __result, _BinaryPredicate __binary_pred,
1112 		  input_iterator_tag, forward_iterator_tag)
1113     {
1114       // concept requirements -- iterators already checked
1115       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
1116 	  typename iterator_traits<_ForwardIterator>::value_type,
1117 	  typename iterator_traits<_InputIterator>::value_type>)
1118       *__result = *__first;
1119       while (++__first != __last)
1120 	if (!__binary_pred(__result, __first))
1121 	  *++__result = *__first;
1122       return ++__result;
1123     }
1124 
1125   /**
1126    *  This is an uglified reverse(_BidirectionalIterator,
1127    *                              _BidirectionalIterator)
1128    *  overloaded for bidirectional iterators.
1129   */
1130   template<typename _BidirectionalIterator>
1131     void
1132     __reverse(_BidirectionalIterator __first, _BidirectionalIterator __last,
1133 	      bidirectional_iterator_tag)
1134     {
1135       while (true)
1136 	if (__first == __last || __first == --__last)
1137 	  return;
1138 	else
1139 	  {
1140 	    std::iter_swap(__first, __last);
1141 	    ++__first;
1142 	  }
1143     }
1144 
1145   /**
1146    *  This is an uglified reverse(_BidirectionalIterator,
1147    *                              _BidirectionalIterator)
1148    *  overloaded for random access iterators.
1149   */
1150   template<typename _RandomAccessIterator>
1151     void
1152     __reverse(_RandomAccessIterator __first, _RandomAccessIterator __last,
1153 	      random_access_iterator_tag)
1154     {
1155       if (__first == __last)
1156 	return;
1157       --__last;
1158       while (__first < __last)
1159 	{
1160 	  std::iter_swap(__first, __last);
1161 	  ++__first;
1162 	  --__last;
1163 	}
1164     }
1165 
1166   /**
1167    *  @brief Reverse a sequence.
1168    *  @ingroup mutating_algorithms
1169    *  @param  __first  A bidirectional iterator.
1170    *  @param  __last   A bidirectional iterator.
1171    *  @return   reverse() returns no value.
1172    *
1173    *  Reverses the order of the elements in the range @p [__first,__last),
1174    *  so that the first element becomes the last etc.
1175    *  For every @c i such that @p 0<=i<=(__last-__first)/2), @p reverse()
1176    *  swaps @p *(__first+i) and @p *(__last-(i+1))
1177   */
1178   template<typename _BidirectionalIterator>
1179     inline void
1180     reverse(_BidirectionalIterator __first, _BidirectionalIterator __last)
1181     {
1182       // concept requirements
1183       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
1184 				  _BidirectionalIterator>)
1185       __glibcxx_requires_valid_range(__first, __last);
1186       std::__reverse(__first, __last, std::__iterator_category(__first));
1187     }
1188 
1189   /**
1190    *  @brief Copy a sequence, reversing its elements.
1191    *  @ingroup mutating_algorithms
1192    *  @param  __first   A bidirectional iterator.
1193    *  @param  __last    A bidirectional iterator.
1194    *  @param  __result  An output iterator.
1195    *  @return  An iterator designating the end of the resulting sequence.
1196    *
1197    *  Copies the elements in the range @p [__first,__last) to the
1198    *  range @p [__result,__result+(__last-__first)) such that the
1199    *  order of the elements is reversed.  For every @c i such that @p
1200    *  0<=i<=(__last-__first), @p reverse_copy() performs the
1201    *  assignment @p *(__result+(__last-__first)-1-i) = *(__first+i).
1202    *  The ranges @p [__first,__last) and @p
1203    *  [__result,__result+(__last-__first)) must not overlap.
1204   */
1205   template<typename _BidirectionalIterator, typename _OutputIterator>
1206     _OutputIterator
1207     reverse_copy(_BidirectionalIterator __first, _BidirectionalIterator __last,
1208 		 _OutputIterator __result)
1209     {
1210       // concept requirements
1211       __glibcxx_function_requires(_BidirectionalIteratorConcept<
1212 				  _BidirectionalIterator>)
1213       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
1214 		typename iterator_traits<_BidirectionalIterator>::value_type>)
1215       __glibcxx_requires_valid_range(__first, __last);
1216 
1217       while (__first != __last)
1218 	{
1219 	  --__last;
1220 	  *__result = *__last;
1221 	  ++__result;
1222 	}
1223       return __result;
1224     }
1225 
1226   /**
1227    *  This is a helper function for the rotate algorithm specialized on RAIs.
1228    *  It returns the greatest common divisor of two integer values.
1229   */
1230   template<typename _EuclideanRingElement>
1231     _EuclideanRingElement
1232     __gcd(_EuclideanRingElement __m, _EuclideanRingElement __n)
1233     {
1234       while (__n != 0)
1235 	{
1236 	  _EuclideanRingElement __t = __m % __n;
1237 	  __m = __n;
1238 	  __n = __t;
1239 	}
1240       return __m;
1241     }
1242 
1243   inline namespace _V2
1244   {
1245 
1246   /// This is a helper function for the rotate algorithm.
1247   template<typename _ForwardIterator>
1248     _ForwardIterator
1249     __rotate(_ForwardIterator __first,
1250 	     _ForwardIterator __middle,
1251 	     _ForwardIterator __last,
1252 	     forward_iterator_tag)
1253     {
1254       if (__first == __middle)
1255 	return __last;
1256       else if (__last  == __middle)
1257 	return __first;
1258 
1259       _ForwardIterator __first2 = __middle;
1260       do
1261 	{
1262 	  std::iter_swap(__first, __first2);
1263 	  ++__first;
1264 	  ++__first2;
1265 	  if (__first == __middle)
1266 	    __middle = __first2;
1267 	}
1268       while (__first2 != __last);
1269 
1270       _ForwardIterator __ret = __first;
1271 
1272       __first2 = __middle;
1273 
1274       while (__first2 != __last)
1275 	{
1276 	  std::iter_swap(__first, __first2);
1277 	  ++__first;
1278 	  ++__first2;
1279 	  if (__first == __middle)
1280 	    __middle = __first2;
1281 	  else if (__first2 == __last)
1282 	    __first2 = __middle;
1283 	}
1284       return __ret;
1285     }
1286 
1287    /// This is a helper function for the rotate algorithm.
1288   template<typename _BidirectionalIterator>
1289     _BidirectionalIterator
1290     __rotate(_BidirectionalIterator __first,
1291 	     _BidirectionalIterator __middle,
1292 	     _BidirectionalIterator __last,
1293 	      bidirectional_iterator_tag)
1294     {
1295       // concept requirements
1296       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
1297 				  _BidirectionalIterator>)
1298 
1299       if (__first == __middle)
1300 	return __last;
1301       else if (__last  == __middle)
1302 	return __first;
1303 
1304       std::__reverse(__first,  __middle, bidirectional_iterator_tag());
1305       std::__reverse(__middle, __last,   bidirectional_iterator_tag());
1306 
1307       while (__first != __middle && __middle != __last)
1308 	{
1309 	  std::iter_swap(__first, --__last);
1310 	  ++__first;
1311 	}
1312 
1313       if (__first == __middle)
1314 	{
1315 	  std::__reverse(__middle, __last,   bidirectional_iterator_tag());
1316 	  return __last;
1317 	}
1318       else
1319 	{
1320 	  std::__reverse(__first,  __middle, bidirectional_iterator_tag());
1321 	  return __first;
1322 	}
1323     }
1324 
1325   /// This is a helper function for the rotate algorithm.
1326   template<typename _RandomAccessIterator>
1327     _RandomAccessIterator
1328     __rotate(_RandomAccessIterator __first,
1329 	     _RandomAccessIterator __middle,
1330 	     _RandomAccessIterator __last,
1331 	     random_access_iterator_tag)
1332     {
1333       // concept requirements
1334       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
1335 				  _RandomAccessIterator>)
1336 
1337       if (__first == __middle)
1338 	return __last;
1339       else if (__last  == __middle)
1340 	return __first;
1341 
1342       typedef typename iterator_traits<_RandomAccessIterator>::difference_type
1343 	_Distance;
1344       typedef typename iterator_traits<_RandomAccessIterator>::value_type
1345 	_ValueType;
1346 
1347       _Distance __n = __last   - __first;
1348       _Distance __k = __middle - __first;
1349 
1350       if (__k == __n - __k)
1351 	{
1352 	  std::swap_ranges(__first, __middle, __middle);
1353 	  return __middle;
1354 	}
1355 
1356       _RandomAccessIterator __p = __first;
1357       _RandomAccessIterator __ret = __first + (__last - __middle);
1358 
1359       for (;;)
1360 	{
1361 	  if (__k < __n - __k)
1362 	    {
1363 	      if (__is_pod(_ValueType) && __k == 1)
1364 		{
1365 		  _ValueType __t = _GLIBCXX_MOVE(*__p);
1366 		  _GLIBCXX_MOVE3(__p + 1, __p + __n, __p);
1367 		  *(__p + __n - 1) = _GLIBCXX_MOVE(__t);
1368 		  return __ret;
1369 		}
1370 	      _RandomAccessIterator __q = __p + __k;
1371 	      for (_Distance __i = 0; __i < __n - __k; ++ __i)
1372 		{
1373 		  std::iter_swap(__p, __q);
1374 		  ++__p;
1375 		  ++__q;
1376 		}
1377 	      __n %= __k;
1378 	      if (__n == 0)
1379 		return __ret;
1380 	      std::swap(__n, __k);
1381 	      __k = __n - __k;
1382 	    }
1383 	  else
1384 	    {
1385 	      __k = __n - __k;
1386 	      if (__is_pod(_ValueType) && __k == 1)
1387 		{
1388 		  _ValueType __t = _GLIBCXX_MOVE(*(__p + __n - 1));
1389 		  _GLIBCXX_MOVE_BACKWARD3(__p, __p + __n - 1, __p + __n);
1390 		  *__p = _GLIBCXX_MOVE(__t);
1391 		  return __ret;
1392 		}
1393 	      _RandomAccessIterator __q = __p + __n;
1394 	      __p = __q - __k;
1395 	      for (_Distance __i = 0; __i < __n - __k; ++ __i)
1396 		{
1397 		  --__p;
1398 		  --__q;
1399 		  std::iter_swap(__p, __q);
1400 		}
1401 	      __n %= __k;
1402 	      if (__n == 0)
1403 		return __ret;
1404 	      std::swap(__n, __k);
1405 	    }
1406 	}
1407     }
1408 
1409    // _GLIBCXX_RESOLVE_LIB_DEFECTS
1410    // DR 488. rotate throws away useful information
1411   /**
1412    *  @brief Rotate the elements of a sequence.
1413    *  @ingroup mutating_algorithms
1414    *  @param  __first   A forward iterator.
1415    *  @param  __middle  A forward iterator.
1416    *  @param  __last    A forward iterator.
1417    *  @return  first + (last - middle).
1418    *
1419    *  Rotates the elements of the range @p [__first,__last) by
1420    *  @p (__middle - __first) positions so that the element at @p __middle
1421    *  is moved to @p __first, the element at @p __middle+1 is moved to
1422    *  @p __first+1 and so on for each element in the range
1423    *  @p [__first,__last).
1424    *
1425    *  This effectively swaps the ranges @p [__first,__middle) and
1426    *  @p [__middle,__last).
1427    *
1428    *  Performs
1429    *   @p *(__first+(n+(__last-__middle))%(__last-__first))=*(__first+n)
1430    *  for each @p n in the range @p [0,__last-__first).
1431   */
1432   template<typename _ForwardIterator>
1433     inline _ForwardIterator
1434     rotate(_ForwardIterator __first, _ForwardIterator __middle,
1435 	   _ForwardIterator __last)
1436     {
1437       // concept requirements
1438       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
1439 				  _ForwardIterator>)
1440       __glibcxx_requires_valid_range(__first, __middle);
1441       __glibcxx_requires_valid_range(__middle, __last);
1442 
1443       return std::__rotate(__first, __middle, __last,
1444 			   std::__iterator_category(__first));
1445     }
1446 
1447   } // namespace _V2
1448 
1449   /**
1450    *  @brief Copy a sequence, rotating its elements.
1451    *  @ingroup mutating_algorithms
1452    *  @param  __first   A forward iterator.
1453    *  @param  __middle  A forward iterator.
1454    *  @param  __last    A forward iterator.
1455    *  @param  __result  An output iterator.
1456    *  @return   An iterator designating the end of the resulting sequence.
1457    *
1458    *  Copies the elements of the range @p [__first,__last) to the
1459    *  range beginning at @result, rotating the copied elements by
1460    *  @p (__middle-__first) positions so that the element at @p __middle
1461    *  is moved to @p __result, the element at @p __middle+1 is moved
1462    *  to @p __result+1 and so on for each element in the range @p
1463    *  [__first,__last).
1464    *
1465    *  Performs
1466    *  @p *(__result+(n+(__last-__middle))%(__last-__first))=*(__first+n)
1467    *  for each @p n in the range @p [0,__last-__first).
1468   */
1469   template<typename _ForwardIterator, typename _OutputIterator>
1470     inline _OutputIterator
1471     rotate_copy(_ForwardIterator __first, _ForwardIterator __middle,
1472 		_ForwardIterator __last, _OutputIterator __result)
1473     {
1474       // concept requirements
1475       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
1476       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
1477 		typename iterator_traits<_ForwardIterator>::value_type>)
1478       __glibcxx_requires_valid_range(__first, __middle);
1479       __glibcxx_requires_valid_range(__middle, __last);
1480 
1481       return std::copy(__first, __middle,
1482 		       std::copy(__middle, __last, __result));
1483     }
1484 
1485   /// This is a helper function...
1486   template<typename _ForwardIterator, typename _Predicate>
1487     _ForwardIterator
1488     __partition(_ForwardIterator __first, _ForwardIterator __last,
1489 		_Predicate __pred, forward_iterator_tag)
1490     {
1491       if (__first == __last)
1492 	return __first;
1493 
1494       while (__pred(*__first))
1495 	if (++__first == __last)
1496 	  return __first;
1497 
1498       _ForwardIterator __next = __first;
1499 
1500       while (++__next != __last)
1501 	if (__pred(*__next))
1502 	  {
1503 	    std::iter_swap(__first, __next);
1504 	    ++__first;
1505 	  }
1506 
1507       return __first;
1508     }
1509 
1510   /// This is a helper function...
1511   template<typename _BidirectionalIterator, typename _Predicate>
1512     _BidirectionalIterator
1513     __partition(_BidirectionalIterator __first, _BidirectionalIterator __last,
1514 		_Predicate __pred, bidirectional_iterator_tag)
1515     {
1516       while (true)
1517 	{
1518 	  while (true)
1519 	    if (__first == __last)
1520 	      return __first;
1521 	    else if (__pred(*__first))
1522 	      ++__first;
1523 	    else
1524 	      break;
1525 	  --__last;
1526 	  while (true)
1527 	    if (__first == __last)
1528 	      return __first;
1529 	    else if (!bool(__pred(*__last)))
1530 	      --__last;
1531 	    else
1532 	      break;
1533 	  std::iter_swap(__first, __last);
1534 	  ++__first;
1535 	}
1536     }
1537 
1538   // partition
1539 
1540   /// This is a helper function...
1541   /// Requires __first != __last and !__pred(__first)
1542   /// and __len == distance(__first, __last).
1543   ///
1544   /// !__pred(__first) allows us to guarantee that we don't
1545   /// move-assign an element onto itself.
1546   template<typename _ForwardIterator, typename _Pointer, typename _Predicate,
1547 	   typename _Distance>
1548     _ForwardIterator
1549     __stable_partition_adaptive(_ForwardIterator __first,
1550 				_ForwardIterator __last,
1551 				_Predicate __pred, _Distance __len,
1552 				_Pointer __buffer,
1553 				_Distance __buffer_size)
1554     {
1555       if (__len == 1)
1556 	return __first;
1557 
1558       if (__len <= __buffer_size)
1559 	{
1560 	  _ForwardIterator __result1 = __first;
1561 	  _Pointer __result2 = __buffer;
1562 
1563 	  // The precondition guarantees that !__pred(__first), so
1564 	  // move that element to the buffer before starting the loop.
1565 	  // This ensures that we only call __pred once per element.
1566 	  *__result2 = _GLIBCXX_MOVE(*__first);
1567 	  ++__result2;
1568 	  ++__first;
1569 	  for (; __first != __last; ++__first)
1570 	    if (__pred(__first))
1571 	      {
1572 		*__result1 = _GLIBCXX_MOVE(*__first);
1573 		++__result1;
1574 	      }
1575 	    else
1576 	      {
1577 		*__result2 = _GLIBCXX_MOVE(*__first);
1578 		++__result2;
1579 	      }
1580 
1581 	  _GLIBCXX_MOVE3(__buffer, __result2, __result1);
1582 	  return __result1;
1583 	}
1584 
1585       _ForwardIterator __middle = __first;
1586       std::advance(__middle, __len / 2);
1587       _ForwardIterator __left_split =
1588 	std::__stable_partition_adaptive(__first, __middle, __pred,
1589 					 __len / 2, __buffer,
1590 					 __buffer_size);
1591 
1592       // Advance past true-predicate values to satisfy this
1593       // function's preconditions.
1594       _Distance __right_len = __len - __len / 2;
1595       _ForwardIterator __right_split =
1596 	std::__find_if_not_n(__middle, __right_len, __pred);
1597 
1598       if (__right_len)
1599 	__right_split =
1600 	  std::__stable_partition_adaptive(__right_split, __last, __pred,
1601 					   __right_len,
1602 					   __buffer, __buffer_size);
1603 
1604       std::rotate(__left_split, __middle, __right_split);
1605       std::advance(__left_split, std::distance(__middle, __right_split));
1606       return __left_split;
1607     }
1608 
1609   template<typename _ForwardIterator, typename _Predicate>
1610     _ForwardIterator
1611     __stable_partition(_ForwardIterator __first, _ForwardIterator __last,
1612 		       _Predicate __pred)
1613     {
1614       __first = std::__find_if_not(__first, __last, __pred);
1615 
1616       if (__first == __last)
1617 	return __first;
1618 
1619       typedef typename iterator_traits<_ForwardIterator>::value_type
1620 	_ValueType;
1621       typedef typename iterator_traits<_ForwardIterator>::difference_type
1622 	_DistanceType;
1623 
1624       _Temporary_buffer<_ForwardIterator, _ValueType> __buf(__first, __last);
1625       return
1626 	std::__stable_partition_adaptive(__first, __last, __pred,
1627 					 _DistanceType(__buf.requested_size()),
1628 					 __buf.begin(),
1629 					 _DistanceType(__buf.size()));
1630     }
1631 
1632   /**
1633    *  @brief Move elements for which a predicate is true to the beginning
1634    *         of a sequence, preserving relative ordering.
1635    *  @ingroup mutating_algorithms
1636    *  @param  __first   A forward iterator.
1637    *  @param  __last    A forward iterator.
1638    *  @param  __pred    A predicate functor.
1639    *  @return  An iterator @p middle such that @p __pred(i) is true for each
1640    *  iterator @p i in the range @p [first,middle) and false for each @p i
1641    *  in the range @p [middle,last).
1642    *
1643    *  Performs the same function as @p partition() with the additional
1644    *  guarantee that the relative ordering of elements in each group is
1645    *  preserved, so any two elements @p x and @p y in the range
1646    *  @p [__first,__last) such that @p __pred(x)==__pred(y) will have the same
1647    *  relative ordering after calling @p stable_partition().
1648   */
1649   template<typename _ForwardIterator, typename _Predicate>
1650     inline _ForwardIterator
1651     stable_partition(_ForwardIterator __first, _ForwardIterator __last,
1652 		     _Predicate __pred)
1653     {
1654       // concept requirements
1655       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
1656 				  _ForwardIterator>)
1657       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
1658 	    typename iterator_traits<_ForwardIterator>::value_type>)
1659       __glibcxx_requires_valid_range(__first, __last);
1660 
1661       return std::__stable_partition(__first, __last,
1662 				     __gnu_cxx::__ops::__pred_iter(__pred));
1663     }
1664 
1665   /// This is a helper function for the sort routines.
1666   template<typename _RandomAccessIterator, typename _Compare>
1667     void
1668     __heap_select(_RandomAccessIterator __first,
1669 		  _RandomAccessIterator __middle,
1670 		  _RandomAccessIterator __last, _Compare __comp)
1671     {
1672       std::__make_heap(__first, __middle, __comp);
1673       for (_RandomAccessIterator __i = __middle; __i < __last; ++__i)
1674 	if (__comp(__i, __first))
1675 	  std::__pop_heap(__first, __middle, __i, __comp);
1676     }
1677 
1678   // partial_sort
1679 
1680   template<typename _InputIterator, typename _RandomAccessIterator,
1681 	   typename _Compare>
1682     _RandomAccessIterator
1683     __partial_sort_copy(_InputIterator __first, _InputIterator __last,
1684 			_RandomAccessIterator __result_first,
1685 			_RandomAccessIterator __result_last,
1686 			_Compare __comp)
1687     {
1688       typedef typename iterator_traits<_InputIterator>::value_type
1689 	_InputValueType;
1690       typedef iterator_traits<_RandomAccessIterator> _RItTraits;
1691       typedef typename _RItTraits::difference_type _DistanceType;
1692 
1693       if (__result_first == __result_last)
1694 	return __result_last;
1695       _RandomAccessIterator __result_real_last = __result_first;
1696       while (__first != __last && __result_real_last != __result_last)
1697 	{
1698 	  *__result_real_last = *__first;
1699 	  ++__result_real_last;
1700 	  ++__first;
1701 	}
1702 
1703       std::__make_heap(__result_first, __result_real_last, __comp);
1704       while (__first != __last)
1705 	{
1706 	  if (__comp(__first, __result_first))
1707 	    std::__adjust_heap(__result_first, _DistanceType(0),
1708 			       _DistanceType(__result_real_last
1709 					     - __result_first),
1710 			       _InputValueType(*__first), __comp);
1711 	  ++__first;
1712 	}
1713       std::__sort_heap(__result_first, __result_real_last, __comp);
1714       return __result_real_last;
1715     }
1716 
1717   /**
1718    *  @brief Copy the smallest elements of a sequence.
1719    *  @ingroup sorting_algorithms
1720    *  @param  __first   An iterator.
1721    *  @param  __last    Another iterator.
1722    *  @param  __result_first   A random-access iterator.
1723    *  @param  __result_last    Another random-access iterator.
1724    *  @return   An iterator indicating the end of the resulting sequence.
1725    *
1726    *  Copies and sorts the smallest N values from the range @p [__first,__last)
1727    *  to the range beginning at @p __result_first, where the number of
1728    *  elements to be copied, @p N, is the smaller of @p (__last-__first) and
1729    *  @p (__result_last-__result_first).
1730    *  After the sort if @e i and @e j are iterators in the range
1731    *  @p [__result_first,__result_first+N) such that i precedes j then
1732    *  *j<*i is false.
1733    *  The value returned is @p __result_first+N.
1734   */
1735   template<typename _InputIterator, typename _RandomAccessIterator>
1736     inline _RandomAccessIterator
1737     partial_sort_copy(_InputIterator __first, _InputIterator __last,
1738 		      _RandomAccessIterator __result_first,
1739 		      _RandomAccessIterator __result_last)
1740     {
1741 #ifdef _GLIBCXX_CONCEPT_CHECKS
1742       typedef typename iterator_traits<_InputIterator>::value_type
1743 	_InputValueType;
1744       typedef typename iterator_traits<_RandomAccessIterator>::value_type
1745 	_OutputValueType;
1746 #endif
1747 
1748       // concept requirements
1749       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
1750       __glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
1751 				  _OutputValueType>)
1752       __glibcxx_function_requires(_LessThanOpConcept<_InputValueType,
1753 						     _OutputValueType>)
1754       __glibcxx_function_requires(_LessThanComparableConcept<_OutputValueType>)
1755       __glibcxx_requires_valid_range(__first, __last);
1756       __glibcxx_requires_irreflexive(__first, __last);
1757       __glibcxx_requires_valid_range(__result_first, __result_last);
1758 
1759       return std::__partial_sort_copy(__first, __last,
1760 				      __result_first, __result_last,
1761 				      __gnu_cxx::__ops::__iter_less_iter());
1762     }
1763 
1764   /**
1765    *  @brief Copy the smallest elements of a sequence using a predicate for
1766    *         comparison.
1767    *  @ingroup sorting_algorithms
1768    *  @param  __first   An input iterator.
1769    *  @param  __last    Another input iterator.
1770    *  @param  __result_first   A random-access iterator.
1771    *  @param  __result_last    Another random-access iterator.
1772    *  @param  __comp    A comparison functor.
1773    *  @return   An iterator indicating the end of the resulting sequence.
1774    *
1775    *  Copies and sorts the smallest N values from the range @p [__first,__last)
1776    *  to the range beginning at @p result_first, where the number of
1777    *  elements to be copied, @p N, is the smaller of @p (__last-__first) and
1778    *  @p (__result_last-__result_first).
1779    *  After the sort if @e i and @e j are iterators in the range
1780    *  @p [__result_first,__result_first+N) such that i precedes j then
1781    *  @p __comp(*j,*i) is false.
1782    *  The value returned is @p __result_first+N.
1783   */
1784   template<typename _InputIterator, typename _RandomAccessIterator,
1785 	   typename _Compare>
1786     inline _RandomAccessIterator
1787     partial_sort_copy(_InputIterator __first, _InputIterator __last,
1788 		      _RandomAccessIterator __result_first,
1789 		      _RandomAccessIterator __result_last,
1790 		      _Compare __comp)
1791     {
1792 #ifdef _GLIBCXX_CONCEPT_CHECKS
1793       typedef typename iterator_traits<_InputIterator>::value_type
1794 	_InputValueType;
1795       typedef typename iterator_traits<_RandomAccessIterator>::value_type
1796 	_OutputValueType;
1797 #endif
1798 
1799       // concept requirements
1800       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
1801       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
1802 				  _RandomAccessIterator>)
1803       __glibcxx_function_requires(_ConvertibleConcept<_InputValueType,
1804 				  _OutputValueType>)
1805       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
1806 				  _InputValueType, _OutputValueType>)
1807       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
1808 				  _OutputValueType, _OutputValueType>)
1809       __glibcxx_requires_valid_range(__first, __last);
1810       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
1811       __glibcxx_requires_valid_range(__result_first, __result_last);
1812 
1813       return std::__partial_sort_copy(__first, __last,
1814 				      __result_first, __result_last,
1815 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
1816     }
1817 
1818   /// This is a helper function for the sort routine.
1819   template<typename _RandomAccessIterator, typename _Compare>
1820     void
1821     __unguarded_linear_insert(_RandomAccessIterator __last,
1822 			      _Compare __comp)
1823     {
1824       typename iterator_traits<_RandomAccessIterator>::value_type
1825 	__val = _GLIBCXX_MOVE(*__last);
1826       _RandomAccessIterator __next = __last;
1827       --__next;
1828       while (__comp(__val, __next))
1829 	{
1830 	  *__last = _GLIBCXX_MOVE(*__next);
1831 	  __last = __next;
1832 	  --__next;
1833 	}
1834       *__last = _GLIBCXX_MOVE(__val);
1835     }
1836 
1837   /// This is a helper function for the sort routine.
1838   template<typename _RandomAccessIterator, typename _Compare>
1839     void
1840     __insertion_sort(_RandomAccessIterator __first,
1841 		     _RandomAccessIterator __last, _Compare __comp)
1842     {
1843       if (__first == __last) return;
1844 
1845       for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
1846 	{
1847 	  if (__comp(__i, __first))
1848 	    {
1849 	      typename iterator_traits<_RandomAccessIterator>::value_type
1850 		__val = _GLIBCXX_MOVE(*__i);
1851 	      _GLIBCXX_MOVE_BACKWARD3(__first, __i, __i + 1);
1852 	      *__first = _GLIBCXX_MOVE(__val);
1853 	    }
1854 	  else
1855 	    std::__unguarded_linear_insert(__i,
1856 				__gnu_cxx::__ops::__val_comp_iter(__comp));
1857 	}
1858     }
1859 
1860   /// This is a helper function for the sort routine.
1861   template<typename _RandomAccessIterator, typename _Compare>
1862     inline void
1863     __unguarded_insertion_sort(_RandomAccessIterator __first,
1864 			       _RandomAccessIterator __last, _Compare __comp)
1865     {
1866       for (_RandomAccessIterator __i = __first; __i != __last; ++__i)
1867 	std::__unguarded_linear_insert(__i,
1868 				__gnu_cxx::__ops::__val_comp_iter(__comp));
1869     }
1870 
1871   /**
1872    *  @doctodo
1873    *  This controls some aspect of the sort routines.
1874   */
1875   enum { _S_threshold = 16 };
1876 
1877   /// This is a helper function for the sort routine.
1878   template<typename _RandomAccessIterator, typename _Compare>
1879     void
1880     __final_insertion_sort(_RandomAccessIterator __first,
1881 			   _RandomAccessIterator __last, _Compare __comp)
1882     {
1883       if (__last - __first > int(_S_threshold))
1884 	{
1885 	  std::__insertion_sort(__first, __first + int(_S_threshold), __comp);
1886 	  std::__unguarded_insertion_sort(__first + int(_S_threshold), __last,
1887 					  __comp);
1888 	}
1889       else
1890 	std::__insertion_sort(__first, __last, __comp);
1891     }
1892 
1893   /// This is a helper function...
1894   template<typename _RandomAccessIterator, typename _Compare>
1895     _RandomAccessIterator
1896     __unguarded_partition(_RandomAccessIterator __first,
1897 			  _RandomAccessIterator __last,
1898 			  _RandomAccessIterator __pivot, _Compare __comp)
1899     {
1900       while (true)
1901 	{
1902 	  while (__comp(__first, __pivot))
1903 	    ++__first;
1904 	  --__last;
1905 	  while (__comp(__pivot, __last))
1906 	    --__last;
1907 	  if (!(__first < __last))
1908 	    return __first;
1909 	  std::iter_swap(__first, __last);
1910 	  ++__first;
1911 	}
1912     }
1913 
1914   /// This is a helper function...
1915   template<typename _RandomAccessIterator, typename _Compare>
1916     inline _RandomAccessIterator
1917     __unguarded_partition_pivot(_RandomAccessIterator __first,
1918 				_RandomAccessIterator __last, _Compare __comp)
1919     {
1920       _RandomAccessIterator __mid = __first + (__last - __first) / 2;
1921       std::__move_median_to_first(__first, __first + 1, __mid, __last - 1,
1922 				  __comp);
1923       return std::__unguarded_partition(__first + 1, __last, __first, __comp);
1924     }
1925 
1926   template<typename _RandomAccessIterator, typename _Compare>
1927     inline void
1928     __partial_sort(_RandomAccessIterator __first,
1929 		   _RandomAccessIterator __middle,
1930 		   _RandomAccessIterator __last,
1931 		   _Compare __comp)
1932     {
1933       std::__heap_select(__first, __middle, __last, __comp);
1934       std::__sort_heap(__first, __middle, __comp);
1935     }
1936 
1937   /// This is a helper function for the sort routine.
1938   template<typename _RandomAccessIterator, typename _Size, typename _Compare>
1939     void
1940     __introsort_loop(_RandomAccessIterator __first,
1941 		     _RandomAccessIterator __last,
1942 		     _Size __depth_limit, _Compare __comp)
1943     {
1944       while (__last - __first > int(_S_threshold))
1945 	{
1946 	  if (__depth_limit == 0)
1947 	    {
1948 	      std::__partial_sort(__first, __last, __last, __comp);
1949 	      return;
1950 	    }
1951 	  --__depth_limit;
1952 	  _RandomAccessIterator __cut =
1953 	    std::__unguarded_partition_pivot(__first, __last, __comp);
1954 	  std::__introsort_loop(__cut, __last, __depth_limit, __comp);
1955 	  __last = __cut;
1956 	}
1957     }
1958 
1959   // sort
1960 
1961   template<typename _RandomAccessIterator, typename _Compare>
1962     inline void
1963     __sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
1964 	   _Compare __comp)
1965     {
1966       if (__first != __last)
1967 	{
1968 	  std::__introsort_loop(__first, __last,
1969 				std::__lg(__last - __first) * 2,
1970 				__comp);
1971 	  std::__final_insertion_sort(__first, __last, __comp);
1972 	}
1973     }
1974 
1975   template<typename _RandomAccessIterator, typename _Size, typename _Compare>
1976     void
1977     __introselect(_RandomAccessIterator __first, _RandomAccessIterator __nth,
1978 		  _RandomAccessIterator __last, _Size __depth_limit,
1979 		  _Compare __comp)
1980     {
1981       while (__last - __first > 3)
1982 	{
1983 	  if (__depth_limit == 0)
1984 	    {
1985 	      std::__heap_select(__first, __nth + 1, __last, __comp);
1986 	      // Place the nth largest element in its final position.
1987 	      std::iter_swap(__first, __nth);
1988 	      return;
1989 	    }
1990 	  --__depth_limit;
1991 	  _RandomAccessIterator __cut =
1992 	    std::__unguarded_partition_pivot(__first, __last, __comp);
1993 	  if (__cut <= __nth)
1994 	    __first = __cut;
1995 	  else
1996 	    __last = __cut;
1997 	}
1998       std::__insertion_sort(__first, __last, __comp);
1999     }
2000 
2001   // nth_element
2002 
2003   // lower_bound moved to stl_algobase.h
2004 
2005   /**
2006    *  @brief Finds the first position in which @p __val could be inserted
2007    *         without changing the ordering.
2008    *  @ingroup binary_search_algorithms
2009    *  @param  __first   An iterator.
2010    *  @param  __last    Another iterator.
2011    *  @param  __val     The search term.
2012    *  @param  __comp    A functor to use for comparisons.
2013    *  @return An iterator pointing to the first element <em>not less
2014    *           than</em> @p __val, or end() if every element is less
2015    *           than @p __val.
2016    *  @ingroup binary_search_algorithms
2017    *
2018    *  The comparison function should have the same effects on ordering as
2019    *  the function used for the initial sort.
2020   */
2021   template<typename _ForwardIterator, typename _Tp, typename _Compare>
2022     inline _ForwardIterator
2023     lower_bound(_ForwardIterator __first, _ForwardIterator __last,
2024 		const _Tp& __val, _Compare __comp)
2025     {
2026       // concept requirements
2027       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2028       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2029 	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
2030       __glibcxx_requires_partitioned_lower_pred(__first, __last,
2031 						__val, __comp);
2032 
2033       return std::__lower_bound(__first, __last, __val,
2034 				__gnu_cxx::__ops::__iter_comp_val(__comp));
2035     }
2036 
2037   template<typename _ForwardIterator, typename _Tp, typename _Compare>
2038     _ForwardIterator
2039     __upper_bound(_ForwardIterator __first, _ForwardIterator __last,
2040 		  const _Tp& __val, _Compare __comp)
2041     {
2042       typedef typename iterator_traits<_ForwardIterator>::difference_type
2043 	_DistanceType;
2044 
2045       _DistanceType __len = std::distance(__first, __last);
2046 
2047       while (__len > 0)
2048 	{
2049 	  _DistanceType __half = __len >> 1;
2050 	  _ForwardIterator __middle = __first;
2051 	  std::advance(__middle, __half);
2052 	  if (__comp(__val, __middle))
2053 	    __len = __half;
2054 	  else
2055 	    {
2056 	      __first = __middle;
2057 	      ++__first;
2058 	      __len = __len - __half - 1;
2059 	    }
2060 	}
2061       return __first;
2062     }
2063 
2064   /**
2065    *  @brief Finds the last position in which @p __val could be inserted
2066    *         without changing the ordering.
2067    *  @ingroup binary_search_algorithms
2068    *  @param  __first   An iterator.
2069    *  @param  __last    Another iterator.
2070    *  @param  __val     The search term.
2071    *  @return  An iterator pointing to the first element greater than @p __val,
2072    *           or end() if no elements are greater than @p __val.
2073    *  @ingroup binary_search_algorithms
2074   */
2075   template<typename _ForwardIterator, typename _Tp>
2076     inline _ForwardIterator
2077     upper_bound(_ForwardIterator __first, _ForwardIterator __last,
2078 		const _Tp& __val)
2079     {
2080       // concept requirements
2081       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2082       __glibcxx_function_requires(_LessThanOpConcept<
2083 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2084       __glibcxx_requires_partitioned_upper(__first, __last, __val);
2085 
2086       return std::__upper_bound(__first, __last, __val,
2087 				__gnu_cxx::__ops::__val_less_iter());
2088     }
2089 
2090   /**
2091    *  @brief Finds the last position in which @p __val could be inserted
2092    *         without changing the ordering.
2093    *  @ingroup binary_search_algorithms
2094    *  @param  __first   An iterator.
2095    *  @param  __last    Another iterator.
2096    *  @param  __val     The search term.
2097    *  @param  __comp    A functor to use for comparisons.
2098    *  @return  An iterator pointing to the first element greater than @p __val,
2099    *           or end() if no elements are greater than @p __val.
2100    *  @ingroup binary_search_algorithms
2101    *
2102    *  The comparison function should have the same effects on ordering as
2103    *  the function used for the initial sort.
2104   */
2105   template<typename _ForwardIterator, typename _Tp, typename _Compare>
2106     inline _ForwardIterator
2107     upper_bound(_ForwardIterator __first, _ForwardIterator __last,
2108 		const _Tp& __val, _Compare __comp)
2109     {
2110       // concept requirements
2111       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2112       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2113 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2114       __glibcxx_requires_partitioned_upper_pred(__first, __last,
2115 						__val, __comp);
2116 
2117       return std::__upper_bound(__first, __last, __val,
2118 				__gnu_cxx::__ops::__val_comp_iter(__comp));
2119     }
2120 
2121   template<typename _ForwardIterator, typename _Tp,
2122 	   typename _CompareItTp, typename _CompareTpIt>
2123     pair<_ForwardIterator, _ForwardIterator>
2124     __equal_range(_ForwardIterator __first, _ForwardIterator __last,
2125 		  const _Tp& __val,
2126 		  _CompareItTp __comp_it_val, _CompareTpIt __comp_val_it)
2127     {
2128       typedef typename iterator_traits<_ForwardIterator>::difference_type
2129 	_DistanceType;
2130 
2131       _DistanceType __len = std::distance(__first, __last);
2132 
2133       while (__len > 0)
2134 	{
2135 	  _DistanceType __half = __len >> 1;
2136 	  _ForwardIterator __middle = __first;
2137 	  std::advance(__middle, __half);
2138 	  if (__comp_it_val(__middle, __val))
2139 	    {
2140 	      __first = __middle;
2141 	      ++__first;
2142 	      __len = __len - __half - 1;
2143 	    }
2144 	  else if (__comp_val_it(__val, __middle))
2145 	    __len = __half;
2146 	  else
2147 	    {
2148 	      _ForwardIterator __left
2149 		= std::__lower_bound(__first, __middle, __val, __comp_it_val);
2150 	      std::advance(__first, __len);
2151 	      _ForwardIterator __right
2152 		= std::__upper_bound(++__middle, __first, __val, __comp_val_it);
2153 	      return pair<_ForwardIterator, _ForwardIterator>(__left, __right);
2154 	    }
2155 	}
2156       return pair<_ForwardIterator, _ForwardIterator>(__first, __first);
2157     }
2158 
2159   /**
2160    *  @brief Finds the largest subrange in which @p __val could be inserted
2161    *         at any place in it without changing the ordering.
2162    *  @ingroup binary_search_algorithms
2163    *  @param  __first   An iterator.
2164    *  @param  __last    Another iterator.
2165    *  @param  __val     The search term.
2166    *  @return  An pair of iterators defining the subrange.
2167    *  @ingroup binary_search_algorithms
2168    *
2169    *  This is equivalent to
2170    *  @code
2171    *    std::make_pair(lower_bound(__first, __last, __val),
2172    *                   upper_bound(__first, __last, __val))
2173    *  @endcode
2174    *  but does not actually call those functions.
2175   */
2176   template<typename _ForwardIterator, typename _Tp>
2177     inline pair<_ForwardIterator, _ForwardIterator>
2178     equal_range(_ForwardIterator __first, _ForwardIterator __last,
2179 		const _Tp& __val)
2180     {
2181       // concept requirements
2182       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2183       __glibcxx_function_requires(_LessThanOpConcept<
2184 	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
2185       __glibcxx_function_requires(_LessThanOpConcept<
2186 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2187       __glibcxx_requires_partitioned_lower(__first, __last, __val);
2188       __glibcxx_requires_partitioned_upper(__first, __last, __val);
2189 
2190       return std::__equal_range(__first, __last, __val,
2191 				__gnu_cxx::__ops::__iter_less_val(),
2192 				__gnu_cxx::__ops::__val_less_iter());
2193     }
2194 
2195   /**
2196    *  @brief Finds the largest subrange in which @p __val could be inserted
2197    *         at any place in it without changing the ordering.
2198    *  @param  __first   An iterator.
2199    *  @param  __last    Another iterator.
2200    *  @param  __val     The search term.
2201    *  @param  __comp    A functor to use for comparisons.
2202    *  @return  An pair of iterators defining the subrange.
2203    *  @ingroup binary_search_algorithms
2204    *
2205    *  This is equivalent to
2206    *  @code
2207    *    std::make_pair(lower_bound(__first, __last, __val, __comp),
2208    *                   upper_bound(__first, __last, __val, __comp))
2209    *  @endcode
2210    *  but does not actually call those functions.
2211   */
2212   template<typename _ForwardIterator, typename _Tp, typename _Compare>
2213     inline pair<_ForwardIterator, _ForwardIterator>
2214     equal_range(_ForwardIterator __first, _ForwardIterator __last,
2215 		const _Tp& __val, _Compare __comp)
2216     {
2217       // concept requirements
2218       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2219       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2220 	typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
2221       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2222 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2223       __glibcxx_requires_partitioned_lower_pred(__first, __last,
2224 						__val, __comp);
2225       __glibcxx_requires_partitioned_upper_pred(__first, __last,
2226 						__val, __comp);
2227 
2228       return std::__equal_range(__first, __last, __val,
2229 				__gnu_cxx::__ops::__iter_comp_val(__comp),
2230 				__gnu_cxx::__ops::__val_comp_iter(__comp));
2231     }
2232 
2233   /**
2234    *  @brief Determines whether an element exists in a range.
2235    *  @ingroup binary_search_algorithms
2236    *  @param  __first   An iterator.
2237    *  @param  __last    Another iterator.
2238    *  @param  __val     The search term.
2239    *  @return True if @p __val (or its equivalent) is in [@p
2240    *  __first,@p __last ].
2241    *
2242    *  Note that this does not actually return an iterator to @p __val.  For
2243    *  that, use std::find or a container's specialized find member functions.
2244   */
2245   template<typename _ForwardIterator, typename _Tp>
2246     bool
2247     binary_search(_ForwardIterator __first, _ForwardIterator __last,
2248 		  const _Tp& __val)
2249     {
2250       // concept requirements
2251       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2252       __glibcxx_function_requires(_LessThanOpConcept<
2253 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2254       __glibcxx_requires_partitioned_lower(__first, __last, __val);
2255       __glibcxx_requires_partitioned_upper(__first, __last, __val);
2256 
2257       _ForwardIterator __i
2258 	= std::__lower_bound(__first, __last, __val,
2259 			     __gnu_cxx::__ops::__iter_less_val());
2260       return __i != __last && !(__val < *__i);
2261     }
2262 
2263   /**
2264    *  @brief Determines whether an element exists in a range.
2265    *  @ingroup binary_search_algorithms
2266    *  @param  __first   An iterator.
2267    *  @param  __last    Another iterator.
2268    *  @param  __val     The search term.
2269    *  @param  __comp    A functor to use for comparisons.
2270    *  @return  True if @p __val (or its equivalent) is in @p [__first,__last].
2271    *
2272    *  Note that this does not actually return an iterator to @p __val.  For
2273    *  that, use std::find or a container's specialized find member functions.
2274    *
2275    *  The comparison function should have the same effects on ordering as
2276    *  the function used for the initial sort.
2277   */
2278   template<typename _ForwardIterator, typename _Tp, typename _Compare>
2279     bool
2280     binary_search(_ForwardIterator __first, _ForwardIterator __last,
2281 		  const _Tp& __val, _Compare __comp)
2282     {
2283       // concept requirements
2284       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
2285       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2286 	_Tp, typename iterator_traits<_ForwardIterator>::value_type>)
2287       __glibcxx_requires_partitioned_lower_pred(__first, __last,
2288 						__val, __comp);
2289       __glibcxx_requires_partitioned_upper_pred(__first, __last,
2290 						__val, __comp);
2291 
2292       _ForwardIterator __i
2293 	= std::__lower_bound(__first, __last, __val,
2294 			     __gnu_cxx::__ops::__iter_comp_val(__comp));
2295       return __i != __last && !bool(__comp(__val, *__i));
2296     }
2297 
2298   // merge
2299 
2300   /// This is a helper function for the __merge_adaptive routines.
2301   template<typename _InputIterator1, typename _InputIterator2,
2302 	   typename _OutputIterator, typename _Compare>
2303     void
2304     __move_merge_adaptive(_InputIterator1 __first1, _InputIterator1 __last1,
2305 			  _InputIterator2 __first2, _InputIterator2 __last2,
2306 			  _OutputIterator __result, _Compare __comp)
2307     {
2308       while (__first1 != __last1 && __first2 != __last2)
2309 	{
2310 	  if (__comp(__first2, __first1))
2311 	    {
2312 	      *__result = _GLIBCXX_MOVE(*__first2);
2313 	      ++__first2;
2314 	    }
2315 	  else
2316 	    {
2317 	      *__result = _GLIBCXX_MOVE(*__first1);
2318 	      ++__first1;
2319 	    }
2320 	  ++__result;
2321 	}
2322       if (__first1 != __last1)
2323 	_GLIBCXX_MOVE3(__first1, __last1, __result);
2324     }
2325 
2326   /// This is a helper function for the __merge_adaptive routines.
2327   template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
2328 	   typename _BidirectionalIterator3, typename _Compare>
2329     void
2330     __move_merge_adaptive_backward(_BidirectionalIterator1 __first1,
2331 				   _BidirectionalIterator1 __last1,
2332 				   _BidirectionalIterator2 __first2,
2333 				   _BidirectionalIterator2 __last2,
2334 				   _BidirectionalIterator3 __result,
2335 				   _Compare __comp)
2336     {
2337       if (__first1 == __last1)
2338 	{
2339 	  _GLIBCXX_MOVE_BACKWARD3(__first2, __last2, __result);
2340 	  return;
2341 	}
2342       else if (__first2 == __last2)
2343 	return;
2344 
2345       --__last1;
2346       --__last2;
2347       while (true)
2348 	{
2349 	  if (__comp(__last2, __last1))
2350 	    {
2351 	      *--__result = _GLIBCXX_MOVE(*__last1);
2352 	      if (__first1 == __last1)
2353 		{
2354 		  _GLIBCXX_MOVE_BACKWARD3(__first2, ++__last2, __result);
2355 		  return;
2356 		}
2357 	      --__last1;
2358 	    }
2359 	  else
2360 	    {
2361 	      *--__result = _GLIBCXX_MOVE(*__last2);
2362 	      if (__first2 == __last2)
2363 		return;
2364 	      --__last2;
2365 	    }
2366 	}
2367     }
2368 
2369   /// This is a helper function for the merge routines.
2370   template<typename _BidirectionalIterator1, typename _BidirectionalIterator2,
2371 	   typename _Distance>
2372     _BidirectionalIterator1
2373     __rotate_adaptive(_BidirectionalIterator1 __first,
2374 		      _BidirectionalIterator1 __middle,
2375 		      _BidirectionalIterator1 __last,
2376 		      _Distance __len1, _Distance __len2,
2377 		      _BidirectionalIterator2 __buffer,
2378 		      _Distance __buffer_size)
2379     {
2380       _BidirectionalIterator2 __buffer_end;
2381       if (__len1 > __len2 && __len2 <= __buffer_size)
2382 	{
2383 	  if (__len2)
2384 	    {
2385 	      __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
2386 	      _GLIBCXX_MOVE_BACKWARD3(__first, __middle, __last);
2387 	      return _GLIBCXX_MOVE3(__buffer, __buffer_end, __first);
2388 	    }
2389 	  else
2390 	    return __first;
2391 	}
2392       else if (__len1 <= __buffer_size)
2393 	{
2394 	  if (__len1)
2395 	    {
2396 	      __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
2397 	      _GLIBCXX_MOVE3(__middle, __last, __first);
2398 	      return _GLIBCXX_MOVE_BACKWARD3(__buffer, __buffer_end, __last);
2399 	    }
2400 	  else
2401 	    return __last;
2402 	}
2403       else
2404 	{
2405 	  std::rotate(__first, __middle, __last);
2406 	  std::advance(__first, std::distance(__middle, __last));
2407 	  return __first;
2408 	}
2409     }
2410 
2411   /// This is a helper function for the merge routines.
2412   template<typename _BidirectionalIterator, typename _Distance,
2413 	   typename _Pointer, typename _Compare>
2414     void
2415     __merge_adaptive(_BidirectionalIterator __first,
2416 		     _BidirectionalIterator __middle,
2417 		     _BidirectionalIterator __last,
2418 		     _Distance __len1, _Distance __len2,
2419 		     _Pointer __buffer, _Distance __buffer_size,
2420 		     _Compare __comp)
2421     {
2422       if (__len1 <= __len2 && __len1 <= __buffer_size)
2423 	{
2424 	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__first, __middle, __buffer);
2425 	  std::__move_merge_adaptive(__buffer, __buffer_end, __middle, __last,
2426 				     __first, __comp);
2427 	}
2428       else if (__len2 <= __buffer_size)
2429 	{
2430 	  _Pointer __buffer_end = _GLIBCXX_MOVE3(__middle, __last, __buffer);
2431 	  std::__move_merge_adaptive_backward(__first, __middle, __buffer,
2432 					      __buffer_end, __last, __comp);
2433 	}
2434       else
2435 	{
2436 	  _BidirectionalIterator __first_cut = __first;
2437 	  _BidirectionalIterator __second_cut = __middle;
2438 	  _Distance __len11 = 0;
2439 	  _Distance __len22 = 0;
2440 	  if (__len1 > __len2)
2441 	    {
2442 	      __len11 = __len1 / 2;
2443 	      std::advance(__first_cut, __len11);
2444 	      __second_cut
2445 		= std::__lower_bound(__middle, __last, *__first_cut,
2446 				     __gnu_cxx::__ops::__iter_comp_val(__comp));
2447 	      __len22 = std::distance(__middle, __second_cut);
2448 	    }
2449 	  else
2450 	    {
2451 	      __len22 = __len2 / 2;
2452 	      std::advance(__second_cut, __len22);
2453 	      __first_cut
2454 		= std::__upper_bound(__first, __middle, *__second_cut,
2455 				     __gnu_cxx::__ops::__val_comp_iter(__comp));
2456 	      __len11 = std::distance(__first, __first_cut);
2457 	    }
2458 
2459 	  _BidirectionalIterator __new_middle
2460 	    = std::__rotate_adaptive(__first_cut, __middle, __second_cut,
2461 				     __len1 - __len11, __len22, __buffer,
2462 				     __buffer_size);
2463 	  std::__merge_adaptive(__first, __first_cut, __new_middle, __len11,
2464 				__len22, __buffer, __buffer_size, __comp);
2465 	  std::__merge_adaptive(__new_middle, __second_cut, __last,
2466 				__len1 - __len11,
2467 				__len2 - __len22, __buffer,
2468 				__buffer_size, __comp);
2469 	}
2470     }
2471 
2472   /// This is a helper function for the merge routines.
2473   template<typename _BidirectionalIterator, typename _Distance,
2474 	   typename _Compare>
2475     void
2476     __merge_without_buffer(_BidirectionalIterator __first,
2477 			   _BidirectionalIterator __middle,
2478 			   _BidirectionalIterator __last,
2479 			   _Distance __len1, _Distance __len2,
2480 			   _Compare __comp)
2481     {
2482       if (__len1 == 0 || __len2 == 0)
2483 	return;
2484 
2485       if (__len1 + __len2 == 2)
2486 	{
2487 	  if (__comp(__middle, __first))
2488 	    std::iter_swap(__first, __middle);
2489 	  return;
2490 	}
2491 
2492       _BidirectionalIterator __first_cut = __first;
2493       _BidirectionalIterator __second_cut = __middle;
2494       _Distance __len11 = 0;
2495       _Distance __len22 = 0;
2496       if (__len1 > __len2)
2497 	{
2498 	  __len11 = __len1 / 2;
2499 	  std::advance(__first_cut, __len11);
2500 	  __second_cut
2501 	    = std::__lower_bound(__middle, __last, *__first_cut,
2502 				 __gnu_cxx::__ops::__iter_comp_val(__comp));
2503 	  __len22 = std::distance(__middle, __second_cut);
2504 	}
2505       else
2506 	{
2507 	  __len22 = __len2 / 2;
2508 	  std::advance(__second_cut, __len22);
2509 	  __first_cut
2510 	    = std::__upper_bound(__first, __middle, *__second_cut,
2511 				 __gnu_cxx::__ops::__val_comp_iter(__comp));
2512 	  __len11 = std::distance(__first, __first_cut);
2513 	}
2514 
2515       std::rotate(__first_cut, __middle, __second_cut);
2516       _BidirectionalIterator __new_middle = __first_cut;
2517       std::advance(__new_middle, std::distance(__middle, __second_cut));
2518       std::__merge_without_buffer(__first, __first_cut, __new_middle,
2519 				  __len11, __len22, __comp);
2520       std::__merge_without_buffer(__new_middle, __second_cut, __last,
2521 				  __len1 - __len11, __len2 - __len22, __comp);
2522     }
2523 
2524   template<typename _BidirectionalIterator, typename _Compare>
2525     void
2526     __inplace_merge(_BidirectionalIterator __first,
2527 		    _BidirectionalIterator __middle,
2528 		    _BidirectionalIterator __last,
2529 		    _Compare __comp)
2530     {
2531       typedef typename iterator_traits<_BidirectionalIterator>::value_type
2532 	  _ValueType;
2533       typedef typename iterator_traits<_BidirectionalIterator>::difference_type
2534 	  _DistanceType;
2535 
2536       if (__first == __middle || __middle == __last)
2537 	return;
2538 
2539       const _DistanceType __len1 = std::distance(__first, __middle);
2540       const _DistanceType __len2 = std::distance(__middle, __last);
2541 
2542       typedef _Temporary_buffer<_BidirectionalIterator, _ValueType> _TmpBuf;
2543       _TmpBuf __buf(__first, __last);
2544 
2545       if (__buf.begin() == 0)
2546 	std::__merge_without_buffer
2547 	  (__first, __middle, __last, __len1, __len2, __comp);
2548       else
2549 	std::__merge_adaptive
2550 	  (__first, __middle, __last, __len1, __len2, __buf.begin(),
2551 	   _DistanceType(__buf.size()), __comp);
2552     }
2553 
2554   /**
2555    *  @brief Merges two sorted ranges in place.
2556    *  @ingroup sorting_algorithms
2557    *  @param  __first   An iterator.
2558    *  @param  __middle  Another iterator.
2559    *  @param  __last    Another iterator.
2560    *  @return  Nothing.
2561    *
2562    *  Merges two sorted and consecutive ranges, [__first,__middle) and
2563    *  [__middle,__last), and puts the result in [__first,__last).  The
2564    *  output will be sorted.  The sort is @e stable, that is, for
2565    *  equivalent elements in the two ranges, elements from the first
2566    *  range will always come before elements from the second.
2567    *
2568    *  If enough additional memory is available, this takes (__last-__first)-1
2569    *  comparisons.  Otherwise an NlogN algorithm is used, where N is
2570    *  distance(__first,__last).
2571   */
2572   template<typename _BidirectionalIterator>
2573     inline void
2574     inplace_merge(_BidirectionalIterator __first,
2575 		  _BidirectionalIterator __middle,
2576 		  _BidirectionalIterator __last)
2577     {
2578       // concept requirements
2579       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
2580 	    _BidirectionalIterator>)
2581       __glibcxx_function_requires(_LessThanComparableConcept<
2582 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
2583       __glibcxx_requires_sorted(__first, __middle);
2584       __glibcxx_requires_sorted(__middle, __last);
2585       __glibcxx_requires_irreflexive(__first, __last);
2586 
2587       std::__inplace_merge(__first, __middle, __last,
2588 			   __gnu_cxx::__ops::__iter_less_iter());
2589     }
2590 
2591   /**
2592    *  @brief Merges two sorted ranges in place.
2593    *  @ingroup sorting_algorithms
2594    *  @param  __first   An iterator.
2595    *  @param  __middle  Another iterator.
2596    *  @param  __last    Another iterator.
2597    *  @param  __comp    A functor to use for comparisons.
2598    *  @return  Nothing.
2599    *
2600    *  Merges two sorted and consecutive ranges, [__first,__middle) and
2601    *  [middle,last), and puts the result in [__first,__last).  The output will
2602    *  be sorted.  The sort is @e stable, that is, for equivalent
2603    *  elements in the two ranges, elements from the first range will always
2604    *  come before elements from the second.
2605    *
2606    *  If enough additional memory is available, this takes (__last-__first)-1
2607    *  comparisons.  Otherwise an NlogN algorithm is used, where N is
2608    *  distance(__first,__last).
2609    *
2610    *  The comparison function should have the same effects on ordering as
2611    *  the function used for the initial sort.
2612   */
2613   template<typename _BidirectionalIterator, typename _Compare>
2614     inline void
2615     inplace_merge(_BidirectionalIterator __first,
2616 		  _BidirectionalIterator __middle,
2617 		  _BidirectionalIterator __last,
2618 		  _Compare __comp)
2619     {
2620       // concept requirements
2621       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<
2622 	    _BidirectionalIterator>)
2623       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2624 	    typename iterator_traits<_BidirectionalIterator>::value_type,
2625 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
2626       __glibcxx_requires_sorted_pred(__first, __middle, __comp);
2627       __glibcxx_requires_sorted_pred(__middle, __last, __comp);
2628       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
2629 
2630       std::__inplace_merge(__first, __middle, __last,
2631 			   __gnu_cxx::__ops::__iter_comp_iter(__comp));
2632     }
2633 
2634 
2635   /// This is a helper function for the __merge_sort_loop routines.
2636   template<typename _InputIterator, typename _OutputIterator,
2637 	   typename _Compare>
2638     _OutputIterator
2639     __move_merge(_InputIterator __first1, _InputIterator __last1,
2640 		 _InputIterator __first2, _InputIterator __last2,
2641 		 _OutputIterator __result, _Compare __comp)
2642     {
2643       while (__first1 != __last1 && __first2 != __last2)
2644 	{
2645 	  if (__comp(__first2, __first1))
2646 	    {
2647 	      *__result = _GLIBCXX_MOVE(*__first2);
2648 	      ++__first2;
2649 	    }
2650 	  else
2651 	    {
2652 	      *__result = _GLIBCXX_MOVE(*__first1);
2653 	      ++__first1;
2654 	    }
2655 	  ++__result;
2656 	}
2657       return _GLIBCXX_MOVE3(__first2, __last2,
2658 			    _GLIBCXX_MOVE3(__first1, __last1,
2659 					   __result));
2660     }
2661 
2662   template<typename _RandomAccessIterator1, typename _RandomAccessIterator2,
2663 	   typename _Distance, typename _Compare>
2664     void
2665     __merge_sort_loop(_RandomAccessIterator1 __first,
2666 		      _RandomAccessIterator1 __last,
2667 		      _RandomAccessIterator2 __result, _Distance __step_size,
2668 		      _Compare __comp)
2669     {
2670       const _Distance __two_step = 2 * __step_size;
2671 
2672       while (__last - __first >= __two_step)
2673 	{
2674 	  __result = std::__move_merge(__first, __first + __step_size,
2675 				       __first + __step_size,
2676 				       __first + __two_step,
2677 				       __result, __comp);
2678 	  __first += __two_step;
2679 	}
2680       __step_size = std::min(_Distance(__last - __first), __step_size);
2681 
2682       std::__move_merge(__first, __first + __step_size,
2683 			__first + __step_size, __last, __result, __comp);
2684     }
2685 
2686   template<typename _RandomAccessIterator, typename _Distance,
2687 	   typename _Compare>
2688     void
2689     __chunk_insertion_sort(_RandomAccessIterator __first,
2690 			   _RandomAccessIterator __last,
2691 			   _Distance __chunk_size, _Compare __comp)
2692     {
2693       while (__last - __first >= __chunk_size)
2694 	{
2695 	  std::__insertion_sort(__first, __first + __chunk_size, __comp);
2696 	  __first += __chunk_size;
2697 	}
2698       std::__insertion_sort(__first, __last, __comp);
2699     }
2700 
2701   enum { _S_chunk_size = 7 };
2702 
2703   template<typename _RandomAccessIterator, typename _Pointer, typename _Compare>
2704     void
2705     __merge_sort_with_buffer(_RandomAccessIterator __first,
2706 			     _RandomAccessIterator __last,
2707 			     _Pointer __buffer, _Compare __comp)
2708     {
2709       typedef typename iterator_traits<_RandomAccessIterator>::difference_type
2710 	_Distance;
2711 
2712       const _Distance __len = __last - __first;
2713       const _Pointer __buffer_last = __buffer + __len;
2714 
2715       _Distance __step_size = _S_chunk_size;
2716       std::__chunk_insertion_sort(__first, __last, __step_size, __comp);
2717 
2718       while (__step_size < __len)
2719 	{
2720 	  std::__merge_sort_loop(__first, __last, __buffer,
2721 				 __step_size, __comp);
2722 	  __step_size *= 2;
2723 	  std::__merge_sort_loop(__buffer, __buffer_last, __first,
2724 				 __step_size, __comp);
2725 	  __step_size *= 2;
2726 	}
2727     }
2728 
2729   template<typename _RandomAccessIterator, typename _Pointer,
2730 	   typename _Distance, typename _Compare>
2731     void
2732     __stable_sort_adaptive(_RandomAccessIterator __first,
2733 			   _RandomAccessIterator __last,
2734 			   _Pointer __buffer, _Distance __buffer_size,
2735 			   _Compare __comp)
2736     {
2737       const _Distance __len = (__last - __first + 1) / 2;
2738       const _RandomAccessIterator __middle = __first + __len;
2739       if (__len > __buffer_size)
2740 	{
2741 	  std::__stable_sort_adaptive(__first, __middle, __buffer,
2742 				      __buffer_size, __comp);
2743 	  std::__stable_sort_adaptive(__middle, __last, __buffer,
2744 				      __buffer_size, __comp);
2745 	}
2746       else
2747 	{
2748 	  std::__merge_sort_with_buffer(__first, __middle, __buffer, __comp);
2749 	  std::__merge_sort_with_buffer(__middle, __last, __buffer, __comp);
2750 	}
2751       std::__merge_adaptive(__first, __middle, __last,
2752 			    _Distance(__middle - __first),
2753 			    _Distance(__last - __middle),
2754 			    __buffer, __buffer_size,
2755 			    __comp);
2756     }
2757 
2758   /// This is a helper function for the stable sorting routines.
2759   template<typename _RandomAccessIterator, typename _Compare>
2760     void
2761     __inplace_stable_sort(_RandomAccessIterator __first,
2762 			  _RandomAccessIterator __last, _Compare __comp)
2763     {
2764       if (__last - __first < 15)
2765 	{
2766 	  std::__insertion_sort(__first, __last, __comp);
2767 	  return;
2768 	}
2769       _RandomAccessIterator __middle = __first + (__last - __first) / 2;
2770       std::__inplace_stable_sort(__first, __middle, __comp);
2771       std::__inplace_stable_sort(__middle, __last, __comp);
2772       std::__merge_without_buffer(__first, __middle, __last,
2773 				  __middle - __first,
2774 				  __last - __middle,
2775 				  __comp);
2776     }
2777 
2778   // stable_sort
2779 
2780   // Set algorithms: includes, set_union, set_intersection, set_difference,
2781   // set_symmetric_difference.  All of these algorithms have the precondition
2782   // that their input ranges are sorted and the postcondition that their output
2783   // ranges are sorted.
2784 
2785   template<typename _InputIterator1, typename _InputIterator2,
2786 	   typename _Compare>
2787     bool
2788     __includes(_InputIterator1 __first1, _InputIterator1 __last1,
2789 	       _InputIterator2 __first2, _InputIterator2 __last2,
2790 	       _Compare __comp)
2791     {
2792       while (__first1 != __last1 && __first2 != __last2)
2793 	if (__comp(__first2, __first1))
2794 	  return false;
2795 	else if (__comp(__first1, __first2))
2796 	  ++__first1;
2797 	else
2798 	  {
2799 	    ++__first1;
2800 	    ++__first2;
2801 	  }
2802 
2803       return __first2 == __last2;
2804     }
2805 
2806   /**
2807    *  @brief Determines whether all elements of a sequence exists in a range.
2808    *  @param  __first1  Start of search range.
2809    *  @param  __last1   End of search range.
2810    *  @param  __first2  Start of sequence
2811    *  @param  __last2   End of sequence.
2812    *  @return  True if each element in [__first2,__last2) is contained in order
2813    *  within [__first1,__last1).  False otherwise.
2814    *  @ingroup set_algorithms
2815    *
2816    *  This operation expects both [__first1,__last1) and
2817    *  [__first2,__last2) to be sorted.  Searches for the presence of
2818    *  each element in [__first2,__last2) within [__first1,__last1).
2819    *  The iterators over each range only move forward, so this is a
2820    *  linear algorithm.  If an element in [__first2,__last2) is not
2821    *  found before the search iterator reaches @p __last2, false is
2822    *  returned.
2823   */
2824   template<typename _InputIterator1, typename _InputIterator2>
2825     inline bool
2826     includes(_InputIterator1 __first1, _InputIterator1 __last1,
2827 	     _InputIterator2 __first2, _InputIterator2 __last2)
2828     {
2829       // concept requirements
2830       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
2831       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
2832       __glibcxx_function_requires(_LessThanOpConcept<
2833 	    typename iterator_traits<_InputIterator1>::value_type,
2834 	    typename iterator_traits<_InputIterator2>::value_type>)
2835       __glibcxx_function_requires(_LessThanOpConcept<
2836 	    typename iterator_traits<_InputIterator2>::value_type,
2837 	    typename iterator_traits<_InputIterator1>::value_type>)
2838       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
2839       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
2840       __glibcxx_requires_irreflexive2(__first1, __last1);
2841       __glibcxx_requires_irreflexive2(__first2, __last2);
2842 
2843       return std::__includes(__first1, __last1, __first2, __last2,
2844 			     __gnu_cxx::__ops::__iter_less_iter());
2845     }
2846 
2847   /**
2848    *  @brief Determines whether all elements of a sequence exists in a range
2849    *  using comparison.
2850    *  @ingroup set_algorithms
2851    *  @param  __first1  Start of search range.
2852    *  @param  __last1   End of search range.
2853    *  @param  __first2  Start of sequence
2854    *  @param  __last2   End of sequence.
2855    *  @param  __comp    Comparison function to use.
2856    *  @return True if each element in [__first2,__last2) is contained
2857    *  in order within [__first1,__last1) according to comp.  False
2858    *  otherwise.  @ingroup set_algorithms
2859    *
2860    *  This operation expects both [__first1,__last1) and
2861    *  [__first2,__last2) to be sorted.  Searches for the presence of
2862    *  each element in [__first2,__last2) within [__first1,__last1),
2863    *  using comp to decide.  The iterators over each range only move
2864    *  forward, so this is a linear algorithm.  If an element in
2865    *  [__first2,__last2) is not found before the search iterator
2866    *  reaches @p __last2, false is returned.
2867   */
2868   template<typename _InputIterator1, typename _InputIterator2,
2869 	   typename _Compare>
2870     inline bool
2871     includes(_InputIterator1 __first1, _InputIterator1 __last1,
2872 	     _InputIterator2 __first2, _InputIterator2 __last2,
2873 	     _Compare __comp)
2874     {
2875       // concept requirements
2876       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
2877       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
2878       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2879 	    typename iterator_traits<_InputIterator1>::value_type,
2880 	    typename iterator_traits<_InputIterator2>::value_type>)
2881       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2882 	    typename iterator_traits<_InputIterator2>::value_type,
2883 	    typename iterator_traits<_InputIterator1>::value_type>)
2884       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
2885       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
2886       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
2887       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
2888 
2889       return std::__includes(__first1, __last1, __first2, __last2,
2890 			     __gnu_cxx::__ops::__iter_comp_iter(__comp));
2891     }
2892 
2893   // nth_element
2894   // merge
2895   // set_difference
2896   // set_intersection
2897   // set_union
2898   // stable_sort
2899   // set_symmetric_difference
2900   // min_element
2901   // max_element
2902 
2903   template<typename _BidirectionalIterator, typename _Compare>
2904     bool
2905     __next_permutation(_BidirectionalIterator __first,
2906 		       _BidirectionalIterator __last, _Compare __comp)
2907     {
2908       if (__first == __last)
2909 	return false;
2910       _BidirectionalIterator __i = __first;
2911       ++__i;
2912       if (__i == __last)
2913 	return false;
2914       __i = __last;
2915       --__i;
2916 
2917       for(;;)
2918 	{
2919 	  _BidirectionalIterator __ii = __i;
2920 	  --__i;
2921 	  if (__comp(__i, __ii))
2922 	    {
2923 	      _BidirectionalIterator __j = __last;
2924 	      while (!__comp(__i, --__j))
2925 		{}
2926 	      std::iter_swap(__i, __j);
2927 	      std::__reverse(__ii, __last,
2928 			     std::__iterator_category(__first));
2929 	      return true;
2930 	    }
2931 	  if (__i == __first)
2932 	    {
2933 	      std::__reverse(__first, __last,
2934 			     std::__iterator_category(__first));
2935 	      return false;
2936 	    }
2937 	}
2938     }
2939 
2940   /**
2941    *  @brief  Permute range into the next @e dictionary ordering.
2942    *  @ingroup sorting_algorithms
2943    *  @param  __first  Start of range.
2944    *  @param  __last   End of range.
2945    *  @return  False if wrapped to first permutation, true otherwise.
2946    *
2947    *  Treats all permutations of the range as a set of @e dictionary sorted
2948    *  sequences.  Permutes the current sequence into the next one of this set.
2949    *  Returns true if there are more sequences to generate.  If the sequence
2950    *  is the largest of the set, the smallest is generated and false returned.
2951   */
2952   template<typename _BidirectionalIterator>
2953     inline bool
2954     next_permutation(_BidirectionalIterator __first,
2955 		     _BidirectionalIterator __last)
2956     {
2957       // concept requirements
2958       __glibcxx_function_requires(_BidirectionalIteratorConcept<
2959 				  _BidirectionalIterator>)
2960       __glibcxx_function_requires(_LessThanComparableConcept<
2961 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
2962       __glibcxx_requires_valid_range(__first, __last);
2963       __glibcxx_requires_irreflexive(__first, __last);
2964 
2965       return std::__next_permutation
2966 	(__first, __last, __gnu_cxx::__ops::__iter_less_iter());
2967     }
2968 
2969   /**
2970    *  @brief  Permute range into the next @e dictionary ordering using
2971    *          comparison functor.
2972    *  @ingroup sorting_algorithms
2973    *  @param  __first  Start of range.
2974    *  @param  __last   End of range.
2975    *  @param  __comp   A comparison functor.
2976    *  @return  False if wrapped to first permutation, true otherwise.
2977    *
2978    *  Treats all permutations of the range [__first,__last) as a set of
2979    *  @e dictionary sorted sequences ordered by @p __comp.  Permutes the current
2980    *  sequence into the next one of this set.  Returns true if there are more
2981    *  sequences to generate.  If the sequence is the largest of the set, the
2982    *  smallest is generated and false returned.
2983   */
2984   template<typename _BidirectionalIterator, typename _Compare>
2985     inline bool
2986     next_permutation(_BidirectionalIterator __first,
2987 		     _BidirectionalIterator __last, _Compare __comp)
2988     {
2989       // concept requirements
2990       __glibcxx_function_requires(_BidirectionalIteratorConcept<
2991 				  _BidirectionalIterator>)
2992       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
2993 	    typename iterator_traits<_BidirectionalIterator>::value_type,
2994 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
2995       __glibcxx_requires_valid_range(__first, __last);
2996       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
2997 
2998       return std::__next_permutation
2999 	(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
3000     }
3001 
3002   template<typename _BidirectionalIterator, typename _Compare>
3003     bool
3004     __prev_permutation(_BidirectionalIterator __first,
3005 		       _BidirectionalIterator __last, _Compare __comp)
3006     {
3007       if (__first == __last)
3008 	return false;
3009       _BidirectionalIterator __i = __first;
3010       ++__i;
3011       if (__i == __last)
3012 	return false;
3013       __i = __last;
3014       --__i;
3015 
3016       for(;;)
3017 	{
3018 	  _BidirectionalIterator __ii = __i;
3019 	  --__i;
3020 	  if (__comp(__ii, __i))
3021 	    {
3022 	      _BidirectionalIterator __j = __last;
3023 	      while (!__comp(--__j, __i))
3024 		{}
3025 	      std::iter_swap(__i, __j);
3026 	      std::__reverse(__ii, __last,
3027 			     std::__iterator_category(__first));
3028 	      return true;
3029 	    }
3030 	  if (__i == __first)
3031 	    {
3032 	      std::__reverse(__first, __last,
3033 			     std::__iterator_category(__first));
3034 	      return false;
3035 	    }
3036 	}
3037     }
3038 
3039   /**
3040    *  @brief  Permute range into the previous @e dictionary ordering.
3041    *  @ingroup sorting_algorithms
3042    *  @param  __first  Start of range.
3043    *  @param  __last   End of range.
3044    *  @return  False if wrapped to last permutation, true otherwise.
3045    *
3046    *  Treats all permutations of the range as a set of @e dictionary sorted
3047    *  sequences.  Permutes the current sequence into the previous one of this
3048    *  set.  Returns true if there are more sequences to generate.  If the
3049    *  sequence is the smallest of the set, the largest is generated and false
3050    *  returned.
3051   */
3052   template<typename _BidirectionalIterator>
3053     inline bool
3054     prev_permutation(_BidirectionalIterator __first,
3055 		     _BidirectionalIterator __last)
3056     {
3057       // concept requirements
3058       __glibcxx_function_requires(_BidirectionalIteratorConcept<
3059 				  _BidirectionalIterator>)
3060       __glibcxx_function_requires(_LessThanComparableConcept<
3061 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
3062       __glibcxx_requires_valid_range(__first, __last);
3063       __glibcxx_requires_irreflexive(__first, __last);
3064 
3065       return std::__prev_permutation(__first, __last,
3066 				     __gnu_cxx::__ops::__iter_less_iter());
3067     }
3068 
3069   /**
3070    *  @brief  Permute range into the previous @e dictionary ordering using
3071    *          comparison functor.
3072    *  @ingroup sorting_algorithms
3073    *  @param  __first  Start of range.
3074    *  @param  __last   End of range.
3075    *  @param  __comp   A comparison functor.
3076    *  @return  False if wrapped to last permutation, true otherwise.
3077    *
3078    *  Treats all permutations of the range [__first,__last) as a set of
3079    *  @e dictionary sorted sequences ordered by @p __comp.  Permutes the current
3080    *  sequence into the previous one of this set.  Returns true if there are
3081    *  more sequences to generate.  If the sequence is the smallest of the set,
3082    *  the largest is generated and false returned.
3083   */
3084   template<typename _BidirectionalIterator, typename _Compare>
3085     inline bool
3086     prev_permutation(_BidirectionalIterator __first,
3087 		     _BidirectionalIterator __last, _Compare __comp)
3088     {
3089       // concept requirements
3090       __glibcxx_function_requires(_BidirectionalIteratorConcept<
3091 				  _BidirectionalIterator>)
3092       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3093 	    typename iterator_traits<_BidirectionalIterator>::value_type,
3094 	    typename iterator_traits<_BidirectionalIterator>::value_type>)
3095       __glibcxx_requires_valid_range(__first, __last);
3096       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3097 
3098       return std::__prev_permutation(__first, __last,
3099 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
3100     }
3101 
3102   // replace
3103   // replace_if
3104 
3105   template<typename _InputIterator, typename _OutputIterator,
3106 	   typename _Predicate, typename _Tp>
3107     _OutputIterator
3108     __replace_copy_if(_InputIterator __first, _InputIterator __last,
3109 		      _OutputIterator __result,
3110 		      _Predicate __pred, const _Tp& __new_value)
3111     {
3112       for (; __first != __last; ++__first, (void)++__result)
3113 	if (__pred(__first))
3114 	  *__result = __new_value;
3115 	else
3116 	  *__result = *__first;
3117       return __result;
3118     }
3119 
3120   /**
3121    *  @brief Copy a sequence, replacing each element of one value with another
3122    *         value.
3123    *  @param  __first      An input iterator.
3124    *  @param  __last       An input iterator.
3125    *  @param  __result     An output iterator.
3126    *  @param  __old_value  The value to be replaced.
3127    *  @param  __new_value  The replacement value.
3128    *  @return   The end of the output sequence, @p result+(last-first).
3129    *
3130    *  Copies each element in the input range @p [__first,__last) to the
3131    *  output range @p [__result,__result+(__last-__first)) replacing elements
3132    *  equal to @p __old_value with @p __new_value.
3133   */
3134   template<typename _InputIterator, typename _OutputIterator, typename _Tp>
3135     inline _OutputIterator
3136     replace_copy(_InputIterator __first, _InputIterator __last,
3137 		 _OutputIterator __result,
3138 		 const _Tp& __old_value, const _Tp& __new_value)
3139     {
3140       // concept requirements
3141       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3142       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
3143 	    typename iterator_traits<_InputIterator>::value_type>)
3144       __glibcxx_function_requires(_EqualOpConcept<
3145 	    typename iterator_traits<_InputIterator>::value_type, _Tp>)
3146       __glibcxx_requires_valid_range(__first, __last);
3147 
3148       return std::__replace_copy_if(__first, __last, __result,
3149 			__gnu_cxx::__ops::__iter_equals_val(__old_value),
3150 					      __new_value);
3151     }
3152 
3153   /**
3154    *  @brief Copy a sequence, replacing each value for which a predicate
3155    *         returns true with another value.
3156    *  @ingroup mutating_algorithms
3157    *  @param  __first      An input iterator.
3158    *  @param  __last       An input iterator.
3159    *  @param  __result     An output iterator.
3160    *  @param  __pred       A predicate.
3161    *  @param  __new_value  The replacement value.
3162    *  @return   The end of the output sequence, @p __result+(__last-__first).
3163    *
3164    *  Copies each element in the range @p [__first,__last) to the range
3165    *  @p [__result,__result+(__last-__first)) replacing elements for which
3166    *  @p __pred returns true with @p __new_value.
3167   */
3168   template<typename _InputIterator, typename _OutputIterator,
3169 	   typename _Predicate, typename _Tp>
3170     inline _OutputIterator
3171     replace_copy_if(_InputIterator __first, _InputIterator __last,
3172 		    _OutputIterator __result,
3173 		    _Predicate __pred, const _Tp& __new_value)
3174     {
3175       // concept requirements
3176       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3177       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
3178 	    typename iterator_traits<_InputIterator>::value_type>)
3179       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
3180 	    typename iterator_traits<_InputIterator>::value_type>)
3181       __glibcxx_requires_valid_range(__first, __last);
3182 
3183       return std::__replace_copy_if(__first, __last, __result,
3184 				__gnu_cxx::__ops::__pred_iter(__pred),
3185 					      __new_value);
3186     }
3187 
3188   template<typename _InputIterator, typename _Predicate>
3189     typename iterator_traits<_InputIterator>::difference_type
3190     __count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred)
3191     {
3192       typename iterator_traits<_InputIterator>::difference_type __n = 0;
3193       for (; __first != __last; ++__first)
3194 	if (__pred(__first))
3195 	  ++__n;
3196       return __n;
3197     }
3198 
3199 #if __cplusplus >= 201103L
3200   /**
3201    *  @brief  Determines whether the elements of a sequence are sorted.
3202    *  @ingroup sorting_algorithms
3203    *  @param  __first   An iterator.
3204    *  @param  __last    Another iterator.
3205    *  @return  True if the elements are sorted, false otherwise.
3206   */
3207   template<typename _ForwardIterator>
3208     inline bool
3209     is_sorted(_ForwardIterator __first, _ForwardIterator __last)
3210     { return std::is_sorted_until(__first, __last) == __last; }
3211 
3212   /**
3213    *  @brief  Determines whether the elements of a sequence are sorted
3214    *          according to a comparison functor.
3215    *  @ingroup sorting_algorithms
3216    *  @param  __first   An iterator.
3217    *  @param  __last    Another iterator.
3218    *  @param  __comp    A comparison functor.
3219    *  @return  True if the elements are sorted, false otherwise.
3220   */
3221   template<typename _ForwardIterator, typename _Compare>
3222     inline bool
3223     is_sorted(_ForwardIterator __first, _ForwardIterator __last,
3224 	      _Compare __comp)
3225     { return std::is_sorted_until(__first, __last, __comp) == __last; }
3226 
3227   template<typename _ForwardIterator, typename _Compare>
3228     _ForwardIterator
3229     __is_sorted_until(_ForwardIterator __first, _ForwardIterator __last,
3230 		      _Compare __comp)
3231     {
3232       if (__first == __last)
3233 	return __last;
3234 
3235       _ForwardIterator __next = __first;
3236       for (++__next; __next != __last; __first = __next, (void)++__next)
3237 	if (__comp(__next, __first))
3238 	  return __next;
3239       return __next;
3240     }
3241 
3242   /**
3243    *  @brief  Determines the end of a sorted sequence.
3244    *  @ingroup sorting_algorithms
3245    *  @param  __first   An iterator.
3246    *  @param  __last    Another iterator.
3247    *  @return  An iterator pointing to the last iterator i in [__first, __last)
3248    *           for which the range [__first, i) is sorted.
3249   */
3250   template<typename _ForwardIterator>
3251     inline _ForwardIterator
3252     is_sorted_until(_ForwardIterator __first, _ForwardIterator __last)
3253     {
3254       // concept requirements
3255       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3256       __glibcxx_function_requires(_LessThanComparableConcept<
3257 	    typename iterator_traits<_ForwardIterator>::value_type>)
3258       __glibcxx_requires_valid_range(__first, __last);
3259       __glibcxx_requires_irreflexive(__first, __last);
3260 
3261       return std::__is_sorted_until(__first, __last,
3262 				    __gnu_cxx::__ops::__iter_less_iter());
3263     }
3264 
3265   /**
3266    *  @brief  Determines the end of a sorted sequence using comparison functor.
3267    *  @ingroup sorting_algorithms
3268    *  @param  __first   An iterator.
3269    *  @param  __last    Another iterator.
3270    *  @param  __comp    A comparison functor.
3271    *  @return  An iterator pointing to the last iterator i in [__first, __last)
3272    *           for which the range [__first, i) is sorted.
3273   */
3274   template<typename _ForwardIterator, typename _Compare>
3275     inline _ForwardIterator
3276     is_sorted_until(_ForwardIterator __first, _ForwardIterator __last,
3277 		    _Compare __comp)
3278     {
3279       // concept requirements
3280       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3281       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3282 	    typename iterator_traits<_ForwardIterator>::value_type,
3283 	    typename iterator_traits<_ForwardIterator>::value_type>)
3284       __glibcxx_requires_valid_range(__first, __last);
3285       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3286 
3287       return std::__is_sorted_until(__first, __last,
3288 				    __gnu_cxx::__ops::__iter_comp_iter(__comp));
3289     }
3290 
3291   /**
3292    *  @brief  Determines min and max at once as an ordered pair.
3293    *  @ingroup sorting_algorithms
3294    *  @param  __a  A thing of arbitrary type.
3295    *  @param  __b  Another thing of arbitrary type.
3296    *  @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
3297    *  __b) otherwise.
3298   */
3299   template<typename _Tp>
3300     _GLIBCXX14_CONSTEXPR
3301     inline pair<const _Tp&, const _Tp&>
3302     minmax(const _Tp& __a, const _Tp& __b)
3303     {
3304       // concept requirements
3305       __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
3306 
3307       return __b < __a ? pair<const _Tp&, const _Tp&>(__b, __a)
3308 		       : pair<const _Tp&, const _Tp&>(__a, __b);
3309     }
3310 
3311   /**
3312    *  @brief  Determines min and max at once as an ordered pair.
3313    *  @ingroup sorting_algorithms
3314    *  @param  __a  A thing of arbitrary type.
3315    *  @param  __b  Another thing of arbitrary type.
3316    *  @param  __comp  A @link comparison_functors comparison functor @endlink.
3317    *  @return A pair(__b, __a) if __b is smaller than __a, pair(__a,
3318    *  __b) otherwise.
3319   */
3320   template<typename _Tp, typename _Compare>
3321     _GLIBCXX14_CONSTEXPR
3322     inline pair<const _Tp&, const _Tp&>
3323     minmax(const _Tp& __a, const _Tp& __b, _Compare __comp)
3324     {
3325       return __comp(__b, __a) ? pair<const _Tp&, const _Tp&>(__b, __a)
3326 			      : pair<const _Tp&, const _Tp&>(__a, __b);
3327     }
3328 
3329   template<typename _ForwardIterator, typename _Compare>
3330     _GLIBCXX14_CONSTEXPR
3331     pair<_ForwardIterator, _ForwardIterator>
3332     __minmax_element(_ForwardIterator __first, _ForwardIterator __last,
3333 		     _Compare __comp)
3334     {
3335       _ForwardIterator __next = __first;
3336       if (__first == __last
3337 	  || ++__next == __last)
3338 	return std::make_pair(__first, __first);
3339 
3340       _ForwardIterator __min{}, __max{};
3341       if (__comp(__next, __first))
3342 	{
3343 	  __min = __next;
3344 	  __max = __first;
3345 	}
3346       else
3347 	{
3348 	  __min = __first;
3349 	  __max = __next;
3350 	}
3351 
3352       __first = __next;
3353       ++__first;
3354 
3355       while (__first != __last)
3356 	{
3357 	  __next = __first;
3358 	  if (++__next == __last)
3359 	    {
3360 	      if (__comp(__first, __min))
3361 		__min = __first;
3362 	      else if (!__comp(__first, __max))
3363 		__max = __first;
3364 	      break;
3365 	    }
3366 
3367 	  if (__comp(__next, __first))
3368 	    {
3369 	      if (__comp(__next, __min))
3370 		__min = __next;
3371 	      if (!__comp(__first, __max))
3372 		__max = __first;
3373 	    }
3374 	  else
3375 	    {
3376 	      if (__comp(__first, __min))
3377 		__min = __first;
3378 	      if (!__comp(__next, __max))
3379 		__max = __next;
3380 	    }
3381 
3382 	  __first = __next;
3383 	  ++__first;
3384 	}
3385 
3386       return std::make_pair(__min, __max);
3387     }
3388 
3389   /**
3390    *  @brief  Return a pair of iterators pointing to the minimum and maximum
3391    *          elements in a range.
3392    *  @ingroup sorting_algorithms
3393    *  @param  __first  Start of range.
3394    *  @param  __last   End of range.
3395    *  @return  make_pair(m, M), where m is the first iterator i in
3396    *           [__first, __last) such that no other element in the range is
3397    *           smaller, and where M is the last iterator i in [__first, __last)
3398    *           such that no other element in the range is larger.
3399   */
3400   template<typename _ForwardIterator>
3401     _GLIBCXX14_CONSTEXPR
3402     inline pair<_ForwardIterator, _ForwardIterator>
3403     minmax_element(_ForwardIterator __first, _ForwardIterator __last)
3404     {
3405       // concept requirements
3406       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3407       __glibcxx_function_requires(_LessThanComparableConcept<
3408 	    typename iterator_traits<_ForwardIterator>::value_type>)
3409       __glibcxx_requires_valid_range(__first, __last);
3410       __glibcxx_requires_irreflexive(__first, __last);
3411 
3412       return std::__minmax_element(__first, __last,
3413 				   __gnu_cxx::__ops::__iter_less_iter());
3414     }
3415 
3416   /**
3417    *  @brief  Return a pair of iterators pointing to the minimum and maximum
3418    *          elements in a range.
3419    *  @ingroup sorting_algorithms
3420    *  @param  __first  Start of range.
3421    *  @param  __last   End of range.
3422    *  @param  __comp   Comparison functor.
3423    *  @return  make_pair(m, M), where m is the first iterator i in
3424    *           [__first, __last) such that no other element in the range is
3425    *           smaller, and where M is the last iterator i in [__first, __last)
3426    *           such that no other element in the range is larger.
3427   */
3428   template<typename _ForwardIterator, typename _Compare>
3429     _GLIBCXX14_CONSTEXPR
3430     inline pair<_ForwardIterator, _ForwardIterator>
3431     minmax_element(_ForwardIterator __first, _ForwardIterator __last,
3432 		   _Compare __comp)
3433     {
3434       // concept requirements
3435       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3436       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
3437 	    typename iterator_traits<_ForwardIterator>::value_type,
3438 	    typename iterator_traits<_ForwardIterator>::value_type>)
3439       __glibcxx_requires_valid_range(__first, __last);
3440       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
3441 
3442       return std::__minmax_element(__first, __last,
3443 				   __gnu_cxx::__ops::__iter_comp_iter(__comp));
3444     }
3445 
3446   // N2722 + DR 915.
3447   template<typename _Tp>
3448     _GLIBCXX14_CONSTEXPR
3449     inline _Tp
3450     min(initializer_list<_Tp> __l)
3451     { return *std::min_element(__l.begin(), __l.end()); }
3452 
3453   template<typename _Tp, typename _Compare>
3454     _GLIBCXX14_CONSTEXPR
3455     inline _Tp
3456     min(initializer_list<_Tp> __l, _Compare __comp)
3457     { return *std::min_element(__l.begin(), __l.end(), __comp); }
3458 
3459   template<typename _Tp>
3460     _GLIBCXX14_CONSTEXPR
3461     inline _Tp
3462     max(initializer_list<_Tp> __l)
3463     { return *std::max_element(__l.begin(), __l.end()); }
3464 
3465   template<typename _Tp, typename _Compare>
3466     _GLIBCXX14_CONSTEXPR
3467     inline _Tp
3468     max(initializer_list<_Tp> __l, _Compare __comp)
3469     { return *std::max_element(__l.begin(), __l.end(), __comp); }
3470 
3471   template<typename _Tp>
3472     _GLIBCXX14_CONSTEXPR
3473     inline pair<_Tp, _Tp>
3474     minmax(initializer_list<_Tp> __l)
3475     {
3476       pair<const _Tp*, const _Tp*> __p =
3477 	std::minmax_element(__l.begin(), __l.end());
3478       return std::make_pair(*__p.first, *__p.second);
3479     }
3480 
3481   template<typename _Tp, typename _Compare>
3482     _GLIBCXX14_CONSTEXPR
3483     inline pair<_Tp, _Tp>
3484     minmax(initializer_list<_Tp> __l, _Compare __comp)
3485     {
3486       pair<const _Tp*, const _Tp*> __p =
3487 	std::minmax_element(__l.begin(), __l.end(), __comp);
3488       return std::make_pair(*__p.first, *__p.second);
3489     }
3490 
3491   template<typename _ForwardIterator1, typename _ForwardIterator2,
3492 	   typename _BinaryPredicate>
3493     bool
3494     __is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3495 		     _ForwardIterator2 __first2, _BinaryPredicate __pred)
3496     {
3497       // Efficiently compare identical prefixes:  O(N) if sequences
3498       // have the same elements in the same order.
3499       for (; __first1 != __last1; ++__first1, (void)++__first2)
3500 	if (!__pred(__first1, __first2))
3501 	  break;
3502 
3503       if (__first1 == __last1)
3504 	return true;
3505 
3506       // Establish __last2 assuming equal ranges by iterating over the
3507       // rest of the list.
3508       _ForwardIterator2 __last2 = __first2;
3509       std::advance(__last2, std::distance(__first1, __last1));
3510       for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
3511 	{
3512 	  if (__scan != std::__find_if(__first1, __scan,
3513 			  __gnu_cxx::__ops::__iter_comp_iter(__pred, __scan)))
3514 	    continue; // We've seen this one before.
3515 
3516 	  auto __matches
3517 	    = std::__count_if(__first2, __last2,
3518 			__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan));
3519 	  if (0 == __matches ||
3520 	      std::__count_if(__scan, __last1,
3521 			__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan))
3522 	      != __matches)
3523 	    return false;
3524 	}
3525       return true;
3526     }
3527 
3528   /**
3529    *  @brief  Checks whether a permutation of the second sequence is equal
3530    *          to the first sequence.
3531    *  @ingroup non_mutating_algorithms
3532    *  @param  __first1  Start of first range.
3533    *  @param  __last1   End of first range.
3534    *  @param  __first2  Start of second range.
3535    *  @return true if there exists a permutation of the elements in the range
3536    *          [__first2, __first2 + (__last1 - __first1)), beginning with
3537    *          ForwardIterator2 begin, such that equal(__first1, __last1, begin)
3538    *          returns true; otherwise, returns false.
3539   */
3540   template<typename _ForwardIterator1, typename _ForwardIterator2>
3541     inline bool
3542     is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3543 		   _ForwardIterator2 __first2)
3544     {
3545       // concept requirements
3546       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
3547       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
3548       __glibcxx_function_requires(_EqualOpConcept<
3549 		typename iterator_traits<_ForwardIterator1>::value_type,
3550 		typename iterator_traits<_ForwardIterator2>::value_type>)
3551       __glibcxx_requires_valid_range(__first1, __last1);
3552 
3553       return std::__is_permutation(__first1, __last1, __first2,
3554 				   __gnu_cxx::__ops::__iter_equal_to_iter());
3555     }
3556 
3557   /**
3558    *  @brief  Checks whether a permutation of the second sequence is equal
3559    *          to the first sequence.
3560    *  @ingroup non_mutating_algorithms
3561    *  @param  __first1  Start of first range.
3562    *  @param  __last1   End of first range.
3563    *  @param  __first2  Start of second range.
3564    *  @param  __pred    A binary predicate.
3565    *  @return true if there exists a permutation of the elements in
3566    *          the range [__first2, __first2 + (__last1 - __first1)),
3567    *          beginning with ForwardIterator2 begin, such that
3568    *          equal(__first1, __last1, __begin, __pred) returns true;
3569    *          otherwise, returns false.
3570   */
3571   template<typename _ForwardIterator1, typename _ForwardIterator2,
3572 	   typename _BinaryPredicate>
3573     inline bool
3574     is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3575 		   _ForwardIterator2 __first2, _BinaryPredicate __pred)
3576     {
3577       // concept requirements
3578       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
3579       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
3580       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
3581 	    typename iterator_traits<_ForwardIterator1>::value_type,
3582 	    typename iterator_traits<_ForwardIterator2>::value_type>)
3583       __glibcxx_requires_valid_range(__first1, __last1);
3584 
3585       return std::__is_permutation(__first1, __last1, __first2,
3586 				   __gnu_cxx::__ops::__iter_comp_iter(__pred));
3587     }
3588 
3589 #if __cplusplus > 201103L
3590   template<typename _ForwardIterator1, typename _ForwardIterator2,
3591 	   typename _BinaryPredicate>
3592     bool
3593     __is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3594 		     _ForwardIterator2 __first2, _ForwardIterator2 __last2,
3595 		     _BinaryPredicate __pred)
3596     {
3597       using _Cat1
3598 	= typename iterator_traits<_ForwardIterator1>::iterator_category;
3599       using _Cat2
3600 	= typename iterator_traits<_ForwardIterator2>::iterator_category;
3601       using _It1_is_RA = is_same<_Cat1, random_access_iterator_tag>;
3602       using _It2_is_RA = is_same<_Cat2, random_access_iterator_tag>;
3603       constexpr bool __ra_iters = _It1_is_RA() && _It2_is_RA();
3604       if (__ra_iters)
3605 	{
3606 	  auto __d1 = std::distance(__first1, __last1);
3607 	  auto __d2 = std::distance(__first2, __last2);
3608 	  if (__d1 != __d2)
3609 	    return false;
3610 	}
3611 
3612       // Efficiently compare identical prefixes:  O(N) if sequences
3613       // have the same elements in the same order.
3614       for (; __first1 != __last1 && __first2 != __last2;
3615 	  ++__first1, (void)++__first2)
3616 	if (!__pred(__first1, __first2))
3617 	  break;
3618 
3619       if (__ra_iters)
3620 	{
3621 	  if (__first1 == __last1)
3622 	    return true;
3623 	}
3624       else
3625 	{
3626 	  auto __d1 = std::distance(__first1, __last1);
3627 	  auto __d2 = std::distance(__first2, __last2);
3628 	  if (__d1 == 0 && __d2 == 0)
3629 	    return true;
3630 	  if (__d1 != __d2)
3631 	    return false;
3632 	}
3633 
3634       for (_ForwardIterator1 __scan = __first1; __scan != __last1; ++__scan)
3635 	{
3636 	  if (__scan != std::__find_if(__first1, __scan,
3637 			__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan)))
3638 	    continue; // We've seen this one before.
3639 
3640 	  auto __matches = std::__count_if(__first2, __last2,
3641 		__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan));
3642 	  if (0 == __matches
3643 	      || std::__count_if(__scan, __last1,
3644 			__gnu_cxx::__ops::__iter_comp_iter(__pred, __scan))
3645 	      != __matches)
3646 	    return false;
3647 	}
3648       return true;
3649     }
3650 
3651   /**
3652    *  @brief  Checks whether a permutaion of the second sequence is equal
3653    *          to the first sequence.
3654    *  @ingroup non_mutating_algorithms
3655    *  @param  __first1  Start of first range.
3656    *  @param  __last1   End of first range.
3657    *  @param  __first2  Start of second range.
3658    *  @param  __last2   End of first range.
3659    *  @return true if there exists a permutation of the elements in the range
3660    *          [__first2, __last2), beginning with ForwardIterator2 begin,
3661    *          such that equal(__first1, __last1, begin) returns true;
3662    *          otherwise, returns false.
3663   */
3664   template<typename _ForwardIterator1, typename _ForwardIterator2>
3665     inline bool
3666     is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3667 		   _ForwardIterator2 __first2, _ForwardIterator2 __last2)
3668     {
3669       __glibcxx_requires_valid_range(__first1, __last1);
3670       __glibcxx_requires_valid_range(__first2, __last2);
3671 
3672       return
3673 	std::__is_permutation(__first1, __last1, __first2, __last2,
3674 			      __gnu_cxx::__ops::__iter_equal_to_iter());
3675     }
3676 
3677   /**
3678    *  @brief  Checks whether a permutation of the second sequence is equal
3679    *          to the first sequence.
3680    *  @ingroup non_mutating_algorithms
3681    *  @param  __first1  Start of first range.
3682    *  @param  __last1   End of first range.
3683    *  @param  __first2  Start of second range.
3684    *  @param  __last2   End of first range.
3685    *  @param  __pred    A binary predicate.
3686    *  @return true if there exists a permutation of the elements in the range
3687    *          [__first2, __last2), beginning with ForwardIterator2 begin,
3688    *          such that equal(__first1, __last1, __begin, __pred) returns true;
3689    *          otherwise, returns false.
3690   */
3691   template<typename _ForwardIterator1, typename _ForwardIterator2,
3692 	   typename _BinaryPredicate>
3693     inline bool
3694     is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
3695 		   _ForwardIterator2 __first2, _ForwardIterator2 __last2,
3696 		   _BinaryPredicate __pred)
3697     {
3698       __glibcxx_requires_valid_range(__first1, __last1);
3699       __glibcxx_requires_valid_range(__first2, __last2);
3700 
3701       return std::__is_permutation(__first1, __last1, __first2, __last2,
3702 				   __gnu_cxx::__ops::__iter_comp_iter(__pred));
3703     }
3704 
3705 #if __cplusplus > 201402L
3706 
3707 #define __cpp_lib_clamp 201603
3708 
3709   /**
3710    *  @brief  Returns the value clamped between lo and hi.
3711    *  @ingroup sorting_algorithms
3712    *  @param  __val  A value of arbitrary type.
3713    *  @param  __lo   A lower limit of arbitrary type.
3714    *  @param  __hi   An upper limit of arbitrary type.
3715    *  @return max(__val, __lo) if __val < __hi or min(__val, __hi) otherwise.
3716    */
3717   template<typename _Tp>
3718     constexpr const _Tp&
3719     clamp(const _Tp& __val, const _Tp& __lo, const _Tp& __hi)
3720     {
3721       __glibcxx_assert(!(__hi < __lo));
3722       return (__val < __lo) ? __lo : (__hi < __val) ? __hi : __val;
3723     }
3724 
3725   /**
3726    *  @brief  Returns the value clamped between lo and hi.
3727    *  @ingroup sorting_algorithms
3728    *  @param  __val   A value of arbitrary type.
3729    *  @param  __lo    A lower limit of arbitrary type.
3730    *  @param  __hi    An upper limit of arbitrary type.
3731    *  @param  __comp  A comparison functor.
3732    *  @return max(__val, __lo, __comp) if __comp(__val, __hi)
3733    *	      or min(__val, __hi, __comp) otherwise.
3734    */
3735   template<typename _Tp, typename _Compare>
3736     constexpr const _Tp&
3737     clamp(const _Tp& __val, const _Tp& __lo, const _Tp& __hi, _Compare __comp)
3738     {
3739       __glibcxx_assert(!__comp(__hi, __lo));
3740       return __comp(__val, __lo) ? __lo : __comp(__hi, __val) ? __hi : __val;
3741     }
3742 #endif // C++17
3743 #endif // C++14
3744 
3745 #ifdef _GLIBCXX_USE_C99_STDINT_TR1
3746   /**
3747    *  @brief Generate two uniformly distributed integers using a
3748    *         single distribution invocation.
3749    *  @param  __b0    The upper bound for the first integer.
3750    *  @param  __b1    The upper bound for the second integer.
3751    *  @param  __g     A UniformRandomBitGenerator.
3752    *  @return  A pair (i, j) with i and j uniformly distributed
3753    *           over [0, __b0) and [0, __b1), respectively.
3754    *
3755    *  Requires: __b0 * __b1 <= __g.max() - __g.min().
3756    *
3757    *  Using uniform_int_distribution with a range that is very
3758    *  small relative to the range of the generator ends up wasting
3759    *  potentially expensively generated randomness, since
3760    *  uniform_int_distribution does not store leftover randomness
3761    *  between invocations.
3762    *
3763    *  If we know we want two integers in ranges that are sufficiently
3764    *  small, we can compose the ranges, use a single distribution
3765    *  invocation, and significantly reduce the waste.
3766   */
3767   template<typename _IntType, typename _UniformRandomBitGenerator>
3768     pair<_IntType, _IntType>
3769     __gen_two_uniform_ints(_IntType __b0, _IntType __b1,
3770 			   _UniformRandomBitGenerator&& __g)
3771     {
3772       _IntType __x
3773 	= uniform_int_distribution<_IntType>{0, (__b0 * __b1) - 1}(__g);
3774       return std::make_pair(__x / __b1, __x % __b1);
3775     }
3776 
3777   /**
3778    *  @brief Shuffle the elements of a sequence using a uniform random
3779    *         number generator.
3780    *  @ingroup mutating_algorithms
3781    *  @param  __first   A forward iterator.
3782    *  @param  __last    A forward iterator.
3783    *  @param  __g       A UniformRandomNumberGenerator (26.5.1.3).
3784    *  @return  Nothing.
3785    *
3786    *  Reorders the elements in the range @p [__first,__last) using @p __g to
3787    *  provide random numbers.
3788   */
3789   template<typename _RandomAccessIterator,
3790 	   typename _UniformRandomNumberGenerator>
3791     void
3792     shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
3793 	    _UniformRandomNumberGenerator&& __g)
3794     {
3795       // concept requirements
3796       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
3797 	    _RandomAccessIterator>)
3798       __glibcxx_requires_valid_range(__first, __last);
3799 
3800       if (__first == __last)
3801 	return;
3802 
3803       typedef typename iterator_traits<_RandomAccessIterator>::difference_type
3804 	_DistanceType;
3805 
3806       typedef typename std::make_unsigned<_DistanceType>::type __ud_type;
3807       typedef typename std::uniform_int_distribution<__ud_type> __distr_type;
3808       typedef typename __distr_type::param_type __p_type;
3809 
3810       typedef typename remove_reference<_UniformRandomNumberGenerator>::type
3811 	_Gen;
3812       typedef typename common_type<typename _Gen::result_type, __ud_type>::type
3813 	__uc_type;
3814 
3815       const __uc_type __urngrange = __g.max() - __g.min();
3816       const __uc_type __urange = __uc_type(__last - __first);
3817 
3818       if (__urngrange / __urange >= __urange)
3819         // I.e. (__urngrange >= __urange * __urange) but without wrap issues.
3820       {
3821 	_RandomAccessIterator __i = __first + 1;
3822 
3823 	// Since we know the range isn't empty, an even number of elements
3824 	// means an uneven number of elements /to swap/, in which case we
3825 	// do the first one up front:
3826 
3827 	if ((__urange % 2) == 0)
3828 	{
3829 	  __distr_type __d{0, 1};
3830 	  std::iter_swap(__i++, __first + __d(__g));
3831 	}
3832 
3833 	// Now we know that __last - __i is even, so we do the rest in pairs,
3834 	// using a single distribution invocation to produce swap positions
3835 	// for two successive elements at a time:
3836 
3837 	while (__i != __last)
3838 	{
3839 	  const __uc_type __swap_range = __uc_type(__i - __first) + 1;
3840 
3841 	  const pair<__uc_type, __uc_type> __pospos =
3842 	    __gen_two_uniform_ints(__swap_range, __swap_range + 1, __g);
3843 
3844 	  std::iter_swap(__i++, __first + __pospos.first);
3845 	  std::iter_swap(__i++, __first + __pospos.second);
3846 	}
3847 
3848 	return;
3849       }
3850 
3851       __distr_type __d;
3852 
3853       for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
3854 	std::iter_swap(__i, __first + __d(__g, __p_type(0, __i - __first)));
3855     }
3856 #endif
3857 
3858 #endif // C++11
3859 
3860 _GLIBCXX_BEGIN_NAMESPACE_ALGO
3861 
3862   /**
3863    *  @brief Apply a function to every element of a sequence.
3864    *  @ingroup non_mutating_algorithms
3865    *  @param  __first  An input iterator.
3866    *  @param  __last   An input iterator.
3867    *  @param  __f      A unary function object.
3868    *  @return   @p __f
3869    *
3870    *  Applies the function object @p __f to each element in the range
3871    *  @p [first,last).  @p __f must not modify the order of the sequence.
3872    *  If @p __f has a return value it is ignored.
3873   */
3874   template<typename _InputIterator, typename _Function>
3875     _Function
3876     for_each(_InputIterator __first, _InputIterator __last, _Function __f)
3877     {
3878       // concept requirements
3879       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3880       __glibcxx_requires_valid_range(__first, __last);
3881       for (; __first != __last; ++__first)
3882 	__f(*__first);
3883       return __f; // N.B. [alg.foreach] says std::move(f) but it's redundant.
3884     }
3885 
3886   /**
3887    *  @brief Find the first occurrence of a value in a sequence.
3888    *  @ingroup non_mutating_algorithms
3889    *  @param  __first  An input iterator.
3890    *  @param  __last   An input iterator.
3891    *  @param  __val    The value to find.
3892    *  @return   The first iterator @c i in the range @p [__first,__last)
3893    *  such that @c *i == @p __val, or @p __last if no such iterator exists.
3894   */
3895   template<typename _InputIterator, typename _Tp>
3896     inline _InputIterator
3897     find(_InputIterator __first, _InputIterator __last,
3898 	 const _Tp& __val)
3899     {
3900       // concept requirements
3901       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3902       __glibcxx_function_requires(_EqualOpConcept<
3903 		typename iterator_traits<_InputIterator>::value_type, _Tp>)
3904       __glibcxx_requires_valid_range(__first, __last);
3905       return std::__find_if(__first, __last,
3906 			    __gnu_cxx::__ops::__iter_equals_val(__val));
3907     }
3908 
3909   /**
3910    *  @brief Find the first element in a sequence for which a
3911    *         predicate is true.
3912    *  @ingroup non_mutating_algorithms
3913    *  @param  __first  An input iterator.
3914    *  @param  __last   An input iterator.
3915    *  @param  __pred   A predicate.
3916    *  @return   The first iterator @c i in the range @p [__first,__last)
3917    *  such that @p __pred(*i) is true, or @p __last if no such iterator exists.
3918   */
3919   template<typename _InputIterator, typename _Predicate>
3920     inline _InputIterator
3921     find_if(_InputIterator __first, _InputIterator __last,
3922 	    _Predicate __pred)
3923     {
3924       // concept requirements
3925       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3926       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
3927 	      typename iterator_traits<_InputIterator>::value_type>)
3928       __glibcxx_requires_valid_range(__first, __last);
3929 
3930       return std::__find_if(__first, __last,
3931 			    __gnu_cxx::__ops::__pred_iter(__pred));
3932     }
3933 
3934   /**
3935    *  @brief  Find element from a set in a sequence.
3936    *  @ingroup non_mutating_algorithms
3937    *  @param  __first1  Start of range to search.
3938    *  @param  __last1   End of range to search.
3939    *  @param  __first2  Start of match candidates.
3940    *  @param  __last2   End of match candidates.
3941    *  @return   The first iterator @c i in the range
3942    *  @p [__first1,__last1) such that @c *i == @p *(i2) such that i2 is an
3943    *  iterator in [__first2,__last2), or @p __last1 if no such iterator exists.
3944    *
3945    *  Searches the range @p [__first1,__last1) for an element that is
3946    *  equal to some element in the range [__first2,__last2).  If
3947    *  found, returns an iterator in the range [__first1,__last1),
3948    *  otherwise returns @p __last1.
3949   */
3950   template<typename _InputIterator, typename _ForwardIterator>
3951     _InputIterator
3952     find_first_of(_InputIterator __first1, _InputIterator __last1,
3953 		  _ForwardIterator __first2, _ForwardIterator __last2)
3954     {
3955       // concept requirements
3956       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3957       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
3958       __glibcxx_function_requires(_EqualOpConcept<
3959 	    typename iterator_traits<_InputIterator>::value_type,
3960 	    typename iterator_traits<_ForwardIterator>::value_type>)
3961       __glibcxx_requires_valid_range(__first1, __last1);
3962       __glibcxx_requires_valid_range(__first2, __last2);
3963 
3964       for (; __first1 != __last1; ++__first1)
3965 	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
3966 	  if (*__first1 == *__iter)
3967 	    return __first1;
3968       return __last1;
3969     }
3970 
3971   /**
3972    *  @brief  Find element from a set in a sequence using a predicate.
3973    *  @ingroup non_mutating_algorithms
3974    *  @param  __first1  Start of range to search.
3975    *  @param  __last1   End of range to search.
3976    *  @param  __first2  Start of match candidates.
3977    *  @param  __last2   End of match candidates.
3978    *  @param  __comp    Predicate to use.
3979    *  @return   The first iterator @c i in the range
3980    *  @p [__first1,__last1) such that @c comp(*i, @p *(i2)) is true
3981    *  and i2 is an iterator in [__first2,__last2), or @p __last1 if no
3982    *  such iterator exists.
3983    *
3984 
3985    *  Searches the range @p [__first1,__last1) for an element that is
3986    *  equal to some element in the range [__first2,__last2).  If
3987    *  found, returns an iterator in the range [__first1,__last1),
3988    *  otherwise returns @p __last1.
3989   */
3990   template<typename _InputIterator, typename _ForwardIterator,
3991 	   typename _BinaryPredicate>
3992     _InputIterator
3993     find_first_of(_InputIterator __first1, _InputIterator __last1,
3994 		  _ForwardIterator __first2, _ForwardIterator __last2,
3995 		  _BinaryPredicate __comp)
3996     {
3997       // concept requirements
3998       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
3999       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4000       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4001 	    typename iterator_traits<_InputIterator>::value_type,
4002 	    typename iterator_traits<_ForwardIterator>::value_type>)
4003       __glibcxx_requires_valid_range(__first1, __last1);
4004       __glibcxx_requires_valid_range(__first2, __last2);
4005 
4006       for (; __first1 != __last1; ++__first1)
4007 	for (_ForwardIterator __iter = __first2; __iter != __last2; ++__iter)
4008 	  if (__comp(*__first1, *__iter))
4009 	    return __first1;
4010       return __last1;
4011     }
4012 
4013   /**
4014    *  @brief Find two adjacent values in a sequence that are equal.
4015    *  @ingroup non_mutating_algorithms
4016    *  @param  __first  A forward iterator.
4017    *  @param  __last   A forward iterator.
4018    *  @return   The first iterator @c i such that @c i and @c i+1 are both
4019    *  valid iterators in @p [__first,__last) and such that @c *i == @c *(i+1),
4020    *  or @p __last if no such iterator exists.
4021   */
4022   template<typename _ForwardIterator>
4023     inline _ForwardIterator
4024     adjacent_find(_ForwardIterator __first, _ForwardIterator __last)
4025     {
4026       // concept requirements
4027       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4028       __glibcxx_function_requires(_EqualityComparableConcept<
4029 	    typename iterator_traits<_ForwardIterator>::value_type>)
4030       __glibcxx_requires_valid_range(__first, __last);
4031 
4032       return std::__adjacent_find(__first, __last,
4033 				  __gnu_cxx::__ops::__iter_equal_to_iter());
4034     }
4035 
4036   /**
4037    *  @brief Find two adjacent values in a sequence using a predicate.
4038    *  @ingroup non_mutating_algorithms
4039    *  @param  __first         A forward iterator.
4040    *  @param  __last          A forward iterator.
4041    *  @param  __binary_pred   A binary predicate.
4042    *  @return   The first iterator @c i such that @c i and @c i+1 are both
4043    *  valid iterators in @p [__first,__last) and such that
4044    *  @p __binary_pred(*i,*(i+1)) is true, or @p __last if no such iterator
4045    *  exists.
4046   */
4047   template<typename _ForwardIterator, typename _BinaryPredicate>
4048     inline _ForwardIterator
4049     adjacent_find(_ForwardIterator __first, _ForwardIterator __last,
4050 		  _BinaryPredicate __binary_pred)
4051     {
4052       // concept requirements
4053       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4054       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4055 	    typename iterator_traits<_ForwardIterator>::value_type,
4056 	    typename iterator_traits<_ForwardIterator>::value_type>)
4057       __glibcxx_requires_valid_range(__first, __last);
4058 
4059       return std::__adjacent_find(__first, __last,
4060 			__gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
4061     }
4062 
4063   /**
4064    *  @brief Count the number of copies of a value in a sequence.
4065    *  @ingroup non_mutating_algorithms
4066    *  @param  __first  An input iterator.
4067    *  @param  __last   An input iterator.
4068    *  @param  __value  The value to be counted.
4069    *  @return   The number of iterators @c i in the range @p [__first,__last)
4070    *  for which @c *i == @p __value
4071   */
4072   template<typename _InputIterator, typename _Tp>
4073     inline typename iterator_traits<_InputIterator>::difference_type
4074     count(_InputIterator __first, _InputIterator __last, const _Tp& __value)
4075     {
4076       // concept requirements
4077       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4078       __glibcxx_function_requires(_EqualOpConcept<
4079 	    typename iterator_traits<_InputIterator>::value_type, _Tp>)
4080       __glibcxx_requires_valid_range(__first, __last);
4081 
4082       return std::__count_if(__first, __last,
4083 			     __gnu_cxx::__ops::__iter_equals_val(__value));
4084     }
4085 
4086   /**
4087    *  @brief Count the elements of a sequence for which a predicate is true.
4088    *  @ingroup non_mutating_algorithms
4089    *  @param  __first  An input iterator.
4090    *  @param  __last   An input iterator.
4091    *  @param  __pred   A predicate.
4092    *  @return   The number of iterators @c i in the range @p [__first,__last)
4093    *  for which @p __pred(*i) is true.
4094   */
4095   template<typename _InputIterator, typename _Predicate>
4096     inline typename iterator_traits<_InputIterator>::difference_type
4097     count_if(_InputIterator __first, _InputIterator __last, _Predicate __pred)
4098     {
4099       // concept requirements
4100       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4101       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4102 	    typename iterator_traits<_InputIterator>::value_type>)
4103       __glibcxx_requires_valid_range(__first, __last);
4104 
4105       return std::__count_if(__first, __last,
4106 			     __gnu_cxx::__ops::__pred_iter(__pred));
4107     }
4108 
4109   /**
4110    *  @brief Search a sequence for a matching sub-sequence.
4111    *  @ingroup non_mutating_algorithms
4112    *  @param  __first1  A forward iterator.
4113    *  @param  __last1   A forward iterator.
4114    *  @param  __first2  A forward iterator.
4115    *  @param  __last2   A forward iterator.
4116    *  @return The first iterator @c i in the range @p
4117    *  [__first1,__last1-(__last2-__first2)) such that @c *(i+N) == @p
4118    *  *(__first2+N) for each @c N in the range @p
4119    *  [0,__last2-__first2), or @p __last1 if no such iterator exists.
4120    *
4121    *  Searches the range @p [__first1,__last1) for a sub-sequence that
4122    *  compares equal value-by-value with the sequence given by @p
4123    *  [__first2,__last2) and returns an iterator to the first element
4124    *  of the sub-sequence, or @p __last1 if the sub-sequence is not
4125    *  found.
4126    *
4127    *  Because the sub-sequence must lie completely within the range @p
4128    *  [__first1,__last1) it must start at a position less than @p
4129    *  __last1-(__last2-__first2) where @p __last2-__first2 is the
4130    *  length of the sub-sequence.
4131    *
4132    *  This means that the returned iterator @c i will be in the range
4133    *  @p [__first1,__last1-(__last2-__first2))
4134   */
4135   template<typename _ForwardIterator1, typename _ForwardIterator2>
4136     inline _ForwardIterator1
4137     search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
4138 	   _ForwardIterator2 __first2, _ForwardIterator2 __last2)
4139     {
4140       // concept requirements
4141       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
4142       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
4143       __glibcxx_function_requires(_EqualOpConcept<
4144 	    typename iterator_traits<_ForwardIterator1>::value_type,
4145 	    typename iterator_traits<_ForwardIterator2>::value_type>)
4146       __glibcxx_requires_valid_range(__first1, __last1);
4147       __glibcxx_requires_valid_range(__first2, __last2);
4148 
4149       return std::__search(__first1, __last1, __first2, __last2,
4150 			   __gnu_cxx::__ops::__iter_equal_to_iter());
4151     }
4152 
4153   /**
4154    *  @brief Search a sequence for a matching sub-sequence using a predicate.
4155    *  @ingroup non_mutating_algorithms
4156    *  @param  __first1     A forward iterator.
4157    *  @param  __last1      A forward iterator.
4158    *  @param  __first2     A forward iterator.
4159    *  @param  __last2      A forward iterator.
4160    *  @param  __predicate  A binary predicate.
4161    *  @return   The first iterator @c i in the range
4162    *  @p [__first1,__last1-(__last2-__first2)) such that
4163    *  @p __predicate(*(i+N),*(__first2+N)) is true for each @c N in the range
4164    *  @p [0,__last2-__first2), or @p __last1 if no such iterator exists.
4165    *
4166    *  Searches the range @p [__first1,__last1) for a sub-sequence that
4167    *  compares equal value-by-value with the sequence given by @p
4168    *  [__first2,__last2), using @p __predicate to determine equality,
4169    *  and returns an iterator to the first element of the
4170    *  sub-sequence, or @p __last1 if no such iterator exists.
4171    *
4172    *  @see search(_ForwardIter1, _ForwardIter1, _ForwardIter2, _ForwardIter2)
4173   */
4174   template<typename _ForwardIterator1, typename _ForwardIterator2,
4175 	   typename _BinaryPredicate>
4176     inline _ForwardIterator1
4177     search(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
4178 	   _ForwardIterator2 __first2, _ForwardIterator2 __last2,
4179 	   _BinaryPredicate  __predicate)
4180     {
4181       // concept requirements
4182       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator1>)
4183       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator2>)
4184       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4185 	    typename iterator_traits<_ForwardIterator1>::value_type,
4186 	    typename iterator_traits<_ForwardIterator2>::value_type>)
4187       __glibcxx_requires_valid_range(__first1, __last1);
4188       __glibcxx_requires_valid_range(__first2, __last2);
4189 
4190       return std::__search(__first1, __last1, __first2, __last2,
4191 			   __gnu_cxx::__ops::__iter_comp_iter(__predicate));
4192     }
4193 
4194   /**
4195    *  @brief Search a sequence for a number of consecutive values.
4196    *  @ingroup non_mutating_algorithms
4197    *  @param  __first  A forward iterator.
4198    *  @param  __last   A forward iterator.
4199    *  @param  __count  The number of consecutive values.
4200    *  @param  __val    The value to find.
4201    *  @return The first iterator @c i in the range @p
4202    *  [__first,__last-__count) such that @c *(i+N) == @p __val for
4203    *  each @c N in the range @p [0,__count), or @p __last if no such
4204    *  iterator exists.
4205    *
4206    *  Searches the range @p [__first,__last) for @p count consecutive elements
4207    *  equal to @p __val.
4208   */
4209   template<typename _ForwardIterator, typename _Integer, typename _Tp>
4210     inline _ForwardIterator
4211     search_n(_ForwardIterator __first, _ForwardIterator __last,
4212 	     _Integer __count, const _Tp& __val)
4213     {
4214       // concept requirements
4215       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4216       __glibcxx_function_requires(_EqualOpConcept<
4217 	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4218       __glibcxx_requires_valid_range(__first, __last);
4219 
4220       return std::__search_n(__first, __last, __count,
4221 			     __gnu_cxx::__ops::__iter_equals_val(__val));
4222     }
4223 
4224 
4225   /**
4226    *  @brief Search a sequence for a number of consecutive values using a
4227    *         predicate.
4228    *  @ingroup non_mutating_algorithms
4229    *  @param  __first        A forward iterator.
4230    *  @param  __last         A forward iterator.
4231    *  @param  __count        The number of consecutive values.
4232    *  @param  __val          The value to find.
4233    *  @param  __binary_pred  A binary predicate.
4234    *  @return The first iterator @c i in the range @p
4235    *  [__first,__last-__count) such that @p
4236    *  __binary_pred(*(i+N),__val) is true for each @c N in the range
4237    *  @p [0,__count), or @p __last if no such iterator exists.
4238    *
4239    *  Searches the range @p [__first,__last) for @p __count
4240    *  consecutive elements for which the predicate returns true.
4241   */
4242   template<typename _ForwardIterator, typename _Integer, typename _Tp,
4243 	   typename _BinaryPredicate>
4244     inline _ForwardIterator
4245     search_n(_ForwardIterator __first, _ForwardIterator __last,
4246 	     _Integer __count, const _Tp& __val,
4247 	     _BinaryPredicate __binary_pred)
4248     {
4249       // concept requirements
4250       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4251       __glibcxx_function_requires(_BinaryPredicateConcept<_BinaryPredicate,
4252 	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4253       __glibcxx_requires_valid_range(__first, __last);
4254 
4255       return std::__search_n(__first, __last, __count,
4256 		__gnu_cxx::__ops::__iter_comp_val(__binary_pred, __val));
4257     }
4258 
4259 #if __cplusplus > 201402L
4260   /** @brief Search a sequence using a Searcher object.
4261    *
4262    *  @param  __first        A forward iterator.
4263    *  @param  __last         A forward iterator.
4264    *  @param  __searcher     A callable object.
4265    *  @return @p __searcher(__first,__last).first
4266   */
4267   template<typename _ForwardIterator, typename _Searcher>
4268     inline _ForwardIterator
4269     search(_ForwardIterator __first, _ForwardIterator __last,
4270 	   const _Searcher& __searcher)
4271     { return __searcher(__first, __last).first; }
4272 #endif
4273 
4274   /**
4275    *  @brief Perform an operation on a sequence.
4276    *  @ingroup mutating_algorithms
4277    *  @param  __first     An input iterator.
4278    *  @param  __last      An input iterator.
4279    *  @param  __result    An output iterator.
4280    *  @param  __unary_op  A unary operator.
4281    *  @return   An output iterator equal to @p __result+(__last-__first).
4282    *
4283    *  Applies the operator to each element in the input range and assigns
4284    *  the results to successive elements of the output sequence.
4285    *  Evaluates @p *(__result+N)=unary_op(*(__first+N)) for each @c N in the
4286    *  range @p [0,__last-__first).
4287    *
4288    *  @p unary_op must not alter its argument.
4289   */
4290   template<typename _InputIterator, typename _OutputIterator,
4291 	   typename _UnaryOperation>
4292     _OutputIterator
4293     transform(_InputIterator __first, _InputIterator __last,
4294 	      _OutputIterator __result, _UnaryOperation __unary_op)
4295     {
4296       // concept requirements
4297       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4298       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4299 	    // "the type returned by a _UnaryOperation"
4300 	    __typeof__(__unary_op(*__first))>)
4301       __glibcxx_requires_valid_range(__first, __last);
4302 
4303       for (; __first != __last; ++__first, (void)++__result)
4304 	*__result = __unary_op(*__first);
4305       return __result;
4306     }
4307 
4308   /**
4309    *  @brief Perform an operation on corresponding elements of two sequences.
4310    *  @ingroup mutating_algorithms
4311    *  @param  __first1     An input iterator.
4312    *  @param  __last1      An input iterator.
4313    *  @param  __first2     An input iterator.
4314    *  @param  __result     An output iterator.
4315    *  @param  __binary_op  A binary operator.
4316    *  @return   An output iterator equal to @p result+(last-first).
4317    *
4318    *  Applies the operator to the corresponding elements in the two
4319    *  input ranges and assigns the results to successive elements of the
4320    *  output sequence.
4321    *  Evaluates @p
4322    *  *(__result+N)=__binary_op(*(__first1+N),*(__first2+N)) for each
4323    *  @c N in the range @p [0,__last1-__first1).
4324    *
4325    *  @p binary_op must not alter either of its arguments.
4326   */
4327   template<typename _InputIterator1, typename _InputIterator2,
4328 	   typename _OutputIterator, typename _BinaryOperation>
4329     _OutputIterator
4330     transform(_InputIterator1 __first1, _InputIterator1 __last1,
4331 	      _InputIterator2 __first2, _OutputIterator __result,
4332 	      _BinaryOperation __binary_op)
4333     {
4334       // concept requirements
4335       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4336       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4337       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4338 	    // "the type returned by a _BinaryOperation"
4339 	    __typeof__(__binary_op(*__first1,*__first2))>)
4340       __glibcxx_requires_valid_range(__first1, __last1);
4341 
4342       for (; __first1 != __last1; ++__first1, (void)++__first2, ++__result)
4343 	*__result = __binary_op(*__first1, *__first2);
4344       return __result;
4345     }
4346 
4347   /**
4348    *  @brief Replace each occurrence of one value in a sequence with another
4349    *         value.
4350    *  @ingroup mutating_algorithms
4351    *  @param  __first      A forward iterator.
4352    *  @param  __last       A forward iterator.
4353    *  @param  __old_value  The value to be replaced.
4354    *  @param  __new_value  The replacement value.
4355    *  @return   replace() returns no value.
4356    *
4357    *  For each iterator @c i in the range @p [__first,__last) if @c *i ==
4358    *  @p __old_value then the assignment @c *i = @p __new_value is performed.
4359   */
4360   template<typename _ForwardIterator, typename _Tp>
4361     void
4362     replace(_ForwardIterator __first, _ForwardIterator __last,
4363 	    const _Tp& __old_value, const _Tp& __new_value)
4364     {
4365       // concept requirements
4366       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4367 				  _ForwardIterator>)
4368       __glibcxx_function_requires(_EqualOpConcept<
4369 	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
4370       __glibcxx_function_requires(_ConvertibleConcept<_Tp,
4371 	    typename iterator_traits<_ForwardIterator>::value_type>)
4372       __glibcxx_requires_valid_range(__first, __last);
4373 
4374       for (; __first != __last; ++__first)
4375 	if (*__first == __old_value)
4376 	  *__first = __new_value;
4377     }
4378 
4379   /**
4380    *  @brief Replace each value in a sequence for which a predicate returns
4381    *         true with another value.
4382    *  @ingroup mutating_algorithms
4383    *  @param  __first      A forward iterator.
4384    *  @param  __last       A forward iterator.
4385    *  @param  __pred       A predicate.
4386    *  @param  __new_value  The replacement value.
4387    *  @return   replace_if() returns no value.
4388    *
4389    *  For each iterator @c i in the range @p [__first,__last) if @p __pred(*i)
4390    *  is true then the assignment @c *i = @p __new_value is performed.
4391   */
4392   template<typename _ForwardIterator, typename _Predicate, typename _Tp>
4393     void
4394     replace_if(_ForwardIterator __first, _ForwardIterator __last,
4395 	       _Predicate __pred, const _Tp& __new_value)
4396     {
4397       // concept requirements
4398       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4399 				  _ForwardIterator>)
4400       __glibcxx_function_requires(_ConvertibleConcept<_Tp,
4401 	    typename iterator_traits<_ForwardIterator>::value_type>)
4402       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4403 	    typename iterator_traits<_ForwardIterator>::value_type>)
4404       __glibcxx_requires_valid_range(__first, __last);
4405 
4406       for (; __first != __last; ++__first)
4407 	if (__pred(*__first))
4408 	  *__first = __new_value;
4409     }
4410 
4411   /**
4412    *  @brief Assign the result of a function object to each value in a
4413    *         sequence.
4414    *  @ingroup mutating_algorithms
4415    *  @param  __first  A forward iterator.
4416    *  @param  __last   A forward iterator.
4417    *  @param  __gen    A function object taking no arguments and returning
4418    *                 std::iterator_traits<_ForwardIterator>::value_type
4419    *  @return   generate() returns no value.
4420    *
4421    *  Performs the assignment @c *i = @p __gen() for each @c i in the range
4422    *  @p [__first,__last).
4423   */
4424   template<typename _ForwardIterator, typename _Generator>
4425     void
4426     generate(_ForwardIterator __first, _ForwardIterator __last,
4427 	     _Generator __gen)
4428     {
4429       // concept requirements
4430       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
4431       __glibcxx_function_requires(_GeneratorConcept<_Generator,
4432 	    typename iterator_traits<_ForwardIterator>::value_type>)
4433       __glibcxx_requires_valid_range(__first, __last);
4434 
4435       for (; __first != __last; ++__first)
4436 	*__first = __gen();
4437     }
4438 
4439   /**
4440    *  @brief Assign the result of a function object to each value in a
4441    *         sequence.
4442    *  @ingroup mutating_algorithms
4443    *  @param  __first  A forward iterator.
4444    *  @param  __n      The length of the sequence.
4445    *  @param  __gen    A function object taking no arguments and returning
4446    *                 std::iterator_traits<_ForwardIterator>::value_type
4447    *  @return   The end of the sequence, @p __first+__n
4448    *
4449    *  Performs the assignment @c *i = @p __gen() for each @c i in the range
4450    *  @p [__first,__first+__n).
4451    *
4452    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
4453    *  DR 865. More algorithms that throw away information
4454   */
4455   template<typename _OutputIterator, typename _Size, typename _Generator>
4456     _OutputIterator
4457     generate_n(_OutputIterator __first, _Size __n, _Generator __gen)
4458     {
4459       // concept requirements
4460       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4461 	    // "the type returned by a _Generator"
4462 	    __typeof__(__gen())>)
4463 
4464       for (__decltype(__n + 0) __niter = __n;
4465 	   __niter > 0; --__niter, (void) ++__first)
4466 	*__first = __gen();
4467       return __first;
4468     }
4469 
4470   /**
4471    *  @brief Copy a sequence, removing consecutive duplicate values.
4472    *  @ingroup mutating_algorithms
4473    *  @param  __first   An input iterator.
4474    *  @param  __last    An input iterator.
4475    *  @param  __result  An output iterator.
4476    *  @return   An iterator designating the end of the resulting sequence.
4477    *
4478    *  Copies each element in the range @p [__first,__last) to the range
4479    *  beginning at @p __result, except that only the first element is copied
4480    *  from groups of consecutive elements that compare equal.
4481    *  unique_copy() is stable, so the relative order of elements that are
4482    *  copied is unchanged.
4483    *
4484    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
4485    *  DR 241. Does unique_copy() require CopyConstructible and Assignable?
4486    *
4487    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
4488    *  DR 538. 241 again: Does unique_copy() require CopyConstructible and
4489    *  Assignable?
4490   */
4491   template<typename _InputIterator, typename _OutputIterator>
4492     inline _OutputIterator
4493     unique_copy(_InputIterator __first, _InputIterator __last,
4494 		_OutputIterator __result)
4495     {
4496       // concept requirements
4497       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4498       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4499 	    typename iterator_traits<_InputIterator>::value_type>)
4500       __glibcxx_function_requires(_EqualityComparableConcept<
4501 	    typename iterator_traits<_InputIterator>::value_type>)
4502       __glibcxx_requires_valid_range(__first, __last);
4503 
4504       if (__first == __last)
4505 	return __result;
4506       return std::__unique_copy(__first, __last, __result,
4507 				__gnu_cxx::__ops::__iter_equal_to_iter(),
4508 				std::__iterator_category(__first),
4509 				std::__iterator_category(__result));
4510     }
4511 
4512   /**
4513    *  @brief Copy a sequence, removing consecutive values using a predicate.
4514    *  @ingroup mutating_algorithms
4515    *  @param  __first        An input iterator.
4516    *  @param  __last         An input iterator.
4517    *  @param  __result       An output iterator.
4518    *  @param  __binary_pred  A binary predicate.
4519    *  @return   An iterator designating the end of the resulting sequence.
4520    *
4521    *  Copies each element in the range @p [__first,__last) to the range
4522    *  beginning at @p __result, except that only the first element is copied
4523    *  from groups of consecutive elements for which @p __binary_pred returns
4524    *  true.
4525    *  unique_copy() is stable, so the relative order of elements that are
4526    *  copied is unchanged.
4527    *
4528    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
4529    *  DR 241. Does unique_copy() require CopyConstructible and Assignable?
4530   */
4531   template<typename _InputIterator, typename _OutputIterator,
4532 	   typename _BinaryPredicate>
4533     inline _OutputIterator
4534     unique_copy(_InputIterator __first, _InputIterator __last,
4535 		_OutputIterator __result,
4536 		_BinaryPredicate __binary_pred)
4537     {
4538       // concept requirements -- predicates checked later
4539       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator>)
4540       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4541 	    typename iterator_traits<_InputIterator>::value_type>)
4542       __glibcxx_requires_valid_range(__first, __last);
4543 
4544       if (__first == __last)
4545 	return __result;
4546       return std::__unique_copy(__first, __last, __result,
4547 			__gnu_cxx::__ops::__iter_comp_iter(__binary_pred),
4548 				std::__iterator_category(__first),
4549 				std::__iterator_category(__result));
4550     }
4551 
4552 #if _GLIBCXX_HOSTED
4553   /**
4554    *  @brief Randomly shuffle the elements of a sequence.
4555    *  @ingroup mutating_algorithms
4556    *  @param  __first   A forward iterator.
4557    *  @param  __last    A forward iterator.
4558    *  @return  Nothing.
4559    *
4560    *  Reorder the elements in the range @p [__first,__last) using a random
4561    *  distribution, so that every possible ordering of the sequence is
4562    *  equally likely.
4563   */
4564   template<typename _RandomAccessIterator>
4565     inline void
4566     random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last)
4567     {
4568       // concept requirements
4569       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4570 	    _RandomAccessIterator>)
4571       __glibcxx_requires_valid_range(__first, __last);
4572 
4573       if (__first != __last)
4574 	for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
4575 	  {
4576 	    // XXX rand() % N is not uniformly distributed
4577 	    _RandomAccessIterator __j = __first
4578 					+ std::rand() % ((__i - __first) + 1);
4579 	    if (__i != __j)
4580 	      std::iter_swap(__i, __j);
4581 	  }
4582     }
4583 #endif
4584 
4585   /**
4586    *  @brief Shuffle the elements of a sequence using a random number
4587    *         generator.
4588    *  @ingroup mutating_algorithms
4589    *  @param  __first   A forward iterator.
4590    *  @param  __last    A forward iterator.
4591    *  @param  __rand    The RNG functor or function.
4592    *  @return  Nothing.
4593    *
4594    *  Reorders the elements in the range @p [__first,__last) using @p __rand to
4595    *  provide a random distribution. Calling @p __rand(N) for a positive
4596    *  integer @p N should return a randomly chosen integer from the
4597    *  range [0,N).
4598   */
4599   template<typename _RandomAccessIterator, typename _RandomNumberGenerator>
4600     void
4601     random_shuffle(_RandomAccessIterator __first, _RandomAccessIterator __last,
4602 #if __cplusplus >= 201103L
4603 		   _RandomNumberGenerator&& __rand)
4604 #else
4605 		   _RandomNumberGenerator& __rand)
4606 #endif
4607     {
4608       // concept requirements
4609       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4610 	    _RandomAccessIterator>)
4611       __glibcxx_requires_valid_range(__first, __last);
4612 
4613       if (__first == __last)
4614 	return;
4615       for (_RandomAccessIterator __i = __first + 1; __i != __last; ++__i)
4616 	{
4617 	  _RandomAccessIterator __j = __first + __rand((__i - __first) + 1);
4618 	  if (__i != __j)
4619 	    std::iter_swap(__i, __j);
4620 	}
4621     }
4622 
4623 
4624   /**
4625    *  @brief Move elements for which a predicate is true to the beginning
4626    *         of a sequence.
4627    *  @ingroup mutating_algorithms
4628    *  @param  __first   A forward iterator.
4629    *  @param  __last    A forward iterator.
4630    *  @param  __pred    A predicate functor.
4631    *  @return  An iterator @p middle such that @p __pred(i) is true for each
4632    *  iterator @p i in the range @p [__first,middle) and false for each @p i
4633    *  in the range @p [middle,__last).
4634    *
4635    *  @p __pred must not modify its operand. @p partition() does not preserve
4636    *  the relative ordering of elements in each group, use
4637    *  @p stable_partition() if this is needed.
4638   */
4639   template<typename _ForwardIterator, typename _Predicate>
4640     inline _ForwardIterator
4641     partition(_ForwardIterator __first, _ForwardIterator __last,
4642 	      _Predicate   __pred)
4643     {
4644       // concept requirements
4645       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
4646 				  _ForwardIterator>)
4647       __glibcxx_function_requires(_UnaryPredicateConcept<_Predicate,
4648 	    typename iterator_traits<_ForwardIterator>::value_type>)
4649       __glibcxx_requires_valid_range(__first, __last);
4650 
4651       return std::__partition(__first, __last, __pred,
4652 			      std::__iterator_category(__first));
4653     }
4654 
4655 
4656   /**
4657    *  @brief Sort the smallest elements of a sequence.
4658    *  @ingroup sorting_algorithms
4659    *  @param  __first   An iterator.
4660    *  @param  __middle  Another iterator.
4661    *  @param  __last    Another iterator.
4662    *  @return  Nothing.
4663    *
4664    *  Sorts the smallest @p (__middle-__first) elements in the range
4665    *  @p [first,last) and moves them to the range @p [__first,__middle). The
4666    *  order of the remaining elements in the range @p [__middle,__last) is
4667    *  undefined.
4668    *  After the sort if @e i and @e j are iterators in the range
4669    *  @p [__first,__middle) such that i precedes j and @e k is an iterator in
4670    *  the range @p [__middle,__last) then *j<*i and *k<*i are both false.
4671   */
4672   template<typename _RandomAccessIterator>
4673     inline void
4674     partial_sort(_RandomAccessIterator __first,
4675 		 _RandomAccessIterator __middle,
4676 		 _RandomAccessIterator __last)
4677     {
4678       // concept requirements
4679       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4680 	    _RandomAccessIterator>)
4681       __glibcxx_function_requires(_LessThanComparableConcept<
4682 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4683       __glibcxx_requires_valid_range(__first, __middle);
4684       __glibcxx_requires_valid_range(__middle, __last);
4685       __glibcxx_requires_irreflexive(__first, __last);
4686 
4687       std::__partial_sort(__first, __middle, __last,
4688 			  __gnu_cxx::__ops::__iter_less_iter());
4689     }
4690 
4691   /**
4692    *  @brief Sort the smallest elements of a sequence using a predicate
4693    *         for comparison.
4694    *  @ingroup sorting_algorithms
4695    *  @param  __first   An iterator.
4696    *  @param  __middle  Another iterator.
4697    *  @param  __last    Another iterator.
4698    *  @param  __comp    A comparison functor.
4699    *  @return  Nothing.
4700    *
4701    *  Sorts the smallest @p (__middle-__first) elements in the range
4702    *  @p [__first,__last) and moves them to the range @p [__first,__middle). The
4703    *  order of the remaining elements in the range @p [__middle,__last) is
4704    *  undefined.
4705    *  After the sort if @e i and @e j are iterators in the range
4706    *  @p [__first,__middle) such that i precedes j and @e k is an iterator in
4707    *  the range @p [__middle,__last) then @p *__comp(j,*i) and @p __comp(*k,*i)
4708    *  are both false.
4709   */
4710   template<typename _RandomAccessIterator, typename _Compare>
4711     inline void
4712     partial_sort(_RandomAccessIterator __first,
4713 		 _RandomAccessIterator __middle,
4714 		 _RandomAccessIterator __last,
4715 		 _Compare __comp)
4716     {
4717       // concept requirements
4718       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4719 	    _RandomAccessIterator>)
4720       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4721 	    typename iterator_traits<_RandomAccessIterator>::value_type,
4722 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4723       __glibcxx_requires_valid_range(__first, __middle);
4724       __glibcxx_requires_valid_range(__middle, __last);
4725       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4726 
4727       std::__partial_sort(__first, __middle, __last,
4728 			  __gnu_cxx::__ops::__iter_comp_iter(__comp));
4729     }
4730 
4731   /**
4732    *  @brief Sort a sequence just enough to find a particular position.
4733    *  @ingroup sorting_algorithms
4734    *  @param  __first   An iterator.
4735    *  @param  __nth     Another iterator.
4736    *  @param  __last    Another iterator.
4737    *  @return  Nothing.
4738    *
4739    *  Rearranges the elements in the range @p [__first,__last) so that @p *__nth
4740    *  is the same element that would have been in that position had the
4741    *  whole sequence been sorted. The elements either side of @p *__nth are
4742    *  not completely sorted, but for any iterator @e i in the range
4743    *  @p [__first,__nth) and any iterator @e j in the range @p [__nth,__last) it
4744    *  holds that *j < *i is false.
4745   */
4746   template<typename _RandomAccessIterator>
4747     inline void
4748     nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
4749 		_RandomAccessIterator __last)
4750     {
4751       // concept requirements
4752       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4753 				  _RandomAccessIterator>)
4754       __glibcxx_function_requires(_LessThanComparableConcept<
4755 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4756       __glibcxx_requires_valid_range(__first, __nth);
4757       __glibcxx_requires_valid_range(__nth, __last);
4758       __glibcxx_requires_irreflexive(__first, __last);
4759 
4760       if (__first == __last || __nth == __last)
4761 	return;
4762 
4763       std::__introselect(__first, __nth, __last,
4764 			 std::__lg(__last - __first) * 2,
4765 			 __gnu_cxx::__ops::__iter_less_iter());
4766     }
4767 
4768   /**
4769    *  @brief Sort a sequence just enough to find a particular position
4770    *         using a predicate for comparison.
4771    *  @ingroup sorting_algorithms
4772    *  @param  __first   An iterator.
4773    *  @param  __nth     Another iterator.
4774    *  @param  __last    Another iterator.
4775    *  @param  __comp    A comparison functor.
4776    *  @return  Nothing.
4777    *
4778    *  Rearranges the elements in the range @p [__first,__last) so that @p *__nth
4779    *  is the same element that would have been in that position had the
4780    *  whole sequence been sorted. The elements either side of @p *__nth are
4781    *  not completely sorted, but for any iterator @e i in the range
4782    *  @p [__first,__nth) and any iterator @e j in the range @p [__nth,__last) it
4783    *  holds that @p __comp(*j,*i) is false.
4784   */
4785   template<typename _RandomAccessIterator, typename _Compare>
4786     inline void
4787     nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
4788 		_RandomAccessIterator __last, _Compare __comp)
4789     {
4790       // concept requirements
4791       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4792 				  _RandomAccessIterator>)
4793       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4794 	    typename iterator_traits<_RandomAccessIterator>::value_type,
4795 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4796       __glibcxx_requires_valid_range(__first, __nth);
4797       __glibcxx_requires_valid_range(__nth, __last);
4798       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4799 
4800       if (__first == __last || __nth == __last)
4801 	return;
4802 
4803       std::__introselect(__first, __nth, __last,
4804 			 std::__lg(__last - __first) * 2,
4805 			 __gnu_cxx::__ops::__iter_comp_iter(__comp));
4806     }
4807 
4808   /**
4809    *  @brief Sort the elements of a sequence.
4810    *  @ingroup sorting_algorithms
4811    *  @param  __first   An iterator.
4812    *  @param  __last    Another iterator.
4813    *  @return  Nothing.
4814    *
4815    *  Sorts the elements in the range @p [__first,__last) in ascending order,
4816    *  such that for each iterator @e i in the range @p [__first,__last-1),
4817    *  *(i+1)<*i is false.
4818    *
4819    *  The relative ordering of equivalent elements is not preserved, use
4820    *  @p stable_sort() if this is needed.
4821   */
4822   template<typename _RandomAccessIterator>
4823     inline void
4824     sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
4825     {
4826       // concept requirements
4827       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4828 	    _RandomAccessIterator>)
4829       __glibcxx_function_requires(_LessThanComparableConcept<
4830 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4831       __glibcxx_requires_valid_range(__first, __last);
4832       __glibcxx_requires_irreflexive(__first, __last);
4833 
4834       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_less_iter());
4835     }
4836 
4837   /**
4838    *  @brief Sort the elements of a sequence using a predicate for comparison.
4839    *  @ingroup sorting_algorithms
4840    *  @param  __first   An iterator.
4841    *  @param  __last    Another iterator.
4842    *  @param  __comp    A comparison functor.
4843    *  @return  Nothing.
4844    *
4845    *  Sorts the elements in the range @p [__first,__last) in ascending order,
4846    *  such that @p __comp(*(i+1),*i) is false for every iterator @e i in the
4847    *  range @p [__first,__last-1).
4848    *
4849    *  The relative ordering of equivalent elements is not preserved, use
4850    *  @p stable_sort() if this is needed.
4851   */
4852   template<typename _RandomAccessIterator, typename _Compare>
4853     inline void
4854     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
4855 	 _Compare __comp)
4856     {
4857       // concept requirements
4858       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
4859 	    _RandomAccessIterator>)
4860       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4861 	    typename iterator_traits<_RandomAccessIterator>::value_type,
4862 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
4863       __glibcxx_requires_valid_range(__first, __last);
4864       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
4865 
4866       std::__sort(__first, __last, __gnu_cxx::__ops::__iter_comp_iter(__comp));
4867     }
4868 
4869   template<typename _InputIterator1, typename _InputIterator2,
4870 	   typename _OutputIterator, typename _Compare>
4871     _OutputIterator
4872     __merge(_InputIterator1 __first1, _InputIterator1 __last1,
4873 	    _InputIterator2 __first2, _InputIterator2 __last2,
4874 	    _OutputIterator __result, _Compare __comp)
4875     {
4876       while (__first1 != __last1 && __first2 != __last2)
4877 	{
4878 	  if (__comp(__first2, __first1))
4879 	    {
4880 	      *__result = *__first2;
4881 	      ++__first2;
4882 	    }
4883 	  else
4884 	    {
4885 	      *__result = *__first1;
4886 	      ++__first1;
4887 	    }
4888 	  ++__result;
4889 	}
4890       return std::copy(__first2, __last2,
4891 		       std::copy(__first1, __last1, __result));
4892     }
4893 
4894   /**
4895    *  @brief Merges two sorted ranges.
4896    *  @ingroup sorting_algorithms
4897    *  @param  __first1  An iterator.
4898    *  @param  __first2  Another iterator.
4899    *  @param  __last1   Another iterator.
4900    *  @param  __last2   Another iterator.
4901    *  @param  __result  An iterator pointing to the end of the merged range.
4902    *  @return         An iterator pointing to the first element <em>not less
4903    *                  than</em> @e val.
4904    *
4905    *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
4906    *  the sorted range @p [__result, __result + (__last1-__first1) +
4907    *  (__last2-__first2)).  Both input ranges must be sorted, and the
4908    *  output range must not overlap with either of the input ranges.
4909    *  The sort is @e stable, that is, for equivalent elements in the
4910    *  two ranges, elements from the first range will always come
4911    *  before elements from the second.
4912   */
4913   template<typename _InputIterator1, typename _InputIterator2,
4914 	   typename _OutputIterator>
4915     inline _OutputIterator
4916     merge(_InputIterator1 __first1, _InputIterator1 __last1,
4917 	  _InputIterator2 __first2, _InputIterator2 __last2,
4918 	  _OutputIterator __result)
4919     {
4920       // concept requirements
4921       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4922       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4923       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4924 	    typename iterator_traits<_InputIterator1>::value_type>)
4925       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4926 	    typename iterator_traits<_InputIterator2>::value_type>)
4927       __glibcxx_function_requires(_LessThanOpConcept<
4928 	    typename iterator_traits<_InputIterator2>::value_type,
4929 	    typename iterator_traits<_InputIterator1>::value_type>)
4930       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
4931       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
4932       __glibcxx_requires_irreflexive2(__first1, __last1);
4933       __glibcxx_requires_irreflexive2(__first2, __last2);
4934 
4935       return _GLIBCXX_STD_A::__merge(__first1, __last1,
4936 				     __first2, __last2, __result,
4937 				     __gnu_cxx::__ops::__iter_less_iter());
4938     }
4939 
4940   /**
4941    *  @brief Merges two sorted ranges.
4942    *  @ingroup sorting_algorithms
4943    *  @param  __first1  An iterator.
4944    *  @param  __first2  Another iterator.
4945    *  @param  __last1   Another iterator.
4946    *  @param  __last2   Another iterator.
4947    *  @param  __result  An iterator pointing to the end of the merged range.
4948    *  @param  __comp    A functor to use for comparisons.
4949    *  @return         An iterator pointing to the first element "not less
4950    *                  than" @e val.
4951    *
4952    *  Merges the ranges @p [__first1,__last1) and @p [__first2,__last2) into
4953    *  the sorted range @p [__result, __result + (__last1-__first1) +
4954    *  (__last2-__first2)).  Both input ranges must be sorted, and the
4955    *  output range must not overlap with either of the input ranges.
4956    *  The sort is @e stable, that is, for equivalent elements in the
4957    *  two ranges, elements from the first range will always come
4958    *  before elements from the second.
4959    *
4960    *  The comparison function should have the same effects on ordering as
4961    *  the function used for the initial sort.
4962   */
4963   template<typename _InputIterator1, typename _InputIterator2,
4964 	   typename _OutputIterator, typename _Compare>
4965     inline _OutputIterator
4966     merge(_InputIterator1 __first1, _InputIterator1 __last1,
4967 	  _InputIterator2 __first2, _InputIterator2 __last2,
4968 	  _OutputIterator __result, _Compare __comp)
4969     {
4970       // concept requirements
4971       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
4972       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
4973       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4974 	    typename iterator_traits<_InputIterator1>::value_type>)
4975       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
4976 	    typename iterator_traits<_InputIterator2>::value_type>)
4977       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
4978 	    typename iterator_traits<_InputIterator2>::value_type,
4979 	    typename iterator_traits<_InputIterator1>::value_type>)
4980       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
4981       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
4982       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
4983       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
4984 
4985       return _GLIBCXX_STD_A::__merge(__first1, __last1,
4986 				__first2, __last2, __result,
4987 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
4988     }
4989 
4990   template<typename _RandomAccessIterator, typename _Compare>
4991     inline void
4992     __stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
4993 		  _Compare __comp)
4994     {
4995       typedef typename iterator_traits<_RandomAccessIterator>::value_type
4996 	_ValueType;
4997       typedef typename iterator_traits<_RandomAccessIterator>::difference_type
4998 	_DistanceType;
4999 
5000       typedef _Temporary_buffer<_RandomAccessIterator, _ValueType> _TmpBuf;
5001       _TmpBuf __buf(__first, __last);
5002 
5003       if (__buf.begin() == 0)
5004 	std::__inplace_stable_sort(__first, __last, __comp);
5005       else
5006 	std::__stable_sort_adaptive(__first, __last, __buf.begin(),
5007 				    _DistanceType(__buf.size()), __comp);
5008     }
5009 
5010   /**
5011    *  @brief Sort the elements of a sequence, preserving the relative order
5012    *         of equivalent elements.
5013    *  @ingroup sorting_algorithms
5014    *  @param  __first   An iterator.
5015    *  @param  __last    Another iterator.
5016    *  @return  Nothing.
5017    *
5018    *  Sorts the elements in the range @p [__first,__last) in ascending order,
5019    *  such that for each iterator @p i in the range @p [__first,__last-1),
5020    *  @p *(i+1)<*i is false.
5021    *
5022    *  The relative ordering of equivalent elements is preserved, so any two
5023    *  elements @p x and @p y in the range @p [__first,__last) such that
5024    *  @p x<y is false and @p y<x is false will have the same relative
5025    *  ordering after calling @p stable_sort().
5026   */
5027   template<typename _RandomAccessIterator>
5028     inline void
5029     stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
5030     {
5031       // concept requirements
5032       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
5033 	    _RandomAccessIterator>)
5034       __glibcxx_function_requires(_LessThanComparableConcept<
5035 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
5036       __glibcxx_requires_valid_range(__first, __last);
5037       __glibcxx_requires_irreflexive(__first, __last);
5038 
5039       _GLIBCXX_STD_A::__stable_sort(__first, __last,
5040 				    __gnu_cxx::__ops::__iter_less_iter());
5041     }
5042 
5043   /**
5044    *  @brief Sort the elements of a sequence using a predicate for comparison,
5045    *         preserving the relative order of equivalent elements.
5046    *  @ingroup sorting_algorithms
5047    *  @param  __first   An iterator.
5048    *  @param  __last    Another iterator.
5049    *  @param  __comp    A comparison functor.
5050    *  @return  Nothing.
5051    *
5052    *  Sorts the elements in the range @p [__first,__last) in ascending order,
5053    *  such that for each iterator @p i in the range @p [__first,__last-1),
5054    *  @p __comp(*(i+1),*i) is false.
5055    *
5056    *  The relative ordering of equivalent elements is preserved, so any two
5057    *  elements @p x and @p y in the range @p [__first,__last) such that
5058    *  @p __comp(x,y) is false and @p __comp(y,x) is false will have the same
5059    *  relative ordering after calling @p stable_sort().
5060   */
5061   template<typename _RandomAccessIterator, typename _Compare>
5062     inline void
5063     stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
5064 		_Compare __comp)
5065     {
5066       // concept requirements
5067       __glibcxx_function_requires(_Mutable_RandomAccessIteratorConcept<
5068 	    _RandomAccessIterator>)
5069       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5070 	    typename iterator_traits<_RandomAccessIterator>::value_type,
5071 	    typename iterator_traits<_RandomAccessIterator>::value_type>)
5072       __glibcxx_requires_valid_range(__first, __last);
5073       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5074 
5075       _GLIBCXX_STD_A::__stable_sort(__first, __last,
5076 				    __gnu_cxx::__ops::__iter_comp_iter(__comp));
5077     }
5078 
5079   template<typename _InputIterator1, typename _InputIterator2,
5080 	   typename _OutputIterator,
5081 	   typename _Compare>
5082     _OutputIterator
5083     __set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5084 		_InputIterator2 __first2, _InputIterator2 __last2,
5085 		_OutputIterator __result, _Compare __comp)
5086     {
5087       while (__first1 != __last1 && __first2 != __last2)
5088 	{
5089 	  if (__comp(__first1, __first2))
5090 	    {
5091 	      *__result = *__first1;
5092 	      ++__first1;
5093 	    }
5094 	  else if (__comp(__first2, __first1))
5095 	    {
5096 	      *__result = *__first2;
5097 	      ++__first2;
5098 	    }
5099 	  else
5100 	    {
5101 	      *__result = *__first1;
5102 	      ++__first1;
5103 	      ++__first2;
5104 	    }
5105 	  ++__result;
5106 	}
5107       return std::copy(__first2, __last2,
5108 		       std::copy(__first1, __last1, __result));
5109     }
5110 
5111   /**
5112    *  @brief Return the union of two sorted ranges.
5113    *  @ingroup set_algorithms
5114    *  @param  __first1  Start of first range.
5115    *  @param  __last1   End of first range.
5116    *  @param  __first2  Start of second range.
5117    *  @param  __last2   End of second range.
5118    *  @param  __result  Start of output range.
5119    *  @return  End of the output range.
5120    *  @ingroup set_algorithms
5121    *
5122    *  This operation iterates over both ranges, copying elements present in
5123    *  each range in order to the output range.  Iterators increment for each
5124    *  range.  When the current element of one range is less than the other,
5125    *  that element is copied and the iterator advanced.  If an element is
5126    *  contained in both ranges, the element from the first range is copied and
5127    *  both ranges advance.  The output range may not overlap either input
5128    *  range.
5129   */
5130   template<typename _InputIterator1, typename _InputIterator2,
5131 	   typename _OutputIterator>
5132     inline _OutputIterator
5133     set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5134 	      _InputIterator2 __first2, _InputIterator2 __last2,
5135 	      _OutputIterator __result)
5136     {
5137       // concept requirements
5138       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5139       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5140       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5141 	    typename iterator_traits<_InputIterator1>::value_type>)
5142       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5143 	    typename iterator_traits<_InputIterator2>::value_type>)
5144       __glibcxx_function_requires(_LessThanOpConcept<
5145 	    typename iterator_traits<_InputIterator1>::value_type,
5146 	    typename iterator_traits<_InputIterator2>::value_type>)
5147       __glibcxx_function_requires(_LessThanOpConcept<
5148 	    typename iterator_traits<_InputIterator2>::value_type,
5149 	    typename iterator_traits<_InputIterator1>::value_type>)
5150       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
5151       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
5152       __glibcxx_requires_irreflexive2(__first1, __last1);
5153       __glibcxx_requires_irreflexive2(__first2, __last2);
5154 
5155       return _GLIBCXX_STD_A::__set_union(__first1, __last1,
5156 				__first2, __last2, __result,
5157 				__gnu_cxx::__ops::__iter_less_iter());
5158     }
5159 
5160   /**
5161    *  @brief Return the union of two sorted ranges using a comparison functor.
5162    *  @ingroup set_algorithms
5163    *  @param  __first1  Start of first range.
5164    *  @param  __last1   End of first range.
5165    *  @param  __first2  Start of second range.
5166    *  @param  __last2   End of second range.
5167    *  @param  __result  Start of output range.
5168    *  @param  __comp    The comparison functor.
5169    *  @return  End of the output range.
5170    *  @ingroup set_algorithms
5171    *
5172    *  This operation iterates over both ranges, copying elements present in
5173    *  each range in order to the output range.  Iterators increment for each
5174    *  range.  When the current element of one range is less than the other
5175    *  according to @p __comp, that element is copied and the iterator advanced.
5176    *  If an equivalent element according to @p __comp is contained in both
5177    *  ranges, the element from the first range is copied and both ranges
5178    *  advance.  The output range may not overlap either input range.
5179   */
5180   template<typename _InputIterator1, typename _InputIterator2,
5181 	   typename _OutputIterator, typename _Compare>
5182     inline _OutputIterator
5183     set_union(_InputIterator1 __first1, _InputIterator1 __last1,
5184 	      _InputIterator2 __first2, _InputIterator2 __last2,
5185 	      _OutputIterator __result, _Compare __comp)
5186     {
5187       // concept requirements
5188       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5189       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5190       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5191 	    typename iterator_traits<_InputIterator1>::value_type>)
5192       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5193 	    typename iterator_traits<_InputIterator2>::value_type>)
5194       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5195 	    typename iterator_traits<_InputIterator1>::value_type,
5196 	    typename iterator_traits<_InputIterator2>::value_type>)
5197       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5198 	    typename iterator_traits<_InputIterator2>::value_type,
5199 	    typename iterator_traits<_InputIterator1>::value_type>)
5200       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5201       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5202       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5203       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5204 
5205       return _GLIBCXX_STD_A::__set_union(__first1, __last1,
5206 				__first2, __last2, __result,
5207 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
5208     }
5209 
5210   template<typename _InputIterator1, typename _InputIterator2,
5211 	   typename _OutputIterator,
5212 	   typename _Compare>
5213     _OutputIterator
5214     __set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5215 		       _InputIterator2 __first2, _InputIterator2 __last2,
5216 		       _OutputIterator __result, _Compare __comp)
5217     {
5218       while (__first1 != __last1 && __first2 != __last2)
5219 	if (__comp(__first1, __first2))
5220 	  ++__first1;
5221 	else if (__comp(__first2, __first1))
5222 	  ++__first2;
5223 	else
5224 	  {
5225 	    *__result = *__first1;
5226 	    ++__first1;
5227 	    ++__first2;
5228 	    ++__result;
5229 	  }
5230       return __result;
5231     }
5232 
5233   /**
5234    *  @brief Return the intersection of two sorted ranges.
5235    *  @ingroup set_algorithms
5236    *  @param  __first1  Start of first range.
5237    *  @param  __last1   End of first range.
5238    *  @param  __first2  Start of second range.
5239    *  @param  __last2   End of second range.
5240    *  @param  __result  Start of output range.
5241    *  @return  End of the output range.
5242    *  @ingroup set_algorithms
5243    *
5244    *  This operation iterates over both ranges, copying elements present in
5245    *  both ranges in order to the output range.  Iterators increment for each
5246    *  range.  When the current element of one range is less than the other,
5247    *  that iterator advances.  If an element is contained in both ranges, the
5248    *  element from the first range is copied and both ranges advance.  The
5249    *  output range may not overlap either input range.
5250   */
5251   template<typename _InputIterator1, typename _InputIterator2,
5252 	   typename _OutputIterator>
5253     inline _OutputIterator
5254     set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5255 		     _InputIterator2 __first2, _InputIterator2 __last2,
5256 		     _OutputIterator __result)
5257     {
5258       // concept requirements
5259       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5260       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5261       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5262 	    typename iterator_traits<_InputIterator1>::value_type>)
5263       __glibcxx_function_requires(_LessThanOpConcept<
5264 	    typename iterator_traits<_InputIterator1>::value_type,
5265 	    typename iterator_traits<_InputIterator2>::value_type>)
5266       __glibcxx_function_requires(_LessThanOpConcept<
5267 	    typename iterator_traits<_InputIterator2>::value_type,
5268 	    typename iterator_traits<_InputIterator1>::value_type>)
5269       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
5270       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
5271       __glibcxx_requires_irreflexive2(__first1, __last1);
5272       __glibcxx_requires_irreflexive2(__first2, __last2);
5273 
5274       return _GLIBCXX_STD_A::__set_intersection(__first1, __last1,
5275 				     __first2, __last2, __result,
5276 				     __gnu_cxx::__ops::__iter_less_iter());
5277     }
5278 
5279   /**
5280    *  @brief Return the intersection of two sorted ranges using comparison
5281    *  functor.
5282    *  @ingroup set_algorithms
5283    *  @param  __first1  Start of first range.
5284    *  @param  __last1   End of first range.
5285    *  @param  __first2  Start of second range.
5286    *  @param  __last2   End of second range.
5287    *  @param  __result  Start of output range.
5288    *  @param  __comp    The comparison functor.
5289    *  @return  End of the output range.
5290    *  @ingroup set_algorithms
5291    *
5292    *  This operation iterates over both ranges, copying elements present in
5293    *  both ranges in order to the output range.  Iterators increment for each
5294    *  range.  When the current element of one range is less than the other
5295    *  according to @p __comp, that iterator advances.  If an element is
5296    *  contained in both ranges according to @p __comp, the element from the
5297    *  first range is copied and both ranges advance.  The output range may not
5298    *  overlap either input range.
5299   */
5300   template<typename _InputIterator1, typename _InputIterator2,
5301 	   typename _OutputIterator, typename _Compare>
5302     inline _OutputIterator
5303     set_intersection(_InputIterator1 __first1, _InputIterator1 __last1,
5304 		     _InputIterator2 __first2, _InputIterator2 __last2,
5305 		     _OutputIterator __result, _Compare __comp)
5306     {
5307       // concept requirements
5308       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5309       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5310       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5311 	    typename iterator_traits<_InputIterator1>::value_type>)
5312       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5313 	    typename iterator_traits<_InputIterator1>::value_type,
5314 	    typename iterator_traits<_InputIterator2>::value_type>)
5315       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5316 	    typename iterator_traits<_InputIterator2>::value_type,
5317 	    typename iterator_traits<_InputIterator1>::value_type>)
5318       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5319       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5320       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5321       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5322 
5323       return _GLIBCXX_STD_A::__set_intersection(__first1, __last1,
5324 				__first2, __last2, __result,
5325 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
5326     }
5327 
5328   template<typename _InputIterator1, typename _InputIterator2,
5329 	   typename _OutputIterator,
5330 	   typename _Compare>
5331     _OutputIterator
5332     __set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5333 		     _InputIterator2 __first2, _InputIterator2 __last2,
5334 		     _OutputIterator __result, _Compare __comp)
5335     {
5336       while (__first1 != __last1 && __first2 != __last2)
5337 	if (__comp(__first1, __first2))
5338 	  {
5339 	    *__result = *__first1;
5340 	    ++__first1;
5341 	    ++__result;
5342 	  }
5343 	else if (__comp(__first2, __first1))
5344 	  ++__first2;
5345 	else
5346 	  {
5347 	    ++__first1;
5348 	    ++__first2;
5349 	  }
5350       return std::copy(__first1, __last1, __result);
5351     }
5352 
5353   /**
5354    *  @brief Return the difference of two sorted ranges.
5355    *  @ingroup set_algorithms
5356    *  @param  __first1  Start of first range.
5357    *  @param  __last1   End of first range.
5358    *  @param  __first2  Start of second range.
5359    *  @param  __last2   End of second range.
5360    *  @param  __result  Start of output range.
5361    *  @return  End of the output range.
5362    *  @ingroup set_algorithms
5363    *
5364    *  This operation iterates over both ranges, copying elements present in
5365    *  the first range but not the second in order to the output range.
5366    *  Iterators increment for each range.  When the current element of the
5367    *  first range is less than the second, that element is copied and the
5368    *  iterator advances.  If the current element of the second range is less,
5369    *  the iterator advances, but no element is copied.  If an element is
5370    *  contained in both ranges, no elements are copied and both ranges
5371    *  advance.  The output range may not overlap either input range.
5372   */
5373   template<typename _InputIterator1, typename _InputIterator2,
5374 	   typename _OutputIterator>
5375     inline _OutputIterator
5376     set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5377 		   _InputIterator2 __first2, _InputIterator2 __last2,
5378 		   _OutputIterator __result)
5379     {
5380       // concept requirements
5381       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5382       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5383       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5384 	    typename iterator_traits<_InputIterator1>::value_type>)
5385       __glibcxx_function_requires(_LessThanOpConcept<
5386 	    typename iterator_traits<_InputIterator1>::value_type,
5387 	    typename iterator_traits<_InputIterator2>::value_type>)
5388       __glibcxx_function_requires(_LessThanOpConcept<
5389 	    typename iterator_traits<_InputIterator2>::value_type,
5390 	    typename iterator_traits<_InputIterator1>::value_type>)
5391       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
5392       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
5393       __glibcxx_requires_irreflexive2(__first1, __last1);
5394       __glibcxx_requires_irreflexive2(__first2, __last2);
5395 
5396       return _GLIBCXX_STD_A::__set_difference(__first1, __last1,
5397 				   __first2, __last2, __result,
5398 				   __gnu_cxx::__ops::__iter_less_iter());
5399     }
5400 
5401   /**
5402    *  @brief  Return the difference of two sorted ranges using comparison
5403    *  functor.
5404    *  @ingroup set_algorithms
5405    *  @param  __first1  Start of first range.
5406    *  @param  __last1   End of first range.
5407    *  @param  __first2  Start of second range.
5408    *  @param  __last2   End of second range.
5409    *  @param  __result  Start of output range.
5410    *  @param  __comp    The comparison functor.
5411    *  @return  End of the output range.
5412    *  @ingroup set_algorithms
5413    *
5414    *  This operation iterates over both ranges, copying elements present in
5415    *  the first range but not the second in order to the output range.
5416    *  Iterators increment for each range.  When the current element of the
5417    *  first range is less than the second according to @p __comp, that element
5418    *  is copied and the iterator advances.  If the current element of the
5419    *  second range is less, no element is copied and the iterator advances.
5420    *  If an element is contained in both ranges according to @p __comp, no
5421    *  elements are copied and both ranges advance.  The output range may not
5422    *  overlap either input range.
5423   */
5424   template<typename _InputIterator1, typename _InputIterator2,
5425 	   typename _OutputIterator, typename _Compare>
5426     inline _OutputIterator
5427     set_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5428 		   _InputIterator2 __first2, _InputIterator2 __last2,
5429 		   _OutputIterator __result, _Compare __comp)
5430     {
5431       // concept requirements
5432       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5433       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5434       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5435 	    typename iterator_traits<_InputIterator1>::value_type>)
5436       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5437 	    typename iterator_traits<_InputIterator1>::value_type,
5438 	    typename iterator_traits<_InputIterator2>::value_type>)
5439       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5440 	    typename iterator_traits<_InputIterator2>::value_type,
5441 	    typename iterator_traits<_InputIterator1>::value_type>)
5442       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5443       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5444       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5445       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5446 
5447       return _GLIBCXX_STD_A::__set_difference(__first1, __last1,
5448 				   __first2, __last2, __result,
5449 				   __gnu_cxx::__ops::__iter_comp_iter(__comp));
5450     }
5451 
5452   template<typename _InputIterator1, typename _InputIterator2,
5453 	   typename _OutputIterator,
5454 	   typename _Compare>
5455     _OutputIterator
5456     __set_symmetric_difference(_InputIterator1 __first1,
5457 			       _InputIterator1 __last1,
5458 			       _InputIterator2 __first2,
5459 			       _InputIterator2 __last2,
5460 			       _OutputIterator __result,
5461 			       _Compare __comp)
5462     {
5463       while (__first1 != __last1 && __first2 != __last2)
5464 	if (__comp(__first1, __first2))
5465 	  {
5466 	    *__result = *__first1;
5467 	    ++__first1;
5468 	    ++__result;
5469 	  }
5470 	else if (__comp(__first2, __first1))
5471 	  {
5472 	    *__result = *__first2;
5473 	    ++__first2;
5474 	    ++__result;
5475 	  }
5476 	else
5477 	  {
5478 	    ++__first1;
5479 	    ++__first2;
5480 	  }
5481       return std::copy(__first2, __last2,
5482 		       std::copy(__first1, __last1, __result));
5483     }
5484 
5485   /**
5486    *  @brief  Return the symmetric difference of two sorted ranges.
5487    *  @ingroup set_algorithms
5488    *  @param  __first1  Start of first range.
5489    *  @param  __last1   End of first range.
5490    *  @param  __first2  Start of second range.
5491    *  @param  __last2   End of second range.
5492    *  @param  __result  Start of output range.
5493    *  @return  End of the output range.
5494    *  @ingroup set_algorithms
5495    *
5496    *  This operation iterates over both ranges, copying elements present in
5497    *  one range but not the other in order to the output range.  Iterators
5498    *  increment for each range.  When the current element of one range is less
5499    *  than the other, that element is copied and the iterator advances.  If an
5500    *  element is contained in both ranges, no elements are copied and both
5501    *  ranges advance.  The output range may not overlap either input range.
5502   */
5503   template<typename _InputIterator1, typename _InputIterator2,
5504 	   typename _OutputIterator>
5505     inline _OutputIterator
5506     set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5507 			     _InputIterator2 __first2, _InputIterator2 __last2,
5508 			     _OutputIterator __result)
5509     {
5510       // concept requirements
5511       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5512       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5513       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5514 	    typename iterator_traits<_InputIterator1>::value_type>)
5515       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5516 	    typename iterator_traits<_InputIterator2>::value_type>)
5517       __glibcxx_function_requires(_LessThanOpConcept<
5518 	    typename iterator_traits<_InputIterator1>::value_type,
5519 	    typename iterator_traits<_InputIterator2>::value_type>)
5520       __glibcxx_function_requires(_LessThanOpConcept<
5521 	    typename iterator_traits<_InputIterator2>::value_type,
5522 	    typename iterator_traits<_InputIterator1>::value_type>)
5523       __glibcxx_requires_sorted_set(__first1, __last1, __first2);
5524       __glibcxx_requires_sorted_set(__first2, __last2, __first1);
5525       __glibcxx_requires_irreflexive2(__first1, __last1);
5526       __glibcxx_requires_irreflexive2(__first2, __last2);
5527 
5528       return _GLIBCXX_STD_A::__set_symmetric_difference(__first1, __last1,
5529 					__first2, __last2, __result,
5530 					__gnu_cxx::__ops::__iter_less_iter());
5531     }
5532 
5533   /**
5534    *  @brief  Return the symmetric difference of two sorted ranges using
5535    *  comparison functor.
5536    *  @ingroup set_algorithms
5537    *  @param  __first1  Start of first range.
5538    *  @param  __last1   End of first range.
5539    *  @param  __first2  Start of second range.
5540    *  @param  __last2   End of second range.
5541    *  @param  __result  Start of output range.
5542    *  @param  __comp    The comparison functor.
5543    *  @return  End of the output range.
5544    *  @ingroup set_algorithms
5545    *
5546    *  This operation iterates over both ranges, copying elements present in
5547    *  one range but not the other in order to the output range.  Iterators
5548    *  increment for each range.  When the current element of one range is less
5549    *  than the other according to @p comp, that element is copied and the
5550    *  iterator advances.  If an element is contained in both ranges according
5551    *  to @p __comp, no elements are copied and both ranges advance.  The output
5552    *  range may not overlap either input range.
5553   */
5554   template<typename _InputIterator1, typename _InputIterator2,
5555 	   typename _OutputIterator, typename _Compare>
5556     inline _OutputIterator
5557     set_symmetric_difference(_InputIterator1 __first1, _InputIterator1 __last1,
5558 			     _InputIterator2 __first2, _InputIterator2 __last2,
5559 			     _OutputIterator __result,
5560 			     _Compare __comp)
5561     {
5562       // concept requirements
5563       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
5564       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
5565       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5566 	    typename iterator_traits<_InputIterator1>::value_type>)
5567       __glibcxx_function_requires(_OutputIteratorConcept<_OutputIterator,
5568 	    typename iterator_traits<_InputIterator2>::value_type>)
5569       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5570 	    typename iterator_traits<_InputIterator1>::value_type,
5571 	    typename iterator_traits<_InputIterator2>::value_type>)
5572       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5573 	    typename iterator_traits<_InputIterator2>::value_type,
5574 	    typename iterator_traits<_InputIterator1>::value_type>)
5575       __glibcxx_requires_sorted_set_pred(__first1, __last1, __first2, __comp);
5576       __glibcxx_requires_sorted_set_pred(__first2, __last2, __first1, __comp);
5577       __glibcxx_requires_irreflexive_pred2(__first1, __last1, __comp);
5578       __glibcxx_requires_irreflexive_pred2(__first2, __last2, __comp);
5579 
5580       return _GLIBCXX_STD_A::__set_symmetric_difference(__first1, __last1,
5581 				__first2, __last2, __result,
5582 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
5583     }
5584 
5585   template<typename _ForwardIterator, typename _Compare>
5586     _GLIBCXX14_CONSTEXPR
5587     _ForwardIterator
5588     __min_element(_ForwardIterator __first, _ForwardIterator __last,
5589 		  _Compare __comp)
5590     {
5591       if (__first == __last)
5592 	return __first;
5593       _ForwardIterator __result = __first;
5594       while (++__first != __last)
5595 	if (__comp(__first, __result))
5596 	  __result = __first;
5597       return __result;
5598     }
5599 
5600   /**
5601    *  @brief  Return the minimum element in a range.
5602    *  @ingroup sorting_algorithms
5603    *  @param  __first  Start of range.
5604    *  @param  __last   End of range.
5605    *  @return  Iterator referencing the first instance of the smallest value.
5606   */
5607   template<typename _ForwardIterator>
5608     _GLIBCXX14_CONSTEXPR
5609     _ForwardIterator
5610     inline min_element(_ForwardIterator __first, _ForwardIterator __last)
5611     {
5612       // concept requirements
5613       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5614       __glibcxx_function_requires(_LessThanComparableConcept<
5615 	    typename iterator_traits<_ForwardIterator>::value_type>)
5616       __glibcxx_requires_valid_range(__first, __last);
5617       __glibcxx_requires_irreflexive(__first, __last);
5618 
5619       return _GLIBCXX_STD_A::__min_element(__first, __last,
5620 				__gnu_cxx::__ops::__iter_less_iter());
5621     }
5622 
5623   /**
5624    *  @brief  Return the minimum element in a range using comparison functor.
5625    *  @ingroup sorting_algorithms
5626    *  @param  __first  Start of range.
5627    *  @param  __last   End of range.
5628    *  @param  __comp   Comparison functor.
5629    *  @return  Iterator referencing the first instance of the smallest value
5630    *  according to __comp.
5631   */
5632   template<typename _ForwardIterator, typename _Compare>
5633     _GLIBCXX14_CONSTEXPR
5634     inline _ForwardIterator
5635     min_element(_ForwardIterator __first, _ForwardIterator __last,
5636 		_Compare __comp)
5637     {
5638       // concept requirements
5639       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5640       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5641 	    typename iterator_traits<_ForwardIterator>::value_type,
5642 	    typename iterator_traits<_ForwardIterator>::value_type>)
5643       __glibcxx_requires_valid_range(__first, __last);
5644       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5645 
5646       return _GLIBCXX_STD_A::__min_element(__first, __last,
5647 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
5648     }
5649 
5650   template<typename _ForwardIterator, typename _Compare>
5651     _GLIBCXX14_CONSTEXPR
5652     _ForwardIterator
5653     __max_element(_ForwardIterator __first, _ForwardIterator __last,
5654 		  _Compare __comp)
5655     {
5656       if (__first == __last) return __first;
5657       _ForwardIterator __result = __first;
5658       while (++__first != __last)
5659 	if (__comp(__result, __first))
5660 	  __result = __first;
5661       return __result;
5662     }
5663 
5664   /**
5665    *  @brief  Return the maximum element in a range.
5666    *  @ingroup sorting_algorithms
5667    *  @param  __first  Start of range.
5668    *  @param  __last   End of range.
5669    *  @return  Iterator referencing the first instance of the largest value.
5670   */
5671   template<typename _ForwardIterator>
5672     _GLIBCXX14_CONSTEXPR
5673     inline _ForwardIterator
5674     max_element(_ForwardIterator __first, _ForwardIterator __last)
5675     {
5676       // concept requirements
5677       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5678       __glibcxx_function_requires(_LessThanComparableConcept<
5679 	    typename iterator_traits<_ForwardIterator>::value_type>)
5680       __glibcxx_requires_valid_range(__first, __last);
5681       __glibcxx_requires_irreflexive(__first, __last);
5682 
5683       return _GLIBCXX_STD_A::__max_element(__first, __last,
5684 				__gnu_cxx::__ops::__iter_less_iter());
5685     }
5686 
5687   /**
5688    *  @brief  Return the maximum element in a range using comparison functor.
5689    *  @ingroup sorting_algorithms
5690    *  @param  __first  Start of range.
5691    *  @param  __last   End of range.
5692    *  @param  __comp   Comparison functor.
5693    *  @return  Iterator referencing the first instance of the largest value
5694    *  according to __comp.
5695   */
5696   template<typename _ForwardIterator, typename _Compare>
5697     _GLIBCXX14_CONSTEXPR
5698     inline _ForwardIterator
5699     max_element(_ForwardIterator __first, _ForwardIterator __last,
5700 		_Compare __comp)
5701     {
5702       // concept requirements
5703       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
5704       __glibcxx_function_requires(_BinaryPredicateConcept<_Compare,
5705 	    typename iterator_traits<_ForwardIterator>::value_type,
5706 	    typename iterator_traits<_ForwardIterator>::value_type>)
5707       __glibcxx_requires_valid_range(__first, __last);
5708       __glibcxx_requires_irreflexive_pred(__first, __last, __comp);
5709 
5710       return _GLIBCXX_STD_A::__max_element(__first, __last,
5711 				__gnu_cxx::__ops::__iter_comp_iter(__comp));
5712     }
5713 
5714 #if __cplusplus >= 201402L
5715   /// Reservoir sampling algorithm.
5716   template<typename _InputIterator, typename _RandomAccessIterator,
5717            typename _Size, typename _UniformRandomBitGenerator>
5718     _RandomAccessIterator
5719     __sample(_InputIterator __first, _InputIterator __last, input_iterator_tag,
5720 	     _RandomAccessIterator __out, random_access_iterator_tag,
5721 	     _Size __n, _UniformRandomBitGenerator&& __g)
5722     {
5723       using __distrib_type = uniform_int_distribution<_Size>;
5724       using __param_type = typename __distrib_type::param_type;
5725       __distrib_type __d{};
5726       _Size __sample_sz = 0;
5727       while (__first != __last && __sample_sz != __n)
5728 	{
5729 	  __out[__sample_sz++] = *__first;
5730 	  ++__first;
5731 	}
5732       for (auto __pop_sz = __sample_sz; __first != __last;
5733 	  ++__first, (void) ++__pop_sz)
5734 	{
5735 	  const auto __k = __d(__g, __param_type{0, __pop_sz});
5736 	  if (__k < __n)
5737 	    __out[__k] = *__first;
5738 	}
5739       return __out + __sample_sz;
5740     }
5741 
5742   /// Selection sampling algorithm.
5743   template<typename _ForwardIterator, typename _OutputIterator, typename _Cat,
5744            typename _Size, typename _UniformRandomBitGenerator>
5745     _OutputIterator
5746     __sample(_ForwardIterator __first, _ForwardIterator __last,
5747 	     forward_iterator_tag,
5748 	     _OutputIterator __out, _Cat,
5749 	     _Size __n, _UniformRandomBitGenerator&& __g)
5750     {
5751       using __distrib_type = uniform_int_distribution<_Size>;
5752       using __param_type = typename __distrib_type::param_type;
5753       using _USize = make_unsigned_t<_Size>;
5754       using _Gen = remove_reference_t<_UniformRandomBitGenerator>;
5755       using __uc_type = common_type_t<typename _Gen::result_type, _USize>;
5756 
5757       __distrib_type __d{};
5758       _Size __unsampled_sz = std::distance(__first, __last);
5759       __n = std::min(__n, __unsampled_sz);
5760 
5761       // If possible, we use __gen_two_uniform_ints to efficiently produce
5762       // two random numbers using a single distribution invocation:
5763 
5764       const __uc_type __urngrange = __g.max() - __g.min();
5765       if (__urngrange / __uc_type(__unsampled_sz) >= __uc_type(__unsampled_sz))
5766         // I.e. (__urngrange >= __unsampled_sz * __unsampled_sz) but without
5767 	// wrapping issues.
5768         {
5769 	  while (__n != 0 && __unsampled_sz >= 2)
5770 	    {
5771 	      const pair<_Size, _Size> __p =
5772 		__gen_two_uniform_ints(__unsampled_sz, __unsampled_sz - 1, __g);
5773 
5774 	      --__unsampled_sz;
5775 	      if (__p.first < __n)
5776 		{
5777 		  *__out++ = *__first;
5778 		  --__n;
5779 		}
5780 
5781 	      ++__first;
5782 
5783 	      if (__n == 0) break;
5784 
5785 	      --__unsampled_sz;
5786 	      if (__p.second < __n)
5787 		{
5788 		  *__out++ = *__first;
5789 		  --__n;
5790 		}
5791 
5792 	      ++__first;
5793 	    }
5794         }
5795 
5796       // The loop above is otherwise equivalent to this one-at-a-time version:
5797 
5798       for (; __n != 0; ++__first)
5799 	if (__d(__g, __param_type{0, --__unsampled_sz}) < __n)
5800 	  {
5801 	    *__out++ = *__first;
5802 	    --__n;
5803 	  }
5804       return __out;
5805     }
5806 
5807 #if __cplusplus > 201402L
5808 #define __cpp_lib_sample 201603
5809   /// Take a random sample from a population.
5810   template<typename _PopulationIterator, typename _SampleIterator,
5811            typename _Distance, typename _UniformRandomBitGenerator>
5812     _SampleIterator
5813     sample(_PopulationIterator __first, _PopulationIterator __last,
5814 	   _SampleIterator __out, _Distance __n,
5815 	   _UniformRandomBitGenerator&& __g)
5816     {
5817       using __pop_cat = typename
5818 	std::iterator_traits<_PopulationIterator>::iterator_category;
5819       using __samp_cat = typename
5820 	std::iterator_traits<_SampleIterator>::iterator_category;
5821 
5822       static_assert(
5823 	  __or_<is_convertible<__pop_cat, forward_iterator_tag>,
5824 		is_convertible<__samp_cat, random_access_iterator_tag>>::value,
5825 	  "output range must use a RandomAccessIterator when input range"
5826 	  " does not meet the ForwardIterator requirements");
5827 
5828       static_assert(is_integral<_Distance>::value,
5829 		    "sample size must be an integer type");
5830 
5831       typename iterator_traits<_PopulationIterator>::difference_type __d = __n;
5832       return _GLIBCXX_STD_A::
5833 	__sample(__first, __last, __pop_cat{}, __out, __samp_cat{}, __d,
5834 		 std::forward<_UniformRandomBitGenerator>(__g));
5835     }
5836 #endif // C++17
5837 #endif // C++14
5838 
5839 _GLIBCXX_END_NAMESPACE_ALGO
5840 _GLIBCXX_END_NAMESPACE_VERSION
5841 } // namespace std
5842 
5843 #endif /* _STL_ALGO_H */
5844