1 // Core algorithmic facilities -*- 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) 1996-1998
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_algobase.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_ALGOBASE_H
57 #define _STL_ALGOBASE_H 1
58 
59 #include <bits/c++config.h>
60 #include <bits/functexcept.h>
61 #include <bits/cpp_type_traits.h>
62 #include <ext/type_traits.h>
63 #include <ext/numeric_traits.h>
64 #include <bits/stl_pair.h>
65 #include <bits/stl_iterator_base_types.h>
66 #include <bits/stl_iterator_base_funcs.h>
67 #include <bits/stl_iterator.h>
68 #include <bits/concept_check.h>
69 #include <debug/debug.h>
70 #include <bits/move.h> // For std::swap
71 #include <bits/predefined_ops.h>
72 
_GLIBCXX_VISIBILITY(default)73 namespace std _GLIBCXX_VISIBILITY(default)
74 {
75 _GLIBCXX_BEGIN_NAMESPACE_VERSION
76 
77 #if __cplusplus < 201103L
78   // See http://gcc.gnu.org/ml/libstdc++/2004-08/msg00167.html: in a
79   // nutshell, we are partially implementing the resolution of DR 187,
80   // when it's safe, i.e., the value_types are equal.
81   template<bool _BoolType>
82     struct __iter_swap
83     {
84       template<typename _ForwardIterator1, typename _ForwardIterator2>
85 	static void
86 	iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
87 	{
88 	  typedef typename iterator_traits<_ForwardIterator1>::value_type
89 	    _ValueType1;
90 	  _ValueType1 __tmp = *__a;
91 	  *__a = *__b;
92 	  *__b = __tmp;
93 	}
94     };
95 
96   template<>
97     struct __iter_swap<true>
98     {
99       template<typename _ForwardIterator1, typename _ForwardIterator2>
100 	static void
101 	iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
102 	{
103 	  swap(*__a, *__b);
104 	}
105     };
106 #endif
107 
108   /**
109    *  @brief Swaps the contents of two iterators.
110    *  @ingroup mutating_algorithms
111    *  @param  __a  An iterator.
112    *  @param  __b  Another iterator.
113    *  @return   Nothing.
114    *
115    *  This function swaps the values pointed to by two iterators, not the
116    *  iterators themselves.
117   */
118   template<typename _ForwardIterator1, typename _ForwardIterator2>
119     inline void
120     iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
121     {
122       // concept requirements
123       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
124 				  _ForwardIterator1>)
125       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
126 				  _ForwardIterator2>)
127 
128 #if __cplusplus < 201103L
129       typedef typename iterator_traits<_ForwardIterator1>::value_type
130 	_ValueType1;
131       typedef typename iterator_traits<_ForwardIterator2>::value_type
132 	_ValueType2;
133 
134       __glibcxx_function_requires(_ConvertibleConcept<_ValueType1,
135 				  _ValueType2>)
136       __glibcxx_function_requires(_ConvertibleConcept<_ValueType2,
137 				  _ValueType1>)
138 
139       typedef typename iterator_traits<_ForwardIterator1>::reference
140 	_ReferenceType1;
141       typedef typename iterator_traits<_ForwardIterator2>::reference
142 	_ReferenceType2;
143       std::__iter_swap<__are_same<_ValueType1, _ValueType2>::__value
144 	&& __are_same<_ValueType1&, _ReferenceType1>::__value
145 	&& __are_same<_ValueType2&, _ReferenceType2>::__value>::
146 	iter_swap(__a, __b);
147 #else
148       swap(*__a, *__b);
149 #endif
150     }
151 
152   /**
153    *  @brief Swap the elements of two sequences.
154    *  @ingroup mutating_algorithms
155    *  @param  __first1  A forward iterator.
156    *  @param  __last1   A forward iterator.
157    *  @param  __first2  A forward iterator.
158    *  @return   An iterator equal to @p first2+(last1-first1).
159    *
160    *  Swaps each element in the range @p [first1,last1) with the
161    *  corresponding element in the range @p [first2,(last1-first1)).
162    *  The ranges must not overlap.
163   */
164   template<typename _ForwardIterator1, typename _ForwardIterator2>
165     _ForwardIterator2
166     swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
167 		_ForwardIterator2 __first2)
168     {
169       // concept requirements
170       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
171 				  _ForwardIterator1>)
172       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
173 				  _ForwardIterator2>)
174       __glibcxx_requires_valid_range(__first1, __last1);
175 
176       for (; __first1 != __last1; ++__first1, (void)++__first2)
177 	std::iter_swap(__first1, __first2);
178       return __first2;
179     }
180 
181   /**
182    *  @brief This does what you think it does.
183    *  @ingroup sorting_algorithms
184    *  @param  __a  A thing of arbitrary type.
185    *  @param  __b  Another thing of arbitrary type.
186    *  @return   The lesser of the parameters.
187    *
188    *  This is the simple classic generic implementation.  It will work on
189    *  temporary expressions, since they are only evaluated once, unlike a
190    *  preprocessor macro.
191   */
192   template<typename _Tp>
193     _GLIBCXX14_CONSTEXPR
194     inline const _Tp&
195     min(const _Tp& __a, const _Tp& __b)
196     {
197       // concept requirements
198       __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
199       //return __b < __a ? __b : __a;
200       if (__b < __a)
201 	return __b;
202       return __a;
203     }
204 
205   /**
206    *  @brief This does what you think it does.
207    *  @ingroup sorting_algorithms
208    *  @param  __a  A thing of arbitrary type.
209    *  @param  __b  Another thing of arbitrary type.
210    *  @return   The greater of the parameters.
211    *
212    *  This is the simple classic generic implementation.  It will work on
213    *  temporary expressions, since they are only evaluated once, unlike a
214    *  preprocessor macro.
215   */
216   template<typename _Tp>
217     _GLIBCXX14_CONSTEXPR
218     inline const _Tp&
219     max(const _Tp& __a, const _Tp& __b)
220     {
221       // concept requirements
222       __glibcxx_function_requires(_LessThanComparableConcept<_Tp>)
223       //return  __a < __b ? __b : __a;
224       if (__a < __b)
225 	return __b;
226       return __a;
227     }
228 
229   /**
230    *  @brief This does what you think it does.
231    *  @ingroup sorting_algorithms
232    *  @param  __a  A thing of arbitrary type.
233    *  @param  __b  Another thing of arbitrary type.
234    *  @param  __comp  A @link comparison_functors comparison functor@endlink.
235    *  @return   The lesser of the parameters.
236    *
237    *  This will work on temporary expressions, since they are only evaluated
238    *  once, unlike a preprocessor macro.
239   */
240   template<typename _Tp, typename _Compare>
241     _GLIBCXX14_CONSTEXPR
242     inline const _Tp&
243     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
244     {
245       //return __comp(__b, __a) ? __b : __a;
246       if (__comp(__b, __a))
247 	return __b;
248       return __a;
249     }
250 
251   /**
252    *  @brief This does what you think it does.
253    *  @ingroup sorting_algorithms
254    *  @param  __a  A thing of arbitrary type.
255    *  @param  __b  Another thing of arbitrary type.
256    *  @param  __comp  A @link comparison_functors comparison functor@endlink.
257    *  @return   The greater of the parameters.
258    *
259    *  This will work on temporary expressions, since they are only evaluated
260    *  once, unlike a preprocessor macro.
261   */
262   template<typename _Tp, typename _Compare>
263     _GLIBCXX14_CONSTEXPR
264     inline const _Tp&
265     max(const _Tp& __a, const _Tp& __b, _Compare __comp)
266     {
267       //return __comp(__a, __b) ? __b : __a;
268       if (__comp(__a, __b))
269 	return __b;
270       return __a;
271     }
272 
273   // Fallback implementation of the function in bits/stl_iterator.h used to
274   // remove the __normal_iterator wrapper. See copy, fill, ...
275   template<typename _Iterator>
276     inline _Iterator
277     __niter_base(_Iterator __it)
278     { return __it; }
279 
280   // All of these auxiliary structs serve two purposes.  (1) Replace
281   // calls to copy with memmove whenever possible.  (Memmove, not memcpy,
282   // because the input and output ranges are permitted to overlap.)
283   // (2) If we're using random access iterators, then write the loop as
284   // a for loop with an explicit count.
285 
286   template<bool, bool, typename>
287     struct __copy_move
288     {
289       template<typename _II, typename _OI>
290 	static _OI
291 	__copy_m(_II __first, _II __last, _OI __result)
292 	{
293 	  for (; __first != __last; ++__result, (void)++__first)
294 	    *__result = *__first;
295 	  return __result;
296 	}
297     };
298 
299 #if __cplusplus >= 201103L
300   template<typename _Category>
301     struct __copy_move<true, false, _Category>
302     {
303       template<typename _II, typename _OI>
304 	static _OI
305 	__copy_m(_II __first, _II __last, _OI __result)
306 	{
307 	  for (; __first != __last; ++__result, (void)++__first)
308 	    *__result = std::move(*__first);
309 	  return __result;
310 	}
311     };
312 #endif
313 
314   template<>
315     struct __copy_move<false, false, random_access_iterator_tag>
316     {
317       template<typename _II, typename _OI>
318 	static _OI
319 	__copy_m(_II __first, _II __last, _OI __result)
320 	{
321 	  typedef typename iterator_traits<_II>::difference_type _Distance;
322 	  for(_Distance __n = __last - __first; __n > 0; --__n)
323 	    {
324 	      *__result = *__first;
325 	      ++__first;
326 	      ++__result;
327 	    }
328 	  return __result;
329 	}
330     };
331 
332 #if __cplusplus >= 201103L
333   template<>
334     struct __copy_move<true, false, random_access_iterator_tag>
335     {
336       template<typename _II, typename _OI>
337 	static _OI
338 	__copy_m(_II __first, _II __last, _OI __result)
339 	{
340 	  typedef typename iterator_traits<_II>::difference_type _Distance;
341 	  for(_Distance __n = __last - __first; __n > 0; --__n)
342 	    {
343 	      *__result = std::move(*__first);
344 	      ++__first;
345 	      ++__result;
346 	    }
347 	  return __result;
348 	}
349     };
350 #endif
351 
352   template<bool _IsMove>
353     struct __copy_move<_IsMove, true, random_access_iterator_tag>
354     {
355       template<typename _Tp>
356 	static _Tp*
357 	__copy_m(const _Tp* __first, const _Tp* __last, _Tp* __result)
358 	{
359 #if __cplusplus >= 201103L
360 	  using __assignable = conditional<_IsMove,
361 					   is_move_assignable<_Tp>,
362 					   is_copy_assignable<_Tp>>;
363 	  // trivial types can have deleted assignment
364 	  static_assert( __assignable::type::value, "type is not assignable" );
365 #endif
366 	  const ptrdiff_t _Num = __last - __first;
367 	  if (_Num)
368 	    __builtin_memmove(__result, __first, sizeof(_Tp) * _Num);
369 	  return __result + _Num;
370 	}
371     };
372 
373   template<bool _IsMove, typename _II, typename _OI>
374     inline _OI
375     __copy_move_a(_II __first, _II __last, _OI __result)
376     {
377       typedef typename iterator_traits<_II>::value_type _ValueTypeI;
378       typedef typename iterator_traits<_OI>::value_type _ValueTypeO;
379       typedef typename iterator_traits<_II>::iterator_category _Category;
380       const bool __simple = (__is_trivial(_ValueTypeI)
381 			     && __is_pointer<_II>::__value
382 			     && __is_pointer<_OI>::__value
383 			     && __are_same<_ValueTypeI, _ValueTypeO>::__value);
384 
385       return std::__copy_move<_IsMove, __simple,
386 			      _Category>::__copy_m(__first, __last, __result);
387     }
388 
389   // Helpers for streambuf iterators (either istream or ostream).
390   // NB: avoid including <iosfwd>, relatively large.
391   template<typename _CharT>
392     struct char_traits;
393 
394   template<typename _CharT, typename _Traits>
395     class istreambuf_iterator;
396 
397   template<typename _CharT, typename _Traits>
398     class ostreambuf_iterator;
399 
400   template<bool _IsMove, typename _CharT>
401     typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value,
402 	     ostreambuf_iterator<_CharT, char_traits<_CharT> > >::__type
403     __copy_move_a2(_CharT*, _CharT*,
404 		   ostreambuf_iterator<_CharT, char_traits<_CharT> >);
405 
406   template<bool _IsMove, typename _CharT>
407     typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value,
408 	     ostreambuf_iterator<_CharT, char_traits<_CharT> > >::__type
409     __copy_move_a2(const _CharT*, const _CharT*,
410 		   ostreambuf_iterator<_CharT, char_traits<_CharT> >);
411 
412   template<bool _IsMove, typename _CharT>
413     typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value,
414 				    _CharT*>::__type
415     __copy_move_a2(istreambuf_iterator<_CharT, char_traits<_CharT> >,
416 		   istreambuf_iterator<_CharT, char_traits<_CharT> >, _CharT*);
417 
418   template<bool _IsMove, typename _II, typename _OI>
419     inline _OI
420     __copy_move_a2(_II __first, _II __last, _OI __result)
421     {
422       return _OI(std::__copy_move_a<_IsMove>(std::__niter_base(__first),
423 					     std::__niter_base(__last),
424 					     std::__niter_base(__result)));
425     }
426 
427   /**
428    *  @brief Copies the range [first,last) into result.
429    *  @ingroup mutating_algorithms
430    *  @param  __first  An input iterator.
431    *  @param  __last   An input iterator.
432    *  @param  __result An output iterator.
433    *  @return   result + (first - last)
434    *
435    *  This inline function will boil down to a call to @c memmove whenever
436    *  possible.  Failing that, if random access iterators are passed, then the
437    *  loop count will be known (and therefore a candidate for compiler
438    *  optimizations such as unrolling).  Result may not be contained within
439    *  [first,last); the copy_backward function should be used instead.
440    *
441    *  Note that the end of the output range is permitted to be contained
442    *  within [first,last).
443   */
444   template<typename _II, typename _OI>
445     inline _OI
446     copy(_II __first, _II __last, _OI __result)
447     {
448       // concept requirements
449       __glibcxx_function_requires(_InputIteratorConcept<_II>)
450       __glibcxx_function_requires(_OutputIteratorConcept<_OI,
451 	    typename iterator_traits<_II>::value_type>)
452       __glibcxx_requires_valid_range(__first, __last);
453 
454       return (std::__copy_move_a2<__is_move_iterator<_II>::__value>
455 	      (std::__miter_base(__first), std::__miter_base(__last),
456 	       __result));
457     }
458 
459 #if __cplusplus >= 201103L
460   /**
461    *  @brief Moves the range [first,last) into result.
462    *  @ingroup mutating_algorithms
463    *  @param  __first  An input iterator.
464    *  @param  __last   An input iterator.
465    *  @param  __result An output iterator.
466    *  @return   result + (first - last)
467    *
468    *  This inline function will boil down to a call to @c memmove whenever
469    *  possible.  Failing that, if random access iterators are passed, then the
470    *  loop count will be known (and therefore a candidate for compiler
471    *  optimizations such as unrolling).  Result may not be contained within
472    *  [first,last); the move_backward function should be used instead.
473    *
474    *  Note that the end of the output range is permitted to be contained
475    *  within [first,last).
476   */
477   template<typename _II, typename _OI>
478     inline _OI
479     move(_II __first, _II __last, _OI __result)
480     {
481       // concept requirements
482       __glibcxx_function_requires(_InputIteratorConcept<_II>)
483       __glibcxx_function_requires(_OutputIteratorConcept<_OI,
484 	    typename iterator_traits<_II>::value_type>)
485       __glibcxx_requires_valid_range(__first, __last);
486 
487       return std::__copy_move_a2<true>(std::__miter_base(__first),
488 				       std::__miter_base(__last), __result);
489     }
490 
491 #define _GLIBCXX_MOVE3(_Tp, _Up, _Vp) std::move(_Tp, _Up, _Vp)
492 #else
493 #define _GLIBCXX_MOVE3(_Tp, _Up, _Vp) std::copy(_Tp, _Up, _Vp)
494 #endif
495 
496   template<bool, bool, typename>
497     struct __copy_move_backward
498     {
499       template<typename _BI1, typename _BI2>
500 	static _BI2
501 	__copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
502 	{
503 	  while (__first != __last)
504 	    *--__result = *--__last;
505 	  return __result;
506 	}
507     };
508 
509 #if __cplusplus >= 201103L
510   template<typename _Category>
511     struct __copy_move_backward<true, false, _Category>
512     {
513       template<typename _BI1, typename _BI2>
514 	static _BI2
515 	__copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
516 	{
517 	  while (__first != __last)
518 	    *--__result = std::move(*--__last);
519 	  return __result;
520 	}
521     };
522 #endif
523 
524   template<>
525     struct __copy_move_backward<false, false, random_access_iterator_tag>
526     {
527       template<typename _BI1, typename _BI2>
528 	static _BI2
529 	__copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
530 	{
531 	  typename iterator_traits<_BI1>::difference_type __n;
532 	  for (__n = __last - __first; __n > 0; --__n)
533 	    *--__result = *--__last;
534 	  return __result;
535 	}
536     };
537 
538 #if __cplusplus >= 201103L
539   template<>
540     struct __copy_move_backward<true, false, random_access_iterator_tag>
541     {
542       template<typename _BI1, typename _BI2>
543 	static _BI2
544 	__copy_move_b(_BI1 __first, _BI1 __last, _BI2 __result)
545 	{
546 	  typename iterator_traits<_BI1>::difference_type __n;
547 	  for (__n = __last - __first; __n > 0; --__n)
548 	    *--__result = std::move(*--__last);
549 	  return __result;
550 	}
551     };
552 #endif
553 
554   template<bool _IsMove>
555     struct __copy_move_backward<_IsMove, true, random_access_iterator_tag>
556     {
557       template<typename _Tp>
558 	static _Tp*
559 	__copy_move_b(const _Tp* __first, const _Tp* __last, _Tp* __result)
560 	{
561 #if __cplusplus >= 201103L
562 	  using __assignable = conditional<_IsMove,
563 					   is_move_assignable<_Tp>,
564 					   is_copy_assignable<_Tp>>;
565 	  // trivial types can have deleted assignment
566 	  static_assert( __assignable::type::value, "type is not assignable" );
567 #endif
568 	  const ptrdiff_t _Num = __last - __first;
569 	  if (_Num)
570 	    __builtin_memmove(__result - _Num, __first, sizeof(_Tp) * _Num);
571 	  return __result - _Num;
572 	}
573     };
574 
575   template<bool _IsMove, typename _BI1, typename _BI2>
576     inline _BI2
577     __copy_move_backward_a(_BI1 __first, _BI1 __last, _BI2 __result)
578     {
579       typedef typename iterator_traits<_BI1>::value_type _ValueType1;
580       typedef typename iterator_traits<_BI2>::value_type _ValueType2;
581       typedef typename iterator_traits<_BI1>::iterator_category _Category;
582       const bool __simple = (__is_trivial(_ValueType1)
583 			     && __is_pointer<_BI1>::__value
584 			     && __is_pointer<_BI2>::__value
585 			     && __are_same<_ValueType1, _ValueType2>::__value);
586 
587       return std::__copy_move_backward<_IsMove, __simple,
588 				       _Category>::__copy_move_b(__first,
589 								 __last,
590 								 __result);
591     }
592 
593   template<bool _IsMove, typename _BI1, typename _BI2>
594     inline _BI2
595     __copy_move_backward_a2(_BI1 __first, _BI1 __last, _BI2 __result)
596     {
597       return _BI2(std::__copy_move_backward_a<_IsMove>
598 		  (std::__niter_base(__first), std::__niter_base(__last),
599 		   std::__niter_base(__result)));
600     }
601 
602   /**
603    *  @brief Copies the range [first,last) into result.
604    *  @ingroup mutating_algorithms
605    *  @param  __first  A bidirectional iterator.
606    *  @param  __last   A bidirectional iterator.
607    *  @param  __result A bidirectional iterator.
608    *  @return   result - (first - last)
609    *
610    *  The function has the same effect as copy, but starts at the end of the
611    *  range and works its way to the start, returning the start of the result.
612    *  This inline function will boil down to a call to @c memmove whenever
613    *  possible.  Failing that, if random access iterators are passed, then the
614    *  loop count will be known (and therefore a candidate for compiler
615    *  optimizations such as unrolling).
616    *
617    *  Result may not be in the range (first,last].  Use copy instead.  Note
618    *  that the start of the output range may overlap [first,last).
619   */
620   template<typename _BI1, typename _BI2>
621     inline _BI2
622     copy_backward(_BI1 __first, _BI1 __last, _BI2 __result)
623     {
624       // concept requirements
625       __glibcxx_function_requires(_BidirectionalIteratorConcept<_BI1>)
626       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<_BI2>)
627       __glibcxx_function_requires(_ConvertibleConcept<
628 	    typename iterator_traits<_BI1>::value_type,
629 	    typename iterator_traits<_BI2>::value_type>)
630       __glibcxx_requires_valid_range(__first, __last);
631 
632       return (std::__copy_move_backward_a2<__is_move_iterator<_BI1>::__value>
633 	      (std::__miter_base(__first), std::__miter_base(__last),
634 	       __result));
635     }
636 
637 #if __cplusplus >= 201103L
638   /**
639    *  @brief Moves the range [first,last) into result.
640    *  @ingroup mutating_algorithms
641    *  @param  __first  A bidirectional iterator.
642    *  @param  __last   A bidirectional iterator.
643    *  @param  __result A bidirectional iterator.
644    *  @return   result - (first - last)
645    *
646    *  The function has the same effect as move, but starts at the end of the
647    *  range and works its way to the start, returning the start of the result.
648    *  This inline function will boil down to a call to @c memmove whenever
649    *  possible.  Failing that, if random access iterators are passed, then the
650    *  loop count will be known (and therefore a candidate for compiler
651    *  optimizations such as unrolling).
652    *
653    *  Result may not be in the range (first,last].  Use move instead.  Note
654    *  that the start of the output range may overlap [first,last).
655   */
656   template<typename _BI1, typename _BI2>
657     inline _BI2
658     move_backward(_BI1 __first, _BI1 __last, _BI2 __result)
659     {
660       // concept requirements
661       __glibcxx_function_requires(_BidirectionalIteratorConcept<_BI1>)
662       __glibcxx_function_requires(_Mutable_BidirectionalIteratorConcept<_BI2>)
663       __glibcxx_function_requires(_ConvertibleConcept<
664 	    typename iterator_traits<_BI1>::value_type,
665 	    typename iterator_traits<_BI2>::value_type>)
666       __glibcxx_requires_valid_range(__first, __last);
667 
668       return std::__copy_move_backward_a2<true>(std::__miter_base(__first),
669 						std::__miter_base(__last),
670 						__result);
671     }
672 
673 #define _GLIBCXX_MOVE_BACKWARD3(_Tp, _Up, _Vp) std::move_backward(_Tp, _Up, _Vp)
674 #else
675 #define _GLIBCXX_MOVE_BACKWARD3(_Tp, _Up, _Vp) std::copy_backward(_Tp, _Up, _Vp)
676 #endif
677 
678   template<typename _ForwardIterator, typename _Tp>
679     inline typename
680     __gnu_cxx::__enable_if<!__is_scalar<_Tp>::__value, void>::__type
681     __fill_a(_ForwardIterator __first, _ForwardIterator __last,
682  	     const _Tp& __value)
683     {
684       for (; __first != __last; ++__first)
685 	*__first = __value;
686     }
687 
688   template<typename _ForwardIterator, typename _Tp>
689     inline typename
690     __gnu_cxx::__enable_if<__is_scalar<_Tp>::__value, void>::__type
691     __fill_a(_ForwardIterator __first, _ForwardIterator __last,
692 	     const _Tp& __value)
693     {
694       const _Tp __tmp = __value;
695       for (; __first != __last; ++__first)
696 	*__first = __tmp;
697     }
698 
699   // Specialization: for char types we can use memset.
700   template<typename _Tp>
701     inline typename
702     __gnu_cxx::__enable_if<__is_byte<_Tp>::__value, void>::__type
703     __fill_a(_Tp* __first, _Tp* __last, const _Tp& __c)
704     {
705       const _Tp __tmp = __c;
706       if (const size_t __len = __last - __first)
707 	__builtin_memset(__first, static_cast<unsigned char>(__tmp), __len);
708     }
709 
710   /**
711    *  @brief Fills the range [first,last) with copies of value.
712    *  @ingroup mutating_algorithms
713    *  @param  __first  A forward iterator.
714    *  @param  __last   A forward iterator.
715    *  @param  __value  A reference-to-const of arbitrary type.
716    *  @return   Nothing.
717    *
718    *  This function fills a range with copies of the same value.  For char
719    *  types filling contiguous areas of memory, this becomes an inline call
720    *  to @c memset or @c wmemset.
721   */
722   template<typename _ForwardIterator, typename _Tp>
723     inline void
724     fill(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value)
725     {
726       // concept requirements
727       __glibcxx_function_requires(_Mutable_ForwardIteratorConcept<
728 				  _ForwardIterator>)
729       __glibcxx_requires_valid_range(__first, __last);
730 
731       std::__fill_a(std::__niter_base(__first), std::__niter_base(__last),
732 		    __value);
733     }
734 
735   template<typename _OutputIterator, typename _Size, typename _Tp>
736     inline typename
737     __gnu_cxx::__enable_if<!__is_scalar<_Tp>::__value, _OutputIterator>::__type
738     __fill_n_a(_OutputIterator __first, _Size __n, const _Tp& __value)
739     {
740       for (__decltype(__n + 0) __niter = __n;
741 	   __niter > 0; --__niter, (void) ++__first)
742 	*__first = __value;
743       return __first;
744     }
745 
746   template<typename _OutputIterator, typename _Size, typename _Tp>
747     inline typename
748     __gnu_cxx::__enable_if<__is_scalar<_Tp>::__value, _OutputIterator>::__type
749     __fill_n_a(_OutputIterator __first, _Size __n, const _Tp& __value)
750     {
751       const _Tp __tmp = __value;
752       for (__decltype(__n + 0) __niter = __n;
753 	   __niter > 0; --__niter, (void) ++__first)
754 	*__first = __tmp;
755       return __first;
756     }
757 
758   template<typename _Size, typename _Tp>
759     inline typename
760     __gnu_cxx::__enable_if<__is_byte<_Tp>::__value, _Tp*>::__type
761     __fill_n_a(_Tp* __first, _Size __n, const _Tp& __c)
762     {
763       std::__fill_a(__first, __first + __n, __c);
764       return __first + __n;
765     }
766 
767   /**
768    *  @brief Fills the range [first,first+n) with copies of value.
769    *  @ingroup mutating_algorithms
770    *  @param  __first  An output iterator.
771    *  @param  __n      The count of copies to perform.
772    *  @param  __value  A reference-to-const of arbitrary type.
773    *  @return   The iterator at first+n.
774    *
775    *  This function fills a range with copies of the same value.  For char
776    *  types filling contiguous areas of memory, this becomes an inline call
777    *  to @c memset or @ wmemset.
778    *
779    *  _GLIBCXX_RESOLVE_LIB_DEFECTS
780    *  DR 865. More algorithms that throw away information
781   */
782   template<typename _OI, typename _Size, typename _Tp>
783     inline _OI
784     fill_n(_OI __first, _Size __n, const _Tp& __value)
785     {
786       // concept requirements
787       __glibcxx_function_requires(_OutputIteratorConcept<_OI, _Tp>)
788 
789       return _OI(std::__fill_n_a(std::__niter_base(__first), __n, __value));
790     }
791 
792   template<bool _BoolType>
793     struct __equal
794     {
795       template<typename _II1, typename _II2>
796 	static bool
797 	equal(_II1 __first1, _II1 __last1, _II2 __first2)
798 	{
799 	  for (; __first1 != __last1; ++__first1, (void) ++__first2)
800 	    if (!(*__first1 == *__first2))
801 	      return false;
802 	  return true;
803 	}
804     };
805 
806   template<>
807     struct __equal<true>
808     {
809       template<typename _Tp>
810 	static bool
811 	equal(const _Tp* __first1, const _Tp* __last1, const _Tp* __first2)
812 	{
813 	  if (const size_t __len = (__last1 - __first1))
814 	    return !__builtin_memcmp(__first1, __first2, sizeof(_Tp) * __len);
815 	  return true;
816 	}
817     };
818 
819   template<typename _II1, typename _II2>
820     inline bool
821     __equal_aux(_II1 __first1, _II1 __last1, _II2 __first2)
822     {
823       typedef typename iterator_traits<_II1>::value_type _ValueType1;
824       typedef typename iterator_traits<_II2>::value_type _ValueType2;
825       const bool __simple = ((__is_integer<_ValueType1>::__value
826 			      || __is_pointer<_ValueType1>::__value)
827 			     && __is_pointer<_II1>::__value
828 			     && __is_pointer<_II2>::__value
829 			     && __are_same<_ValueType1, _ValueType2>::__value);
830 
831       return std::__equal<__simple>::equal(__first1, __last1, __first2);
832     }
833 
834   template<typename, typename>
835     struct __lc_rai
836     {
837       template<typename _II1, typename _II2>
838 	static _II1
839 	__newlast1(_II1, _II1 __last1, _II2, _II2)
840 	{ return __last1; }
841 
842       template<typename _II>
843 	static bool
844 	__cnd2(_II __first, _II __last)
845 	{ return __first != __last; }
846     };
847 
848   template<>
849     struct __lc_rai<random_access_iterator_tag, random_access_iterator_tag>
850     {
851       template<typename _RAI1, typename _RAI2>
852 	static _RAI1
853 	__newlast1(_RAI1 __first1, _RAI1 __last1,
854 		   _RAI2 __first2, _RAI2 __last2)
855 	{
856 	  const typename iterator_traits<_RAI1>::difference_type
857 	    __diff1 = __last1 - __first1;
858 	  const typename iterator_traits<_RAI2>::difference_type
859 	    __diff2 = __last2 - __first2;
860 	  return __diff2 < __diff1 ? __first1 + __diff2 : __last1;
861 	}
862 
863       template<typename _RAI>
864 	static bool
865 	__cnd2(_RAI, _RAI)
866 	{ return true; }
867     };
868 
869   template<typename _II1, typename _II2, typename _Compare>
870     bool
871     __lexicographical_compare_impl(_II1 __first1, _II1 __last1,
872 				   _II2 __first2, _II2 __last2,
873 				   _Compare __comp)
874     {
875       typedef typename iterator_traits<_II1>::iterator_category _Category1;
876       typedef typename iterator_traits<_II2>::iterator_category _Category2;
877       typedef std::__lc_rai<_Category1, _Category2> __rai_type;
878 
879       __last1 = __rai_type::__newlast1(__first1, __last1, __first2, __last2);
880       for (; __first1 != __last1 && __rai_type::__cnd2(__first2, __last2);
881 	   ++__first1, (void)++__first2)
882 	{
883 	  if (__comp(__first1, __first2))
884 	    return true;
885 	  if (__comp(__first2, __first1))
886 	    return false;
887 	}
888       return __first1 == __last1 && __first2 != __last2;
889     }
890 
891   template<bool _BoolType>
892     struct __lexicographical_compare
893     {
894       template<typename _II1, typename _II2>
895 	static bool __lc(_II1, _II1, _II2, _II2);
896     };
897 
898   template<bool _BoolType>
899     template<typename _II1, typename _II2>
900       bool
901       __lexicographical_compare<_BoolType>::
902       __lc(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
903       {
904 	return std::__lexicographical_compare_impl(__first1, __last1,
905 						   __first2, __last2,
906 					__gnu_cxx::__ops::__iter_less_iter());
907       }
908 
909   template<>
910     struct __lexicographical_compare<true>
911     {
912       template<typename _Tp, typename _Up>
913 	static bool
914 	__lc(const _Tp* __first1, const _Tp* __last1,
915 	     const _Up* __first2, const _Up* __last2)
916 	{
917 	  const size_t __len1 = __last1 - __first1;
918 	  const size_t __len2 = __last2 - __first2;
919 	  if (const size_t __len = std::min(__len1, __len2))
920 	    if (int __result = __builtin_memcmp(__first1, __first2, __len))
921 	      return __result < 0;
922 	  return __len1 < __len2;
923 	}
924     };
925 
926   template<typename _II1, typename _II2>
927     inline bool
928     __lexicographical_compare_aux(_II1 __first1, _II1 __last1,
929 				  _II2 __first2, _II2 __last2)
930     {
931       typedef typename iterator_traits<_II1>::value_type _ValueType1;
932       typedef typename iterator_traits<_II2>::value_type _ValueType2;
933       const bool __simple =
934 	(__is_byte<_ValueType1>::__value && __is_byte<_ValueType2>::__value
935 	 && !__gnu_cxx::__numeric_traits<_ValueType1>::__is_signed
936 	 && !__gnu_cxx::__numeric_traits<_ValueType2>::__is_signed
937 	 && __is_pointer<_II1>::__value
938 	 && __is_pointer<_II2>::__value);
939 
940       return std::__lexicographical_compare<__simple>::__lc(__first1, __last1,
941 							    __first2, __last2);
942     }
943 
944   template<typename _ForwardIterator, typename _Tp, typename _Compare>
945     _ForwardIterator
946     __lower_bound(_ForwardIterator __first, _ForwardIterator __last,
947 		  const _Tp& __val, _Compare __comp)
948     {
949       typedef typename iterator_traits<_ForwardIterator>::difference_type
950 	_DistanceType;
951 
952       _DistanceType __len = std::distance(__first, __last);
953 
954       while (__len > 0)
955 	{
956 	  _DistanceType __half = __len >> 1;
957 	  _ForwardIterator __middle = __first;
958 	  std::advance(__middle, __half);
959 	  if (__comp(__middle, __val))
960 	    {
961 	      __first = __middle;
962 	      ++__first;
963 	      __len = __len - __half - 1;
964 	    }
965 	  else
966 	    __len = __half;
967 	}
968       return __first;
969     }
970 
971   /**
972    *  @brief Finds the first position in which @a val could be inserted
973    *         without changing the ordering.
974    *  @param  __first   An iterator.
975    *  @param  __last    Another iterator.
976    *  @param  __val     The search term.
977    *  @return         An iterator pointing to the first element <em>not less
978    *                  than</em> @a val, or end() if every element is less than
979    *                  @a val.
980    *  @ingroup binary_search_algorithms
981   */
982   template<typename _ForwardIterator, typename _Tp>
983     inline _ForwardIterator
984     lower_bound(_ForwardIterator __first, _ForwardIterator __last,
985 		const _Tp& __val)
986     {
987       // concept requirements
988       __glibcxx_function_requires(_ForwardIteratorConcept<_ForwardIterator>)
989       __glibcxx_function_requires(_LessThanOpConcept<
990 	    typename iterator_traits<_ForwardIterator>::value_type, _Tp>)
991       __glibcxx_requires_partitioned_lower(__first, __last, __val);
992 
993       return std::__lower_bound(__first, __last, __val,
994 				__gnu_cxx::__ops::__iter_less_val());
995     }
996 
997   /// This is a helper function for the sort routines and for random.tcc.
998   //  Precondition: __n > 0.
999   inline _GLIBCXX_CONSTEXPR int
1000   __lg(int __n)
1001   { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
1002 
1003   inline _GLIBCXX_CONSTEXPR unsigned
1004   __lg(unsigned __n)
1005   { return (int)sizeof(int) * __CHAR_BIT__  - 1 - __builtin_clz(__n); }
1006 
1007   inline _GLIBCXX_CONSTEXPR long
1008   __lg(long __n)
1009   { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
1010 
1011   inline _GLIBCXX_CONSTEXPR unsigned long
1012   __lg(unsigned long __n)
1013   { return (int)sizeof(long) * __CHAR_BIT__ - 1 - __builtin_clzl(__n); }
1014 
1015   inline _GLIBCXX_CONSTEXPR long long
1016   __lg(long long __n)
1017   { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
1018 
1019   inline _GLIBCXX_CONSTEXPR unsigned long long
1020   __lg(unsigned long long __n)
1021   { return (int)sizeof(long long) * __CHAR_BIT__ - 1 - __builtin_clzll(__n); }
1022 
1023 _GLIBCXX_BEGIN_NAMESPACE_ALGO
1024 
1025   /**
1026    *  @brief Tests a range for element-wise equality.
1027    *  @ingroup non_mutating_algorithms
1028    *  @param  __first1  An input iterator.
1029    *  @param  __last1   An input iterator.
1030    *  @param  __first2  An input iterator.
1031    *  @return   A boolean true or false.
1032    *
1033    *  This compares the elements of two ranges using @c == and returns true or
1034    *  false depending on whether all of the corresponding elements of the
1035    *  ranges are equal.
1036   */
1037   template<typename _II1, typename _II2>
1038     inline bool
1039     equal(_II1 __first1, _II1 __last1, _II2 __first2)
1040     {
1041       // concept requirements
1042       __glibcxx_function_requires(_InputIteratorConcept<_II1>)
1043       __glibcxx_function_requires(_InputIteratorConcept<_II2>)
1044       __glibcxx_function_requires(_EqualOpConcept<
1045 	    typename iterator_traits<_II1>::value_type,
1046 	    typename iterator_traits<_II2>::value_type>)
1047       __glibcxx_requires_valid_range(__first1, __last1);
1048 
1049       return std::__equal_aux(std::__niter_base(__first1),
1050 			      std::__niter_base(__last1),
1051 			      std::__niter_base(__first2));
1052     }
1053 
1054   /**
1055    *  @brief Tests a range for element-wise equality.
1056    *  @ingroup non_mutating_algorithms
1057    *  @param  __first1  An input iterator.
1058    *  @param  __last1   An input iterator.
1059    *  @param  __first2  An input iterator.
1060    *  @param __binary_pred A binary predicate @link functors
1061    *                  functor@endlink.
1062    *  @return         A boolean true or false.
1063    *
1064    *  This compares the elements of two ranges using the binary_pred
1065    *  parameter, and returns true or
1066    *  false depending on whether all of the corresponding elements of the
1067    *  ranges are equal.
1068   */
1069   template<typename _IIter1, typename _IIter2, typename _BinaryPredicate>
1070     inline bool
1071     equal(_IIter1 __first1, _IIter1 __last1,
1072 	  _IIter2 __first2, _BinaryPredicate __binary_pred)
1073     {
1074       // concept requirements
1075       __glibcxx_function_requires(_InputIteratorConcept<_IIter1>)
1076       __glibcxx_function_requires(_InputIteratorConcept<_IIter2>)
1077       __glibcxx_requires_valid_range(__first1, __last1);
1078 
1079       for (; __first1 != __last1; ++__first1, (void)++__first2)
1080 	if (!bool(__binary_pred(*__first1, *__first2)))
1081 	  return false;
1082       return true;
1083     }
1084 
1085 #if __cplusplus >= 201103L
1086   // 4-iterator version of std::equal<It1, It2> for use in C++11.
1087   template<typename _II1, typename _II2>
1088     inline bool
1089     __equal4(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
1090     {
1091       using _RATag = random_access_iterator_tag;
1092       using _Cat1 = typename iterator_traits<_II1>::iterator_category;
1093       using _Cat2 = typename iterator_traits<_II2>::iterator_category;
1094       using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
1095       if (_RAIters())
1096 	{
1097 	  auto __d1 = std::distance(__first1, __last1);
1098 	  auto __d2 = std::distance(__first2, __last2);
1099 	  if (__d1 != __d2)
1100 	    return false;
1101 	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2);
1102 	}
1103 
1104       for (; __first1 != __last1 && __first2 != __last2;
1105 	  ++__first1, (void)++__first2)
1106 	if (!(*__first1 == *__first2))
1107 	  return false;
1108       return __first1 == __last1 && __first2 == __last2;
1109     }
1110 
1111   // 4-iterator version of std::equal<It1, It2, BinaryPred> for use in C++11.
1112   template<typename _II1, typename _II2, typename _BinaryPredicate>
1113     inline bool
1114     __equal4(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2,
1115 	     _BinaryPredicate __binary_pred)
1116     {
1117       using _RATag = random_access_iterator_tag;
1118       using _Cat1 = typename iterator_traits<_II1>::iterator_category;
1119       using _Cat2 = typename iterator_traits<_II2>::iterator_category;
1120       using _RAIters = __and_<is_same<_Cat1, _RATag>, is_same<_Cat2, _RATag>>;
1121       if (_RAIters())
1122 	{
1123 	  auto __d1 = std::distance(__first1, __last1);
1124 	  auto __d2 = std::distance(__first2, __last2);
1125 	  if (__d1 != __d2)
1126 	    return false;
1127 	  return _GLIBCXX_STD_A::equal(__first1, __last1, __first2,
1128 				       __binary_pred);
1129 	}
1130 
1131       for (; __first1 != __last1 && __first2 != __last2;
1132 	  ++__first1, (void)++__first2)
1133 	if (!bool(__binary_pred(*__first1, *__first2)))
1134 	  return false;
1135       return __first1 == __last1 && __first2 == __last2;
1136     }
1137 #endif // C++11
1138 
1139 #if __cplusplus > 201103L
1140 
1141 #define __cpp_lib_robust_nonmodifying_seq_ops 201304
1142 
1143   /**
1144    *  @brief Tests a range for element-wise equality.
1145    *  @ingroup non_mutating_algorithms
1146    *  @param  __first1  An input iterator.
1147    *  @param  __last1   An input iterator.
1148    *  @param  __first2  An input iterator.
1149    *  @param  __last2   An input iterator.
1150    *  @return   A boolean true or false.
1151    *
1152    *  This compares the elements of two ranges using @c == and returns true or
1153    *  false depending on whether all of the corresponding elements of the
1154    *  ranges are equal.
1155   */
1156   template<typename _II1, typename _II2>
1157     inline bool
1158     equal(_II1 __first1, _II1 __last1, _II2 __first2, _II2 __last2)
1159     {
1160       // concept requirements
1161       __glibcxx_function_requires(_InputIteratorConcept<_II1>)
1162       __glibcxx_function_requires(_InputIteratorConcept<_II2>)
1163       __glibcxx_function_requires(_EqualOpConcept<
1164 	    typename iterator_traits<_II1>::value_type,
1165 	    typename iterator_traits<_II2>::value_type>)
1166       __glibcxx_requires_valid_range(__first1, __last1);
1167       __glibcxx_requires_valid_range(__first2, __last2);
1168 
1169       return _GLIBCXX_STD_A::__equal4(__first1, __last1, __first2, __last2);
1170     }
1171 
1172   /**
1173    *  @brief Tests a range for element-wise equality.
1174    *  @ingroup non_mutating_algorithms
1175    *  @param  __first1  An input iterator.
1176    *  @param  __last1   An input iterator.
1177    *  @param  __first2  An input iterator.
1178    *  @param  __last2   An input iterator.
1179    *  @param __binary_pred A binary predicate @link functors
1180    *                  functor@endlink.
1181    *  @return         A boolean true or false.
1182    *
1183    *  This compares the elements of two ranges using the binary_pred
1184    *  parameter, and returns true or
1185    *  false depending on whether all of the corresponding elements of the
1186    *  ranges are equal.
1187   */
1188   template<typename _IIter1, typename _IIter2, typename _BinaryPredicate>
1189     inline bool
1190     equal(_IIter1 __first1, _IIter1 __last1,
1191 	  _IIter2 __first2, _IIter2 __last2, _BinaryPredicate __binary_pred)
1192     {
1193       // concept requirements
1194       __glibcxx_function_requires(_InputIteratorConcept<_IIter1>)
1195       __glibcxx_function_requires(_InputIteratorConcept<_IIter2>)
1196       __glibcxx_requires_valid_range(__first1, __last1);
1197       __glibcxx_requires_valid_range(__first2, __last2);
1198 
1199       return _GLIBCXX_STD_A::__equal4(__first1, __last1, __first2, __last2,
1200 				      __binary_pred);
1201     }
1202 #endif // C++14
1203 
1204   /**
1205    *  @brief Performs @b dictionary comparison on ranges.
1206    *  @ingroup sorting_algorithms
1207    *  @param  __first1  An input iterator.
1208    *  @param  __last1   An input iterator.
1209    *  @param  __first2  An input iterator.
1210    *  @param  __last2   An input iterator.
1211    *  @return   A boolean true or false.
1212    *
1213    *  <em>Returns true if the sequence of elements defined by the range
1214    *  [first1,last1) is lexicographically less than the sequence of elements
1215    *  defined by the range [first2,last2).  Returns false otherwise.</em>
1216    *  (Quoted from [25.3.8]/1.)  If the iterators are all character pointers,
1217    *  then this is an inline call to @c memcmp.
1218   */
1219   template<typename _II1, typename _II2>
1220     inline bool
1221     lexicographical_compare(_II1 __first1, _II1 __last1,
1222 			    _II2 __first2, _II2 __last2)
1223     {
1224 #ifdef _GLIBCXX_CONCEPT_CHECKS
1225       // concept requirements
1226       typedef typename iterator_traits<_II1>::value_type _ValueType1;
1227       typedef typename iterator_traits<_II2>::value_type _ValueType2;
1228 #endif
1229       __glibcxx_function_requires(_InputIteratorConcept<_II1>)
1230       __glibcxx_function_requires(_InputIteratorConcept<_II2>)
1231       __glibcxx_function_requires(_LessThanOpConcept<_ValueType1, _ValueType2>)
1232       __glibcxx_function_requires(_LessThanOpConcept<_ValueType2, _ValueType1>)
1233       __glibcxx_requires_valid_range(__first1, __last1);
1234       __glibcxx_requires_valid_range(__first2, __last2);
1235 
1236       return std::__lexicographical_compare_aux(std::__niter_base(__first1),
1237 						std::__niter_base(__last1),
1238 						std::__niter_base(__first2),
1239 						std::__niter_base(__last2));
1240     }
1241 
1242   /**
1243    *  @brief Performs @b dictionary comparison on ranges.
1244    *  @ingroup sorting_algorithms
1245    *  @param  __first1  An input iterator.
1246    *  @param  __last1   An input iterator.
1247    *  @param  __first2  An input iterator.
1248    *  @param  __last2   An input iterator.
1249    *  @param  __comp  A @link comparison_functors comparison functor@endlink.
1250    *  @return   A boolean true or false.
1251    *
1252    *  The same as the four-parameter @c lexicographical_compare, but uses the
1253    *  comp parameter instead of @c <.
1254   */
1255   template<typename _II1, typename _II2, typename _Compare>
1256     inline bool
1257     lexicographical_compare(_II1 __first1, _II1 __last1,
1258 			    _II2 __first2, _II2 __last2, _Compare __comp)
1259     {
1260       // concept requirements
1261       __glibcxx_function_requires(_InputIteratorConcept<_II1>)
1262       __glibcxx_function_requires(_InputIteratorConcept<_II2>)
1263       __glibcxx_requires_valid_range(__first1, __last1);
1264       __glibcxx_requires_valid_range(__first2, __last2);
1265 
1266       return std::__lexicographical_compare_impl
1267 	(__first1, __last1, __first2, __last2,
1268 	 __gnu_cxx::__ops::__iter_comp_iter(__comp));
1269     }
1270 
1271   template<typename _InputIterator1, typename _InputIterator2,
1272 	   typename _BinaryPredicate>
1273     pair<_InputIterator1, _InputIterator2>
1274     __mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1275 	       _InputIterator2 __first2, _BinaryPredicate __binary_pred)
1276     {
1277       while (__first1 != __last1 && __binary_pred(__first1, __first2))
1278 	{
1279 	  ++__first1;
1280 	  ++__first2;
1281 	}
1282       return pair<_InputIterator1, _InputIterator2>(__first1, __first2);
1283     }
1284 
1285   /**
1286    *  @brief Finds the places in ranges which don't match.
1287    *  @ingroup non_mutating_algorithms
1288    *  @param  __first1  An input iterator.
1289    *  @param  __last1   An input iterator.
1290    *  @param  __first2  An input iterator.
1291    *  @return   A pair of iterators pointing to the first mismatch.
1292    *
1293    *  This compares the elements of two ranges using @c == and returns a pair
1294    *  of iterators.  The first iterator points into the first range, the
1295    *  second iterator points into the second range, and the elements pointed
1296    *  to by the iterators are not equal.
1297   */
1298   template<typename _InputIterator1, typename _InputIterator2>
1299     inline pair<_InputIterator1, _InputIterator2>
1300     mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1301 	     _InputIterator2 __first2)
1302     {
1303       // concept requirements
1304       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
1305       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
1306       __glibcxx_function_requires(_EqualOpConcept<
1307 	    typename iterator_traits<_InputIterator1>::value_type,
1308 	    typename iterator_traits<_InputIterator2>::value_type>)
1309       __glibcxx_requires_valid_range(__first1, __last1);
1310 
1311       return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2,
1312 			     __gnu_cxx::__ops::__iter_equal_to_iter());
1313     }
1314 
1315   /**
1316    *  @brief Finds the places in ranges which don't match.
1317    *  @ingroup non_mutating_algorithms
1318    *  @param  __first1  An input iterator.
1319    *  @param  __last1   An input iterator.
1320    *  @param  __first2  An input iterator.
1321    *  @param __binary_pred A binary predicate @link functors
1322    *         functor@endlink.
1323    *  @return   A pair of iterators pointing to the first mismatch.
1324    *
1325    *  This compares the elements of two ranges using the binary_pred
1326    *  parameter, and returns a pair
1327    *  of iterators.  The first iterator points into the first range, the
1328    *  second iterator points into the second range, and the elements pointed
1329    *  to by the iterators are not equal.
1330   */
1331   template<typename _InputIterator1, typename _InputIterator2,
1332 	   typename _BinaryPredicate>
1333     inline pair<_InputIterator1, _InputIterator2>
1334     mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1335 	     _InputIterator2 __first2, _BinaryPredicate __binary_pred)
1336     {
1337       // concept requirements
1338       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
1339       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
1340       __glibcxx_requires_valid_range(__first1, __last1);
1341 
1342       return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2,
1343 	__gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
1344     }
1345 
1346 #if __cplusplus > 201103L
1347 
1348   template<typename _InputIterator1, typename _InputIterator2,
1349 	   typename _BinaryPredicate>
1350     pair<_InputIterator1, _InputIterator2>
1351     __mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1352 	       _InputIterator2 __first2, _InputIterator2 __last2,
1353 	       _BinaryPredicate __binary_pred)
1354     {
1355       while (__first1 != __last1 && __first2 != __last2
1356 	     && __binary_pred(__first1, __first2))
1357 	{
1358 	  ++__first1;
1359 	  ++__first2;
1360 	}
1361       return pair<_InputIterator1, _InputIterator2>(__first1, __first2);
1362     }
1363 
1364   /**
1365    *  @brief Finds the places in ranges which don't match.
1366    *  @ingroup non_mutating_algorithms
1367    *  @param  __first1  An input iterator.
1368    *  @param  __last1   An input iterator.
1369    *  @param  __first2  An input iterator.
1370    *  @param  __last2   An input iterator.
1371    *  @return   A pair of iterators pointing to the first mismatch.
1372    *
1373    *  This compares the elements of two ranges using @c == and returns a pair
1374    *  of iterators.  The first iterator points into the first range, the
1375    *  second iterator points into the second range, and the elements pointed
1376    *  to by the iterators are not equal.
1377   */
1378   template<typename _InputIterator1, typename _InputIterator2>
1379     inline pair<_InputIterator1, _InputIterator2>
1380     mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1381 	     _InputIterator2 __first2, _InputIterator2 __last2)
1382     {
1383       // concept requirements
1384       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
1385       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
1386       __glibcxx_function_requires(_EqualOpConcept<
1387 	    typename iterator_traits<_InputIterator1>::value_type,
1388 	    typename iterator_traits<_InputIterator2>::value_type>)
1389       __glibcxx_requires_valid_range(__first1, __last1);
1390       __glibcxx_requires_valid_range(__first2, __last2);
1391 
1392       return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2, __last2,
1393 			     __gnu_cxx::__ops::__iter_equal_to_iter());
1394     }
1395 
1396   /**
1397    *  @brief Finds the places in ranges which don't match.
1398    *  @ingroup non_mutating_algorithms
1399    *  @param  __first1  An input iterator.
1400    *  @param  __last1   An input iterator.
1401    *  @param  __first2  An input iterator.
1402    *  @param  __last2   An input iterator.
1403    *  @param __binary_pred A binary predicate @link functors
1404    *         functor@endlink.
1405    *  @return   A pair of iterators pointing to the first mismatch.
1406    *
1407    *  This compares the elements of two ranges using the binary_pred
1408    *  parameter, and returns a pair
1409    *  of iterators.  The first iterator points into the first range, the
1410    *  second iterator points into the second range, and the elements pointed
1411    *  to by the iterators are not equal.
1412   */
1413   template<typename _InputIterator1, typename _InputIterator2,
1414 	   typename _BinaryPredicate>
1415     inline pair<_InputIterator1, _InputIterator2>
1416     mismatch(_InputIterator1 __first1, _InputIterator1 __last1,
1417 	     _InputIterator2 __first2, _InputIterator2 __last2,
1418 	     _BinaryPredicate __binary_pred)
1419     {
1420       // concept requirements
1421       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator1>)
1422       __glibcxx_function_requires(_InputIteratorConcept<_InputIterator2>)
1423       __glibcxx_requires_valid_range(__first1, __last1);
1424       __glibcxx_requires_valid_range(__first2, __last2);
1425 
1426       return _GLIBCXX_STD_A::__mismatch(__first1, __last1, __first2, __last2,
1427 			     __gnu_cxx::__ops::__iter_comp_iter(__binary_pred));
1428     }
1429 #endif
1430 
1431 _GLIBCXX_END_NAMESPACE_ALGO
1432 _GLIBCXX_END_NAMESPACE_VERSION
1433 } // namespace std
1434 
1435 // NB: This file is included within many other C++ includes, as a way
1436 // of getting the base algorithms. So, make sure that parallel bits
1437 // come in too if requested.
1438 #ifdef _GLIBCXX_PARALLEL
1439 # include <parallel/algobase.h>
1440 #endif
1441 
1442 #endif
1443