1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___ALGORITHM_SAMPLE_H
10 #define _LIBCPP___ALGORITHM_SAMPLE_H
11 
12 #include <__algorithm/iterator_operations.h>
13 #include <__algorithm/min.h>
14 #include <__assert>
15 #include <__config>
16 #include <__iterator/distance.h>
17 #include <__iterator/iterator_traits.h>
18 #include <__random/uniform_int_distribution.h>
19 #include <__type_traits/common_type.h>
20 #include <__utility/move.h>
21 
22 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
23 #  pragma GCC system_header
24 #endif
25 
26 _LIBCPP_PUSH_MACROS
27 #include <__undef_macros>
28 
29 _LIBCPP_BEGIN_NAMESPACE_STD
30 
31 template <class _AlgPolicy,
32           class _PopulationIterator, class _PopulationSentinel, class _SampleIterator, class _Distance,
33           class _UniformRandomNumberGenerator>
34 _LIBCPP_INLINE_VISIBILITY
35 _SampleIterator __sample(_PopulationIterator __first,
36                          _PopulationSentinel __last, _SampleIterator __output_iter,
37                          _Distance __n,
38                          _UniformRandomNumberGenerator& __g,
39                          input_iterator_tag) {
40 
41   _Distance __k = 0;
42   for (; __first != __last && __k < __n; ++__first, (void) ++__k)
43     __output_iter[__k] = *__first;
44   _Distance __sz = __k;
45   for (; __first != __last; ++__first, (void) ++__k) {
46     _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g);
47     if (__r < __sz)
48       __output_iter[__r] = *__first;
49   }
50   return __output_iter + _VSTD::min(__n, __k);
51 }
52 
53 template <class _AlgPolicy,
54           class _PopulationIterator, class _PopulationSentinel, class _SampleIterator, class _Distance,
55           class _UniformRandomNumberGenerator>
56 _LIBCPP_INLINE_VISIBILITY
57 _SampleIterator __sample(_PopulationIterator __first,
58                          _PopulationSentinel __last, _SampleIterator __output_iter,
59                          _Distance __n,
60                          _UniformRandomNumberGenerator& __g,
61                          forward_iterator_tag) {
62   _Distance __unsampled_sz = _IterOps<_AlgPolicy>::distance(__first, __last);
63   for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) {
64     _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
65     if (__r < __n) {
66       *__output_iter++ = *__first;
67       --__n;
68     }
69   }
70   return __output_iter;
71 }
72 
73 template <class _AlgPolicy,
74           class _PopulationIterator, class _PopulationSentinel, class _SampleIterator, class _Distance,
75           class _UniformRandomNumberGenerator>
76 _LIBCPP_INLINE_VISIBILITY
77 _SampleIterator __sample(_PopulationIterator __first,
78                          _PopulationSentinel __last, _SampleIterator __output_iter,
79                          _Distance __n, _UniformRandomNumberGenerator& __g) {
80   _LIBCPP_ASSERT_UNCATEGORIZED(__n >= 0, "N must be a positive number.");
81 
82   using _PopIterCategory = typename _IterOps<_AlgPolicy>::template __iterator_category<_PopulationIterator>;
83   using _Difference = typename _IterOps<_AlgPolicy>::template __difference_type<_PopulationIterator>;
84   using _CommonType = typename common_type<_Distance, _Difference>::type;
85 
86   return std::__sample<_AlgPolicy>(
87       std::move(__first), std::move(__last), std::move(__output_iter), _CommonType(__n),
88       __g, _PopIterCategory());
89 }
90 
91 #if _LIBCPP_STD_VER >= 17
92 template <class _PopulationIterator, class _SampleIterator, class _Distance,
93           class _UniformRandomNumberGenerator>
94 inline _LIBCPP_INLINE_VISIBILITY
95 _SampleIterator sample(_PopulationIterator __first,
96                        _PopulationIterator __last, _SampleIterator __output_iter,
97                        _Distance __n, _UniformRandomNumberGenerator&& __g) {
98   static_assert(__has_forward_iterator_category<_PopulationIterator>::value ||
99                 __has_random_access_iterator_category<_SampleIterator>::value,
100                 "SampleIterator must meet the requirements of RandomAccessIterator");
101 
102   return std::__sample<_ClassicAlgPolicy>(
103       std::move(__first), std::move(__last), std::move(__output_iter), __n, __g);
104 }
105 
106 #endif // _LIBCPP_STD_VER >= 17
107 
108 _LIBCPP_END_NAMESPACE_STD
109 
110 _LIBCPP_POP_MACROS
111 
112 #endif // _LIBCPP___ALGORITHM_SAMPLE_H
113