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
31template <class _AlgPolicy,
32          class _PopulationIterator,
33          class _PopulationSentinel,
34          class _SampleIterator,
35          class _Distance,
36          class _UniformRandomNumberGenerator>
37_LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
38    _PopulationIterator __first,
39    _PopulationSentinel __last,
40    _SampleIterator __output_iter,
41    _Distance __n,
42    _UniformRandomNumberGenerator& __g,
43    input_iterator_tag) {
44  _Distance __k = 0;
45  for (; __first != __last && __k < __n; ++__first, (void)++__k)
46    __output_iter[__k] = *__first;
47  _Distance __sz = __k;
48  for (; __first != __last; ++__first, (void)++__k) {
49    _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g);
50    if (__r < __sz)
51      __output_iter[__r] = *__first;
52  }
53  return __output_iter + std::min(__n, __k);
54}
55
56template <class _AlgPolicy,
57          class _PopulationIterator,
58          class _PopulationSentinel,
59          class _SampleIterator,
60          class _Distance,
61          class _UniformRandomNumberGenerator>
62_LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
63    _PopulationIterator __first,
64    _PopulationSentinel __last,
65    _SampleIterator __output_iter,
66    _Distance __n,
67    _UniformRandomNumberGenerator& __g,
68    forward_iterator_tag) {
69  _Distance __unsampled_sz = _IterOps<_AlgPolicy>::distance(__first, __last);
70  for (__n = std::min(__n, __unsampled_sz); __n != 0; ++__first) {
71    _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
72    if (__r < __n) {
73      *__output_iter++ = *__first;
74      --__n;
75    }
76  }
77  return __output_iter;
78}
79
80template <class _AlgPolicy,
81          class _PopulationIterator,
82          class _PopulationSentinel,
83          class _SampleIterator,
84          class _Distance,
85          class _UniformRandomNumberGenerator>
86_LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
87    _PopulationIterator __first,
88    _PopulationSentinel __last,
89    _SampleIterator __output_iter,
90    _Distance __n,
91    _UniformRandomNumberGenerator& __g) {
92  _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "N must be a positive number.");
93
94  using _PopIterCategory = typename _IterOps<_AlgPolicy>::template __iterator_category<_PopulationIterator>;
95  using _Difference      = typename _IterOps<_AlgPolicy>::template __difference_type<_PopulationIterator>;
96  using _CommonType      = typename common_type<_Distance, _Difference>::type;
97
98  return std::__sample<_AlgPolicy>(
99      std::move(__first), std::move(__last), std::move(__output_iter), _CommonType(__n), __g, _PopIterCategory());
100}
101
102#if _LIBCPP_STD_VER >= 17
103template <class _PopulationIterator, class _SampleIterator, class _Distance, class _UniformRandomNumberGenerator>
104inline _LIBCPP_HIDE_FROM_ABI _SampleIterator
105sample(_PopulationIterator __first,
106       _PopulationIterator __last,
107       _SampleIterator __output_iter,
108       _Distance __n,
109       _UniformRandomNumberGenerator&& __g) {
110  static_assert(__has_forward_iterator_category<_PopulationIterator>::value ||
111                    __has_random_access_iterator_category<_SampleIterator>::value,
112                "SampleIterator must meet the requirements of RandomAccessIterator");
113
114  return std::__sample<_ClassicAlgPolicy>(std::move(__first), std::move(__last), std::move(__output_iter), __n, __g);
115}
116
117#endif // _LIBCPP_STD_VER >= 17
118
119_LIBCPP_END_NAMESPACE_STD
120
121_LIBCPP_POP_MACROS
122
123#endif // _LIBCPP___ALGORITHM_SAMPLE_H
124