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