libcxx/include/__algorithm/sample.h

   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,
  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
  56 template <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
  80 template <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
 103 template <class _PopulationIterator, class _SampleIterator, class _Distance, class _UniformRandomNumberGenerator>
 104 inline _LIBCPP_HIDE_FROM_ABI _SampleIterator
 105 sample(_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