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, 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