contrib/llvm-project/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/min.h>
  13 #include <__config>
  14 #include <__debug>
  15 #include <__random/uniform_int_distribution.h>
  16 #include <iterator>
  17
  18 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  19 #pragma GCC system_header
  20 #endif
  21
  22 _LIBCPP_PUSH_MACROS
  23 #include <__undef_macros>
  24
  25 _LIBCPP_BEGIN_NAMESPACE_STD
  26
  27 template <class _PopulationIterator, class _SampleIterator, class _Distance,
  28           class _UniformRandomNumberGenerator>
  29 _LIBCPP_INLINE_VISIBILITY
  30 _SampleIterator __sample(_PopulationIterator __first,
  31                          _PopulationIterator __last, _SampleIterator __output_iter,
  32                          _Distance __n,
  33                          _UniformRandomNumberGenerator & __g,
  34                          input_iterator_tag) {
  35
  36   _Distance __k = 0;
  37   for (; __first != __last && __k < __n; ++__first, (void) ++__k)
  38     __output_iter[__k] = *__first;
  39   _Distance __sz = __k;
  40   for (; __first != __last; ++__first, (void) ++__k) {
  41     _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g);
  42     if (__r < __sz)
  43       __output_iter[__r] = *__first;
  44   }
  45   return __output_iter + _VSTD::min(__n, __k);
  46 }
  47
  48 template <class _PopulationIterator, class _SampleIterator, class _Distance,
  49           class _UniformRandomNumberGenerator>
  50 _LIBCPP_INLINE_VISIBILITY
  51 _SampleIterator __sample(_PopulationIterator __first,
  52                          _PopulationIterator __last, _SampleIterator __output_iter,
  53                          _Distance __n,
  54                          _UniformRandomNumberGenerator& __g,
  55                          forward_iterator_tag) {
  56   _Distance __unsampled_sz = _VSTD::distance(__first, __last);
  57   for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) {
  58     _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
  59     if (__r < __n) {
  60       *__output_iter++ = *__first;
  61       --__n;
  62     }
  63   }
  64   return __output_iter;
  65 }
  66
  67 template <class _PopulationIterator, class _SampleIterator, class _Distance,
  68           class _UniformRandomNumberGenerator>
  69 _LIBCPP_INLINE_VISIBILITY
  70 _SampleIterator __sample(_PopulationIterator __first,
  71                          _PopulationIterator __last, _SampleIterator __output_iter,
  72                          _Distance __n, _UniformRandomNumberGenerator& __g) {
  73   typedef typename iterator_traits<_PopulationIterator>::iterator_category
  74         _PopCategory;
  75   typedef typename iterator_traits<_PopulationIterator>::difference_type
  76         _Difference;
  77   static_assert(__is_cpp17_forward_iterator<_PopulationIterator>::value ||
  78                 __is_cpp17_random_access_iterator<_SampleIterator>::value,
  79                 "SampleIterator must meet the requirements of RandomAccessIterator");
  80   typedef typename common_type<_Distance, _Difference>::type _CommonType;
  81   _LIBCPP_ASSERT(__n >= 0, "N must be a positive number.");
  82   return _VSTD::__sample(
  83       __first, __last, __output_iter, _CommonType(__n),
  84       __g, _PopCategory());
  85 }
  86
  87 #if _LIBCPP_STD_VER > 14
  88 template <class _PopulationIterator, class _SampleIterator, class _Distance,
  89           class _UniformRandomNumberGenerator>
  90 inline _LIBCPP_INLINE_VISIBILITY
  91 _SampleIterator sample(_PopulationIterator __first,
  92                        _PopulationIterator __last, _SampleIterator __output_iter,
  93                        _Distance __n, _UniformRandomNumberGenerator&& __g) {
  94     return _VSTD::__sample(__first, __last, __output_iter, __n, __g);
  95 }
  96 #endif // _LIBCPP_STD_VER > 14
  97
  98 _LIBCPP_END_NAMESPACE_STD
  99
 100 _LIBCPP_POP_MACROS
 101
 102 #endif // _LIBCPP___ALGORITHM_SAMPLE_H