libstdc++-v3/include/experimental/algorithm

   1 // <experimental/algorithm> -*- C++ -*-
   2
   3 // Copyright (C) 2014-2016 Free Software Foundation, Inc.
   4 //
   5 // This file is part of the GNU ISO C++ Library.  This library is free
   6 // software; you can redistribute it and/or modify it under the
   7 // terms of the GNU General Public License as published by the
   8 // Free Software Foundation; either version 3, or (at your option)
   9 // any later version.
  10
  11 // This library is distributed in the hope that it will be useful,
  12 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 // GNU General Public License for more details.
  15
  16 // Under Section 7 of GPL version 3, you are granted additional
  17 // permissions described in the GCC Runtime Library Exception, version
  18 // 3.1, as published by the Free Software Foundation.
  19
  20 // You should have received a copy of the GNU General Public License and
  21 // a copy of the GCC Runtime Library Exception along with this program;
  22 // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
  23 // <http://www.gnu.org/licenses/>.
  24
  25 /** @file experimental/algorithm
  26  *  This is a TS C++ Library header.
  27  */
  28
  29 #ifndef _GLIBCXX_EXPERIMENTAL_ALGORITHM
  30 #define _GLIBCXX_EXPERIMENTAL_ALGORITHM 1
  31
  32 #pragma GCC system_header
  33
  34 #if __cplusplus <= 201103L
  35 # include <bits/c++14_warning.h>
  36 #else
  37
  38 #include <algorithm>
  39 #include <random>
  40
  41 namespace std _GLIBCXX_VISIBILITY(default)
  42 {
  43 namespace experimental
  44 {
  45 inline namespace fundamentals_v1
  46 {
  47 _GLIBCXX_BEGIN_NAMESPACE_VERSION
  48
  49   template<typename _ForwardIterator, typename _Searcher>
  50     inline _ForwardIterator
  51     search(_ForwardIterator __first, _ForwardIterator __last,
  52            const _Searcher& __searcher)
  53     { return __searcher(__first, __last); }
  54
  55 #define __cpp_lib_experimental_sample 201402
  56
  57   /// Reservoir sampling algorithm.
  58   template<typename _InputIterator, typename _RandomAccessIterator,
  59            typename _Size, typename _UniformRandomNumberGenerator>
  60     _RandomAccessIterator
  61     __sample(_InputIterator __first, _InputIterator __last, input_iterator_tag,
  62              _RandomAccessIterator __out, random_access_iterator_tag,
  63              _Size __n, _UniformRandomNumberGenerator&& __g)
  64     {
  65       using __distrib_type = std::uniform_int_distribution<_Size>;
  66       using __param_type = typename __distrib_type::param_type;
  67       __distrib_type __d{};
  68       _Size __sample_sz = 0;
  69       while (__first != __last && __sample_sz != __n)
  70         __out[__sample_sz++] = *__first++;
  71       for (auto __pop_sz = __sample_sz; __first != __last;
  72           ++__first, ++__pop_sz)
  73         {
  74           const auto __k = __d(__g, __param_type{0, __pop_sz});
  75           if (__k < __n)
  76             __out[__k] = *__first;
  77         }
  78       return __out + __sample_sz;
  79     }
  80
  81   /// Selection sampling algorithm.
  82   template<typename _ForwardIterator, typename _OutputIterator, typename _Cat,
  83            typename _Size, typename _UniformRandomNumberGenerator>
  84     _OutputIterator
  85     __sample(_ForwardIterator __first, _ForwardIterator __last,
  86              forward_iterator_tag,
  87              _OutputIterator __out, _Cat,
  88              _Size __n, _UniformRandomNumberGenerator&& __g)
  89     {
  90       using __distrib_type = std::uniform_int_distribution<_Size>;
  91       using __param_type = typename __distrib_type::param_type;
  92       __distrib_type __d{};
  93       _Size __unsampled_sz = std::distance(__first, __last);
  94       for (__n = std::min(__n, __unsampled_sz); __n != 0; ++__first)
  95         if (__d(__g, __param_type{0, --__unsampled_sz}) < __n)
  96           {
  97             *__out++ = *__first;
  98             --__n;
  99           }
 100       return __out;
 101     }
 102
 103   /// Take a random sample from a population.
 104   template<typename _PopulationIterator, typename _SampleIterator,
 105            typename _Distance, typename _UniformRandomNumberGenerator>
 106     _SampleIterator
 107     sample(_PopulationIterator __first, _PopulationIterator __last,
 108            _SampleIterator __out, _Distance __n,
 109            _UniformRandomNumberGenerator&& __g)
 110     {
 111       using __pop_cat = typename
 112         std::iterator_traits<_PopulationIterator>::iterator_category;
 113       using __samp_cat = typename
 114         std::iterator_traits<_SampleIterator>::iterator_category;
 115
 116       static_assert(
 117           __or_<is_convertible<__pop_cat, forward_iterator_tag>,
 118                 is_convertible<__samp_cat, random_access_iterator_tag>>::value,
 119           "output range must use a RandomAccessIterator when input range"
 120           " does not meet the ForwardIterator requirements");
 121
 122       static_assert(is_integral<_Distance>::value,
 123                     "sample size must be an integer type");
 124
 125       return std::experimental::__sample(
 126           __first, __last, __pop_cat{}, __out, __samp_cat{},
 127           __n, std::forward<_UniformRandomNumberGenerator>(__g));
 128     }
 129
 130 _GLIBCXX_END_NAMESPACE_VERSION
 131 } // namespace fundamentals_v1
 132 } // namespace experimental
 133 } // namespace std
 134
 135 #endif // C++14
 136
 137 #endif // _GLIBCXX_EXPERIMENTAL_ALGORITHM