v1/__algorithm/sample.h

0001 //===----------------------------------------------------------------------===//
0002 //
0003 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
0004 // See https://llvm.org/LICENSE.txt for license information.
0005 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
0006 //
0007 //===----------------------------------------------------------------------===//
0008
0009 #ifndef _LIBCPP___ALGORITHM_SAMPLE_H
0010 #define _LIBCPP___ALGORITHM_SAMPLE_H
0011
0012 #include <__algorithm/iterator_operations.h>
0013 #include <__algorithm/min.h>
0014 #include <__assert>
0015 #include <__config>
0016 #include <__iterator/distance.h>
0017 #include <__iterator/iterator_traits.h>
0018 #include <__random/uniform_int_distribution.h>
0019 #include <__type_traits/common_type.h>
0020 #include <__utility/move.h>
0021
0022 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
0023 #  pragma GCC system_header
0024 #endif
0025
0026 _LIBCPP_PUSH_MACROS
0027 #include <__undef_macros>
0028
0029 _LIBCPP_BEGIN_NAMESPACE_STD
0030
0031 template <class _AlgPolicy,
0032           class _PopulationIterator,
0033           class _PopulationSentinel,
0034           class _SampleIterator,
0035           class _Distance,
0036           class _UniformRandomNumberGenerator>
0037 _LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
0038     _PopulationIterator __first,
0039     _PopulationSentinel __last,
0040     _SampleIterator __output_iter,
0041     _Distance __n,
0042     _UniformRandomNumberGenerator& __g,
0043     input_iterator_tag) {
0044   _Distance __k = 0;
0045   for (; __first != __last && __k < __n; ++__first, (void)++__k)
0046     __output_iter[__k] = *__first;
0047   _Distance __sz = __k;
0048   for (; __first != __last; ++__first, (void)++__k) {
0049     _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g);
0050     if (__r < __sz)
0051       __output_iter[__r] = *__first;
0052   }
0053   return __output_iter + std::min(__n, __k);
0054 }
0055
0056 template <class _AlgPolicy,
0057           class _PopulationIterator,
0058           class _PopulationSentinel,
0059           class _SampleIterator,
0060           class _Distance,
0061           class _UniformRandomNumberGenerator>
0062 _LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
0063     _PopulationIterator __first,
0064     _PopulationSentinel __last,
0065     _SampleIterator __output_iter,
0066     _Distance __n,
0067     _UniformRandomNumberGenerator& __g,
0068     forward_iterator_tag) {
0069   _Distance __unsampled_sz = _IterOps<_AlgPolicy>::distance(__first, __last);
0070   for (__n = std::min(__n, __unsampled_sz); __n != 0; ++__first) {
0071     _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
0072     if (__r < __n) {
0073       *__output_iter++ = *__first;
0074       --__n;
0075     }
0076   }
0077   return __output_iter;
0078 }
0079
0080 template <class _AlgPolicy,
0081           class _PopulationIterator,
0082           class _PopulationSentinel,
0083           class _SampleIterator,
0084           class _Distance,
0085           class _UniformRandomNumberGenerator>
0086 _LIBCPP_HIDE_FROM_ABI _SampleIterator __sample(
0087     _PopulationIterator __first,
0088     _PopulationSentinel __last,
0089     _SampleIterator __output_iter,
0090     _Distance __n,
0091     _UniformRandomNumberGenerator& __g) {
0092   _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(__n >= 0, "N must be a positive number.");
0093
0094   using _PopIterCategory = typename _IterOps<_AlgPolicy>::template __iterator_category<_PopulationIterator>;
0095   using _Difference      = typename _IterOps<_AlgPolicy>::template __difference_type<_PopulationIterator>;
0096   using _CommonType      = typename common_type<_Distance, _Difference>::type;
0097
0098   return std::__sample<_AlgPolicy>(
0099       std::move(__first), std::move(__last), std::move(__output_iter), _CommonType(__n), __g, _PopIterCategory());
0100 }
0101
0102 #if _LIBCPP_STD_VER >= 17
0103 template <class _PopulationIterator, class _SampleIterator, class _Distance, class _UniformRandomNumberGenerator>
0104 inline _LIBCPP_HIDE_FROM_ABI _SampleIterator
0105 sample(_PopulationIterator __first,
0106        _PopulationIterator __last,
0107        _SampleIterator __output_iter,
0108        _Distance __n,
0109        _UniformRandomNumberGenerator&& __g) {
0110   static_assert(__has_forward_iterator_category<_PopulationIterator>::value ||
0111                     __has_random_access_iterator_category<_SampleIterator>::value,
0112                 "SampleIterator must meet the requirements of RandomAccessIterator");
0113
0114   return std::__sample<_ClassicAlgPolicy>(std::move(__first), std::move(__last), std::move(__output_iter), __n, __g);
0115 }
0116
0117 #endif // _LIBCPP_STD_VER >= 17
0118
0119 _LIBCPP_END_NAMESPACE_STD
0120
0121 _LIBCPP_POP_MACROS
0122
0123 #endif // _LIBCPP___ALGORITHM_SAMPLE_H