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 124