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 <__utility/move.h> 20 #include <type_traits> 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(__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 > 14 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(__is_cpp17_forward_iterator<_PopulationIterator>::value || 99 __is_cpp17_random_access_iterator<_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 > 14 107 108 _LIBCPP_END_NAMESPACE_STD 109 110 _LIBCPP_POP_MACROS 111 112 #endif // _LIBCPP___ALGORITHM_SAMPLE_H 113