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 <__assert> 14 #include <__config> 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 # pragma clang include_instead(<algorithm>) 21 #endif 22 23 _LIBCPP_PUSH_MACROS 24 #include <__undef_macros> 25 26 _LIBCPP_BEGIN_NAMESPACE_STD 27 28 template <class _PopulationIterator, class _SampleIterator, class _Distance, 29 class _UniformRandomNumberGenerator> 30 _LIBCPP_INLINE_VISIBILITY 31 _SampleIterator __sample(_PopulationIterator __first, 32 _PopulationIterator __last, _SampleIterator __output_iter, 33 _Distance __n, 34 _UniformRandomNumberGenerator & __g, 35 input_iterator_tag) { 36 37 _Distance __k = 0; 38 for (; __first != __last && __k < __n; ++__first, (void) ++__k) 39 __output_iter[__k] = *__first; 40 _Distance __sz = __k; 41 for (; __first != __last; ++__first, (void) ++__k) { 42 _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g); 43 if (__r < __sz) 44 __output_iter[__r] = *__first; 45 } 46 return __output_iter + _VSTD::min(__n, __k); 47 } 48 49 template <class _PopulationIterator, class _SampleIterator, class _Distance, 50 class _UniformRandomNumberGenerator> 51 _LIBCPP_INLINE_VISIBILITY 52 _SampleIterator __sample(_PopulationIterator __first, 53 _PopulationIterator __last, _SampleIterator __output_iter, 54 _Distance __n, 55 _UniformRandomNumberGenerator& __g, 56 forward_iterator_tag) { 57 _Distance __unsampled_sz = _VSTD::distance(__first, __last); 58 for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) { 59 _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g); 60 if (__r < __n) { 61 *__output_iter++ = *__first; 62 --__n; 63 } 64 } 65 return __output_iter; 66 } 67 68 template <class _PopulationIterator, class _SampleIterator, class _Distance, 69 class _UniformRandomNumberGenerator> 70 _LIBCPP_INLINE_VISIBILITY 71 _SampleIterator __sample(_PopulationIterator __first, 72 _PopulationIterator __last, _SampleIterator __output_iter, 73 _Distance __n, _UniformRandomNumberGenerator& __g) { 74 typedef typename iterator_traits<_PopulationIterator>::iterator_category 75 _PopCategory; 76 typedef typename iterator_traits<_PopulationIterator>::difference_type 77 _Difference; 78 static_assert(__is_cpp17_forward_iterator<_PopulationIterator>::value || 79 __is_cpp17_random_access_iterator<_SampleIterator>::value, 80 "SampleIterator must meet the requirements of RandomAccessIterator"); 81 typedef typename common_type<_Distance, _Difference>::type _CommonType; 82 _LIBCPP_ASSERT(__n >= 0, "N must be a positive number."); 83 return _VSTD::__sample( 84 __first, __last, __output_iter, _CommonType(__n), 85 __g, _PopCategory()); 86 } 87 88 #if _LIBCPP_STD_VER > 14 89 template <class _PopulationIterator, class _SampleIterator, class _Distance, 90 class _UniformRandomNumberGenerator> 91 inline _LIBCPP_INLINE_VISIBILITY 92 _SampleIterator sample(_PopulationIterator __first, 93 _PopulationIterator __last, _SampleIterator __output_iter, 94 _Distance __n, _UniformRandomNumberGenerator&& __g) { 95 return _VSTD::__sample(__first, __last, __output_iter, __n, __g); 96 } 97 #endif // _LIBCPP_STD_VER > 14 98 99 _LIBCPP_END_NAMESPACE_STD 100 101 _LIBCPP_POP_MACROS 102 103 #endif // _LIBCPP___ALGORITHM_SAMPLE_H 104