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 <__iterator/distance.h> 16 #include <__iterator/iterator_traits.h> 17 #include <__random/uniform_int_distribution.h> 18 #include <type_traits> 19 20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) 21 # pragma GCC system_header 22 #endif 23 24 _LIBCPP_PUSH_MACROS 25 #include <__undef_macros> 26 27 _LIBCPP_BEGIN_NAMESPACE_STD 28 29 template <class _PopulationIterator, class _SampleIterator, class _Distance, 30 class _UniformRandomNumberGenerator> 31 _LIBCPP_INLINE_VISIBILITY 32 _SampleIterator __sample(_PopulationIterator __first, 33 _PopulationIterator __last, _SampleIterator __output_iter, 34 _Distance __n, 35 _UniformRandomNumberGenerator & __g, 36 input_iterator_tag) { 37 38 _Distance __k = 0; 39 for (; __first != __last && __k < __n; ++__first, (void) ++__k) 40 __output_iter[__k] = *__first; 41 _Distance __sz = __k; 42 for (; __first != __last; ++__first, (void) ++__k) { 43 _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g); 44 if (__r < __sz) 45 __output_iter[__r] = *__first; 46 } 47 return __output_iter + _VSTD::min(__n, __k); 48 } 49 50 template <class _PopulationIterator, class _SampleIterator, class _Distance, 51 class _UniformRandomNumberGenerator> 52 _LIBCPP_INLINE_VISIBILITY 53 _SampleIterator __sample(_PopulationIterator __first, 54 _PopulationIterator __last, _SampleIterator __output_iter, 55 _Distance __n, 56 _UniformRandomNumberGenerator& __g, 57 forward_iterator_tag) { 58 _Distance __unsampled_sz = _VSTD::distance(__first, __last); 59 for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) { 60 _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g); 61 if (__r < __n) { 62 *__output_iter++ = *__first; 63 --__n; 64 } 65 } 66 return __output_iter; 67 } 68 69 template <class _PopulationIterator, class _SampleIterator, class _Distance, 70 class _UniformRandomNumberGenerator> 71 _LIBCPP_INLINE_VISIBILITY 72 _SampleIterator __sample(_PopulationIterator __first, 73 _PopulationIterator __last, _SampleIterator __output_iter, 74 _Distance __n, _UniformRandomNumberGenerator& __g) { 75 typedef typename iterator_traits<_PopulationIterator>::iterator_category 76 _PopCategory; 77 typedef typename iterator_traits<_PopulationIterator>::difference_type 78 _Difference; 79 static_assert(__is_cpp17_forward_iterator<_PopulationIterator>::value || 80 __is_cpp17_random_access_iterator<_SampleIterator>::value, 81 "SampleIterator must meet the requirements of RandomAccessIterator"); 82 typedef typename common_type<_Distance, _Difference>::type _CommonType; 83 _LIBCPP_ASSERT(__n >= 0, "N must be a positive number."); 84 return _VSTD::__sample( 85 __first, __last, __output_iter, _CommonType(__n), 86 __g, _PopCategory()); 87 } 88 89 #if _LIBCPP_STD_VER > 14 90 template <class _PopulationIterator, class _SampleIterator, class _Distance, 91 class _UniformRandomNumberGenerator> 92 inline _LIBCPP_INLINE_VISIBILITY 93 _SampleIterator sample(_PopulationIterator __first, 94 _PopulationIterator __last, _SampleIterator __output_iter, 95 _Distance __n, _UniformRandomNumberGenerator&& __g) { 96 return _VSTD::__sample(__first, __last, __output_iter, __n, __g); 97 } 98 #endif // _LIBCPP_STD_VER > 14 99 100 _LIBCPP_END_NAMESPACE_STD 101 102 _LIBCPP_POP_MACROS 103 104 #endif // _LIBCPP___ALGORITHM_SAMPLE_H 105