xref: /freebsd/contrib/llvm-project/libcxx/include/__algorithm/sample.h (revision 3e8eb5c7f4909209c042403ddee340b2ee7003a5)
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 <__config>
14 #include <__debug>
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 #endif
21 
22 _LIBCPP_PUSH_MACROS
23 #include <__undef_macros>
24 
25 _LIBCPP_BEGIN_NAMESPACE_STD
26 
27 template <class _PopulationIterator, class _SampleIterator, class _Distance,
28           class _UniformRandomNumberGenerator>
29 _LIBCPP_INLINE_VISIBILITY
30 _SampleIterator __sample(_PopulationIterator __first,
31                          _PopulationIterator __last, _SampleIterator __output_iter,
32                          _Distance __n,
33                          _UniformRandomNumberGenerator & __g,
34                          input_iterator_tag) {
35 
36   _Distance __k = 0;
37   for (; __first != __last && __k < __n; ++__first, (void) ++__k)
38     __output_iter[__k] = *__first;
39   _Distance __sz = __k;
40   for (; __first != __last; ++__first, (void) ++__k) {
41     _Distance __r = uniform_int_distribution<_Distance>(0, __k)(__g);
42     if (__r < __sz)
43       __output_iter[__r] = *__first;
44   }
45   return __output_iter + _VSTD::min(__n, __k);
46 }
47 
48 template <class _PopulationIterator, class _SampleIterator, class _Distance,
49           class _UniformRandomNumberGenerator>
50 _LIBCPP_INLINE_VISIBILITY
51 _SampleIterator __sample(_PopulationIterator __first,
52                          _PopulationIterator __last, _SampleIterator __output_iter,
53                          _Distance __n,
54                          _UniformRandomNumberGenerator& __g,
55                          forward_iterator_tag) {
56   _Distance __unsampled_sz = _VSTD::distance(__first, __last);
57   for (__n = _VSTD::min(__n, __unsampled_sz); __n != 0; ++__first) {
58     _Distance __r = uniform_int_distribution<_Distance>(0, --__unsampled_sz)(__g);
59     if (__r < __n) {
60       *__output_iter++ = *__first;
61       --__n;
62     }
63   }
64   return __output_iter;
65 }
66 
67 template <class _PopulationIterator, class _SampleIterator, class _Distance,
68           class _UniformRandomNumberGenerator>
69 _LIBCPP_INLINE_VISIBILITY
70 _SampleIterator __sample(_PopulationIterator __first,
71                          _PopulationIterator __last, _SampleIterator __output_iter,
72                          _Distance __n, _UniformRandomNumberGenerator& __g) {
73   typedef typename iterator_traits<_PopulationIterator>::iterator_category
74         _PopCategory;
75   typedef typename iterator_traits<_PopulationIterator>::difference_type
76         _Difference;
77   static_assert(__is_cpp17_forward_iterator<_PopulationIterator>::value ||
78                 __is_cpp17_random_access_iterator<_SampleIterator>::value,
79                 "SampleIterator must meet the requirements of RandomAccessIterator");
80   typedef typename common_type<_Distance, _Difference>::type _CommonType;
81   _LIBCPP_ASSERT(__n >= 0, "N must be a positive number.");
82   return _VSTD::__sample(
83       __first, __last, __output_iter, _CommonType(__n),
84       __g, _PopCategory());
85 }
86 
87 #if _LIBCPP_STD_VER > 14
88 template <class _PopulationIterator, class _SampleIterator, class _Distance,
89           class _UniformRandomNumberGenerator>
90 inline _LIBCPP_INLINE_VISIBILITY
91 _SampleIterator sample(_PopulationIterator __first,
92                        _PopulationIterator __last, _SampleIterator __output_iter,
93                        _Distance __n, _UniformRandomNumberGenerator&& __g) {
94     return _VSTD::__sample(__first, __last, __output_iter, __n, __g);
95 }
96 #endif // _LIBCPP_STD_VER > 14
97 
98 _LIBCPP_END_NAMESPACE_STD
99 
100 _LIBCPP_POP_MACROS
101 
102 #endif // _LIBCPP___ALGORITHM_SAMPLE_H
103