libstdc++
quicksort.h
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24
25/** @file parallel/quicksort.h
26 * @brief Implementation of a unbalanced parallel quicksort (in-place).
27 * This file is a GNU parallel extension to the Standard C++ Library.
28 */
29
30// Written by Johannes Singler.
31
32#ifndef _GLIBCXX_PARALLEL_QUICKSORT_H
33#define _GLIBCXX_PARALLEL_QUICKSORT_H 1
34
35#include <parallel/parallel.h>
36#include <parallel/partition.h>
37
38namespace __gnu_parallel
39{
40 /** @brief Unbalanced quicksort divide step.
41 * @param __begin Begin iterator of subsequence.
42 * @param __end End iterator of subsequence.
43 * @param __comp Comparator.
44 * @param __pivot_rank Desired __rank of the pivot.
45 * @param __num_samples Choose pivot from that many samples.
46 * @param __num_threads Number of threads that are allowed to work on
47 * this part.
48 */
49 template<typename _RAIter, typename _Compare>
51 __parallel_sort_qs_divide(_RAIter __begin, _RAIter __end,
52 _Compare __comp, typename std::iterator_traits
53 <_RAIter>::difference_type __pivot_rank,
55 <_RAIter>::difference_type
56 __num_samples, _ThreadIndex __num_threads)
57 {
58 typedef std::iterator_traits<_RAIter> _TraitsType;
59 typedef typename _TraitsType::value_type _ValueType;
60 typedef typename _TraitsType::difference_type _DifferenceType;
61
62 _DifferenceType __n = __end - __begin;
63 __num_samples = std::min(__num_samples, __n);
64
65 // Allocate uninitialized, to avoid default constructor.
66 _ValueType* __samples = static_cast<_ValueType*>
67 (::operator new(__num_samples * sizeof(_ValueType)));
68
69 for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
70 {
71 const unsigned long long __index = static_cast<unsigned long long>
72 (__s) * __n / __num_samples;
73 ::new(&(__samples[__s])) _ValueType(__begin[__index]);
74 }
75
76 __gnu_sequential::sort(__samples, __samples + __num_samples, __comp);
77
78 _ValueType& __pivot = __samples[__pivot_rank * __num_samples / __n];
79
81 __pred(__comp, __pivot);
82 _DifferenceType __split = __parallel_partition(__begin, __end,
83 __pred, __num_threads);
84
85 for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
86 __samples[__s].~_ValueType();
87 ::operator delete(__samples);
88
89 return __split;
90 }
91
92 /** @brief Unbalanced quicksort conquer step.
93 * @param __begin Begin iterator of subsequence.
94 * @param __end End iterator of subsequence.
95 * @param __comp Comparator.
96 * @param __num_threads Number of threads that are allowed to work on
97 * this part.
98 */
99 template<typename _RAIter, typename _Compare>
100 void
101 __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end,
102 _Compare __comp,
103 _ThreadIndex __num_threads)
104 {
105 typedef std::iterator_traits<_RAIter> _TraitsType;
106 typedef typename _TraitsType::value_type _ValueType;
107 typedef typename _TraitsType::difference_type _DifferenceType;
108
109 if (__num_threads <= 1)
110 {
111 __gnu_sequential::sort(__begin, __end, __comp);
112 return;
113 }
114
115 _DifferenceType __n = __end - __begin, __pivot_rank;
116
117 if (__n <= 1)
118 return;
119
120 _ThreadIndex __num_threads_left;
121
122 if ((__num_threads % 2) == 1)
123 __num_threads_left = __num_threads / 2 + 1;
124 else
125 __num_threads_left = __num_threads / 2;
126
127 __pivot_rank = __n * __num_threads_left / __num_threads;
128
129 _DifferenceType __split = __parallel_sort_qs_divide
130 (__begin, __end, __comp, __pivot_rank,
131 _Settings::get().sort_qs_num_samples_preset, __num_threads);
132
133#pragma omp parallel sections num_threads(2)
134 {
135#pragma omp section
136 __parallel_sort_qs_conquer(__begin, __begin + __split,
137 __comp, __num_threads_left);
138#pragma omp section
139 __parallel_sort_qs_conquer(__begin + __split, __end,
140 __comp, __num_threads - __num_threads_left);
141 }
142 }
143
144
145 /** @brief Unbalanced quicksort main call.
146 * @param __begin Begin iterator of input sequence.
147 * @param __end End iterator input sequence, ignored.
148 * @param __comp Comparator.
149 * @param __num_threads Number of threads that are allowed to work on
150 * this part.
151 */
152 template<typename _RAIter, typename _Compare>
153 void
154 __parallel_sort_qs(_RAIter __begin, _RAIter __end,
155 _Compare __comp,
156 _ThreadIndex __num_threads)
157 {
158 _GLIBCXX_CALL(__n)
159
160 typedef std::iterator_traits<_RAIter> _TraitsType;
161 typedef typename _TraitsType::value_type _ValueType;
162 typedef typename _TraitsType::difference_type _DifferenceType;
163
164 _DifferenceType __n = __end - __begin;
165
166 // At least one element per processor.
167 if (__num_threads > __n)
168 __num_threads = static_cast<_ThreadIndex>(__n);
169
171 __begin, __begin + __n, __comp, __num_threads);
172 }
173
174} //namespace __gnu_parallel
175
176#endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */
Parallel implementation of std::partition(), std::nth_element(), and std::partial_sort()....
End-user include file. Provides advanced settings and tuning options. This file is a GNU parallel ext...
#define _GLIBCXX_CALL(__n)
Macro to produce log message when entering a function.
constexpr const _Tp & min(const _Tp &, const _Tp &)
This does what you think it does.
Definition: stl_algobase.h:230
GNU parallel code for public use.
uint16_t _ThreadIndex
Unsigned integer to index a thread number. The maximum thread number (for each processor) must fit in...
Definition: types.h:123
void __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads)
Unbalanced quicksort conquer step.
Definition: quicksort.h:101
std::iterator_traits< _RAIter >::difference_type __parallel_sort_qs_divide(_RAIter __begin, _RAIter __end, _Compare __comp, typename std::iterator_traits< _RAIter >::difference_type __pivot_rank, typename std::iterator_traits< _RAIter >::difference_type __num_samples, _ThreadIndex __num_threads)
Unbalanced quicksort divide step.
Definition: quicksort.h:51
void __parallel_sort_qs(_RAIter __begin, _RAIter __end, _Compare __comp, _ThreadIndex __num_threads)
Unbalanced quicksort main call.
Definition: quicksort.h:154
std::iterator_traits< _RAIter >::difference_type __parallel_partition(_RAIter __begin, _RAIter __end, _Predicate __pred, _ThreadIndex __num_threads)
Parallel implementation of std::partition.
Definition: partition.h:56
Traits class for iterators.
Similar to std::binder2nd, but giving the argument types explicitly.
Definition: base.h:222
static const _Settings & get()
Get the global settings.