3 // Copyright (C) 2007, 2008 Free Software Foundation, Inc.
5 // This file is part of the GNU ISO C++ Library. This library is free
6 // software; you can redistribute it and/or modify it under the terms
7 // of the GNU General Public License as published by the Free Software
8 // Foundation; either version 2, or (at your option) any later
11 // This library is distributed in the hope that it will be useful, but
12 // WITHOUT ANY WARRANTY; without even the implied warranty of
13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 // General Public License for more details.
16 // You should have received a copy of the GNU General Public License
17 // along with this library; see the file COPYING. If not, write to
18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
19 // MA 02111-1307, USA.
21 // As a special exception, you may use this file as part of a free
22 // software library without restriction. Specifically, if other files
23 // instantiate templates or use macros or inline functions from this
24 // file, or you compile this file and link it with other files to
25 // produce an executable, this file does not by itself cause the
26 // resulting executable to be covered by the GNU General Public
27 // License. This exception does not however invalidate any other
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31 /** @file parallel/quicksort.h
32 * @brief Implementation of a unbalanced parallel quicksort (in-place).
33 * This file is a GNU parallel extension to the Standard C++ Library.
36 // Written by Johannes Singler.
38 #ifndef _GLIBCXX_PARALLEL_QUICKSORT_H
39 #define _GLIBCXX_PARALLEL_QUICKSORT_H 1
41 #include <parallel/parallel.h>
42 #include <parallel/partition.h>
44 namespace __gnu_parallel
46 /** @brief Unbalanced quicksort divide step.
47 * @param begin Begin iterator of subsequence.
48 * @param end End iterator of subsequence.
49 * @param comp Comparator.
50 * @param pivot_rank Desired rank of the pivot.
51 * @param num_samples Choose pivot from that many samples.
52 * @param num_threads Number of threads that are allowed to work on
55 template<typename RandomAccessIterator, typename Comparator>
56 typename std::iterator_traits<RandomAccessIterator>::difference_type
57 parallel_sort_qs_divide(RandomAccessIterator begin,
58 RandomAccessIterator end,
59 Comparator comp, typename std::iterator_traits
60 <RandomAccessIterator>::difference_type pivot_rank,
61 typename std::iterator_traits
62 <RandomAccessIterator>::difference_type
63 num_samples, thread_index_t num_threads)
65 typedef std::iterator_traits<RandomAccessIterator> traits_type;
66 typedef typename traits_type::value_type value_type;
67 typedef typename traits_type::difference_type difference_type;
69 difference_type n = end - begin;
70 num_samples = std::min(num_samples, n);
72 // Allocate uninitialized, to avoid default constructor.
74 static_cast<value_type*>(::operator new(num_samples
75 * sizeof(value_type)));
77 for (difference_type s = 0; s < num_samples; ++s)
79 const unsigned long long index = static_cast<unsigned long long>(s)
81 ::new(&(samples[s])) value_type(begin[index]);
84 __gnu_sequential::sort(samples, samples + num_samples, comp);
86 value_type& pivot = samples[pivot_rank * num_samples / n];
88 __gnu_parallel::binder2nd<Comparator, value_type, value_type, bool>
90 difference_type split = parallel_partition(begin, end, pred, num_threads);
92 ::operator delete(samples);
97 /** @brief Unbalanced quicksort conquer step.
98 * @param begin Begin iterator of subsequence.
99 * @param end End iterator of subsequence.
100 * @param comp Comparator.
101 * @param num_threads Number of threads that are allowed to work on
104 template<typename RandomAccessIterator, typename Comparator>
106 parallel_sort_qs_conquer(RandomAccessIterator begin,
107 RandomAccessIterator end,
109 thread_index_t num_threads)
111 typedef std::iterator_traits<RandomAccessIterator> traits_type;
112 typedef typename traits_type::value_type value_type;
113 typedef typename traits_type::difference_type difference_type;
115 if (num_threads <= 1)
117 __gnu_sequential::sort(begin, end, comp);
121 difference_type n = end - begin, pivot_rank;
126 thread_index_t num_threads_left;
128 if ((num_threads % 2) == 1)
129 num_threads_left = num_threads / 2 + 1;
131 num_threads_left = num_threads / 2;
133 pivot_rank = n * num_threads_left / num_threads;
135 difference_type split =
136 parallel_sort_qs_divide(begin, end, comp, pivot_rank,
137 _Settings::get().sort_qs_num_samples_preset,
140 #pragma omp parallel sections num_threads(2)
143 parallel_sort_qs_conquer(begin, begin + split,
144 comp, num_threads_left);
146 parallel_sort_qs_conquer(begin + split, end,
147 comp, num_threads - num_threads_left);
153 /** @brief Unbalanced quicksort main call.
154 * @param begin Begin iterator of input sequence.
155 * @param end End iterator input sequence, ignored.
156 * @param comp Comparator.
157 * @param n Length of input sequence.
158 * @param num_threads Number of threads that are allowed to work on
161 template<typename RandomAccessIterator, typename Comparator>
163 parallel_sort_qs(RandomAccessIterator begin,
164 RandomAccessIterator end,
165 Comparator comp, typename std::iterator_traits
166 <RandomAccessIterator>::difference_type n,
171 typedef std::iterator_traits<RandomAccessIterator> traits_type;
172 typedef typename traits_type::value_type value_type;
173 typedef typename traits_type::difference_type difference_type;
178 // At least one element per processor.
180 num_threads = static_cast<thread_index_t>(n);
182 parallel_sort_qs_conquer(begin, begin + n, comp, num_threads);
185 } //namespace __gnu_parallel