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Diffstat (limited to 'libstdc++-v3/include/parallel/quicksort.h')
| -rw-r--r-- | libstdc++-v3/include/parallel/quicksort.h | 190 |
1 files changed, 190 insertions, 0 deletions
diff --git a/libstdc++-v3/include/parallel/quicksort.h b/libstdc++-v3/include/parallel/quicksort.h new file mode 100644 index 00000000000..de95549772a --- /dev/null +++ b/libstdc++-v3/include/parallel/quicksort.h @@ -0,0 +1,190 @@ +// -*- C++ -*- + +// Copyright (C) 2007, 2008 Free Software Foundation, Inc. +// +// This file is part of the GNU ISO C++ Library. This library is free +// software; you can redistribute it and/or modify it under the terms +// of the GNU General Public License as published by the Free Software +// Foundation; either version 2, or (at your option) any later +// version. + +// This library is distributed in the hope that it will be useful, but +// WITHOUT ANY WARRANTY; without even the implied warranty of +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +// General Public License for more details. + +// You should have received a copy of the GNU General Public License +// along with this library; see the file COPYING. If not, write to +// the Free Software Foundation, 59 Temple Place - Suite 330, Boston, +// MA 02111-1307, USA. + +// As a special exception, you may use this file as part of a free +// software library without restriction. Specifically, if other files +// instantiate templates or use macros or inline functions from this +// file, or you compile this file and link it with other files to +// produce an executable, this file does not by itself cause the +// resulting executable to be covered by the GNU General Public +// License. This exception does not however invalidate any other +// reasons why the executable file might be covered by the GNU General +// Public License. + +/** @file parallel/quicksort.h + * @brief Implementation of a unbalanced parallel quicksort (in-place). + * This file is a GNU parallel extension to the Standard C++ Library. + */ + +// Written by Johannes Singler. + +#ifndef _GLIBCXX_PARALLEL_QUICKSORT_H +#define _GLIBCXX_PARALLEL_QUICKSORT_H 1 + +#include <parallel/parallel.h> +#include <parallel/partition.h> + +namespace __gnu_parallel +{ + /** @brief Unbalanced quicksort divide step. + * @param begin Begin iterator of subsequence. + * @param end End iterator of subsequence. + * @param comp Comparator. + * @param pivot_rank Desired rank of the pivot. + * @param num_samples Choose pivot from that many samples. + * @param num_threads Number of threads that are allowed to work on + * this part. + */ + template<typename RandomAccessIterator, typename Comparator> + typename std::iterator_traits<RandomAccessIterator>::difference_type + parallel_sort_qs_divide(RandomAccessIterator begin, + RandomAccessIterator end, + Comparator comp, typename std::iterator_traits + <RandomAccessIterator>::difference_type pivot_rank, + typename std::iterator_traits + <RandomAccessIterator>::difference_type + num_samples, thread_index_t num_threads) + { + typedef std::iterator_traits<RandomAccessIterator> traits_type; + typedef typename traits_type::value_type value_type; + typedef typename traits_type::difference_type difference_type; + + difference_type n = end - begin; + num_samples = std::min(num_samples, n); + + // Allocate uninitialized, to avoid default constructor. + value_type* samples = + static_cast<value_type*>(::operator new(num_samples + * sizeof(value_type))); + + for (difference_type s = 0; s < num_samples; ++s) + { + const unsigned long long index = static_cast<unsigned long long>(s) + * n / num_samples; + ::new(&(samples[s])) value_type(begin[index]); + } + + __gnu_sequential::sort(samples, samples + num_samples, comp); + + value_type& pivot = samples[pivot_rank * num_samples / n]; + + __gnu_parallel::binder2nd<Comparator, value_type, value_type, bool> + pred(comp, pivot); + difference_type split = parallel_partition(begin, end, pred, num_threads); + + ::operator delete(samples); + + return split; + } + + /** @brief Unbalanced quicksort conquer step. + * @param begin Begin iterator of subsequence. + * @param end End iterator of subsequence. + * @param comp Comparator. + * @param num_threads Number of threads that are allowed to work on + * this part. + */ + template<typename RandomAccessIterator, typename Comparator> + void + parallel_sort_qs_conquer(RandomAccessIterator begin, + RandomAccessIterator end, + Comparator comp, + thread_index_t num_threads) + { + typedef std::iterator_traits<RandomAccessIterator> traits_type; + typedef typename traits_type::value_type value_type; + typedef typename traits_type::difference_type difference_type; + + if (num_threads <= 1) + { + __gnu_sequential::sort(begin, end, comp); + return; + } + + difference_type n = end - begin, pivot_rank; + + if (n <= 1) + return; + + thread_index_t num_threads_left; + + if ((num_threads % 2) == 1) + num_threads_left = num_threads / 2 + 1; + else + num_threads_left = num_threads / 2; + + pivot_rank = n * num_threads_left / num_threads; + + difference_type split = + parallel_sort_qs_divide(begin, end, comp, pivot_rank, + _Settings::get().sort_qs_num_samples_preset, + num_threads); + +#pragma omp parallel sections + { +#pragma omp section + parallel_sort_qs_conquer(begin, begin + split, + comp, num_threads_left); +#pragma omp section + parallel_sort_qs_conquer(begin + split, end, + comp, num_threads - num_threads_left); + } + } + + + + /** @brief Unbalanced quicksort main call. + * @param begin Begin iterator of input sequence. + * @param end End iterator input sequence, ignored. + * @param comp Comparator. + * @param n Length of input sequence. + * @param num_threads Number of threads that are allowed to work on + * this part. + */ + template<typename RandomAccessIterator, typename Comparator> + void + parallel_sort_qs(RandomAccessIterator begin, + RandomAccessIterator end, + Comparator comp, typename std::iterator_traits + <RandomAccessIterator>::difference_type n, + int num_threads) + { + _GLIBCXX_CALL(n) + + typedef std::iterator_traits<RandomAccessIterator> traits_type; + typedef typename traits_type::value_type value_type; + typedef typename traits_type::difference_type difference_type; + + if (n == 0) + return; + + // At least one element per processor. + if (num_threads > n) + num_threads = static_cast<thread_index_t>(n); + + // Hard to avoid. + omp_set_num_threads(num_threads); + + parallel_sort_qs_conquer(begin, begin + n, comp, num_threads); + } + +} //namespace __gnu_parallel + +#endif |