| // -*- C++ -*- |
| |
| // Copyright (C) 2007, 2008, 2009 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 3, 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. |
| |
| // Under Section 7 of GPL version 3, you are granted additional |
| // permissions described in the GCC Runtime Library Exception, version |
| // 3.1, as published by the Free Software Foundation. |
| |
| // You should have received a copy of the GNU General Public License and |
| // a copy of the GCC Runtime Library Exception along with this program; |
| // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see |
| // <http://www.gnu.org/licenses/>. |
| |
| /** @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 num_threads(2) |
| { |
| #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 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, |
| thread_index_t 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; |
| |
| difference_type n = end - begin; |
| |
| // At least one element per processor. |
| if (num_threads > n) |
| num_threads = static_cast<thread_index_t>(n); |
| |
| parallel_sort_qs_conquer(begin, begin + n, comp, num_threads); |
| } |
| |
| } //namespace __gnu_parallel |
| |
| #endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */ |