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- // -*- C++ -*-
- // Copyright (C) 2007-2022 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 _RAIter, typename _Compare>
- typename 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)
- {
- typedef std::iterator_traits<_RAIter> _TraitsType;
- typedef typename _TraitsType::value_type _ValueType;
- typedef typename _TraitsType::difference_type _DifferenceType;
- _DifferenceType __n = __end - __begin;
- __num_samples = std::min(__num_samples, __n);
- // Allocate uninitialized, to avoid default constructor.
- _ValueType* __samples = static_cast<_ValueType*>
- (::operator new(__num_samples * sizeof(_ValueType)));
- for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
- {
- const unsigned long long __index = static_cast<unsigned long long>
- (__s) * __n / __num_samples;
- ::new(&(__samples[__s])) _ValueType(__begin[__index]);
- }
- __gnu_sequential::sort(__samples, __samples + __num_samples, __comp);
- _ValueType& __pivot = __samples[__pivot_rank * __num_samples / __n];
- __gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool>
- __pred(__comp, __pivot);
- _DifferenceType __split = __parallel_partition(__begin, __end,
- __pred, __num_threads);
- for (_DifferenceType __s = 0; __s < __num_samples; ++__s)
- __samples[__s].~_ValueType();
- ::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 _RAIter, typename _Compare>
- void
- __parallel_sort_qs_conquer(_RAIter __begin, _RAIter __end,
- _Compare __comp,
- _ThreadIndex __num_threads)
- {
- typedef std::iterator_traits<_RAIter> _TraitsType;
- typedef typename _TraitsType::value_type _ValueType;
- typedef typename _TraitsType::difference_type _DifferenceType;
- if (__num_threads <= 1)
- {
- __gnu_sequential::sort(__begin, __end, __comp);
- return;
- }
- _DifferenceType __n = __end - __begin, __pivot_rank;
- if (__n <= 1)
- return;
- _ThreadIndex __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;
- _DifferenceType __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 _RAIter, typename _Compare>
- void
- __parallel_sort_qs(_RAIter __begin, _RAIter __end,
- _Compare __comp,
- _ThreadIndex __num_threads)
- {
- _GLIBCXX_CALL(__n)
- typedef std::iterator_traits<_RAIter> _TraitsType;
- typedef typename _TraitsType::value_type _ValueType;
- typedef typename _TraitsType::difference_type _DifferenceType;
- _DifferenceType __n = __end - __begin;
- // At least one element per processor.
- if (__num_threads > __n)
- __num_threads = static_cast<_ThreadIndex>(__n);
- __parallel_sort_qs_conquer(
- __begin, __begin + __n, __comp, __num_threads);
- }
- } //namespace __gnu_parallel
- #endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */
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