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496 lines
16 KiB
C++
496 lines
16 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2016 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/balanced_quicksort.h
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* @brief Implementation of a dynamically load-balanced parallel quicksort.
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*
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* It works in-place and needs only logarithmic extra memory.
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* The algorithm is similar to the one proposed in
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*
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* P. Tsigas and Y. Zhang.
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* A simple, fast parallel implementation of quicksort and
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* its performance evaluation on SUN enterprise 10000.
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* In 11th Euromicro Conference on Parallel, Distributed and
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* Network-Based Processing, page 372, 2003.
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*
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* This file is a GNU parallel extension to the Standard C++ Library.
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*/
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// Written by Johannes Singler.
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#ifndef _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H
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#define _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H 1
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#include <parallel/basic_iterator.h>
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#include <bits/stl_algo.h>
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#include <bits/stl_function.h>
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#include <parallel/settings.h>
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#include <parallel/partition.h>
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#include <parallel/random_number.h>
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#include <parallel/queue.h>
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#if _GLIBCXX_ASSERTIONS
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#include <parallel/checkers.h>
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#ifdef _GLIBCXX_HAVE_UNISTD_H
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#include <unistd.h>
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#endif
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#endif
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namespace __gnu_parallel
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{
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/** @brief Information local to one thread in the parallel quicksort run. */
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template<typename _RAIter>
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struct _QSBThreadLocal
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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/** @brief Continuous part of the sequence, described by an
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iterator pair. */
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typedef std::pair<_RAIter, _RAIter> _Piece;
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/** @brief Initial piece to work on. */
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_Piece _M_initial;
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/** @brief Work-stealing queue. */
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_RestrictedBoundedConcurrentQueue<_Piece> _M_leftover_parts;
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/** @brief Number of threads involved in this algorithm. */
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_ThreadIndex _M_num_threads;
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/** @brief Pointer to a counter of elements left over to sort. */
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volatile _DifferenceType* _M_elements_leftover;
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/** @brief The complete sequence to sort. */
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_Piece _M_global;
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/** @brief Constructor.
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* @param __queue_size size of the work-stealing queue. */
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_QSBThreadLocal(int __queue_size) : _M_leftover_parts(__queue_size) { }
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};
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/** @brief Balanced quicksort divide step.
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* @param __begin Begin iterator of subsequence.
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* @param __end End iterator of subsequence.
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* @param __comp Comparator.
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* @param __num_threads Number of threads that are allowed to work on
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* this part.
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* @pre @c (__end-__begin)>=1 */
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template<typename _RAIter, typename _Compare>
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typename std::iterator_traits<_RAIter>::difference_type
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__qsb_divide(_RAIter __begin, _RAIter __end,
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_Compare __comp, _ThreadIndex __num_threads)
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{
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_GLIBCXX_PARALLEL_ASSERT(__num_threads > 0);
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_RAIter __pivot_pos =
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__median_of_three_iterators(__begin, __begin + (__end - __begin) / 2,
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__end - 1, __comp);
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#if defined(_GLIBCXX_ASSERTIONS)
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// Must be in between somewhere.
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_DifferenceType __n = __end - __begin;
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_GLIBCXX_PARALLEL_ASSERT((!__comp(*__pivot_pos, *__begin)
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&& !__comp(*(__begin + __n / 2),
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*__pivot_pos))
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|| (!__comp(*__pivot_pos, *__begin)
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&& !__comp(*(__end - 1), *__pivot_pos))
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|| (!__comp(*__pivot_pos, *(__begin + __n / 2))
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&& !__comp(*__begin, *__pivot_pos))
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|| (!__comp(*__pivot_pos, *(__begin + __n / 2))
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&& !__comp(*(__end - 1), *__pivot_pos))
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|| (!__comp(*__pivot_pos, *(__end - 1))
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&& !__comp(*__begin, *__pivot_pos))
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|| (!__comp(*__pivot_pos, *(__end - 1))
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&& !__comp(*(__begin + __n / 2),
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*__pivot_pos)));
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#endif
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// Swap pivot value to end.
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if (__pivot_pos != (__end - 1))
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std::iter_swap(__pivot_pos, __end - 1);
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__pivot_pos = __end - 1;
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__gnu_parallel::__binder2nd<_Compare, _ValueType, _ValueType, bool>
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__pred(__comp, *__pivot_pos);
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// Divide, returning __end - __begin - 1 in the worst case.
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_DifferenceType __split_pos = __parallel_partition(__begin, __end - 1,
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__pred,
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__num_threads);
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// Swap back pivot to middle.
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std::iter_swap(__begin + __split_pos, __pivot_pos);
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__pivot_pos = __begin + __split_pos;
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#if _GLIBCXX_ASSERTIONS
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_RAIter __r;
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for (__r = __begin; __r != __pivot_pos; ++__r)
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_GLIBCXX_PARALLEL_ASSERT(__comp(*__r, *__pivot_pos));
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for (; __r != __end; ++__r)
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_GLIBCXX_PARALLEL_ASSERT(!__comp(*__r, *__pivot_pos));
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#endif
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return __split_pos;
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}
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/** @brief Quicksort conquer step.
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* @param __tls Array of thread-local storages.
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* @param __begin Begin iterator of subsequence.
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* @param __end End iterator of subsequence.
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* @param __comp Comparator.
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* @param __iam Number of the thread processing this function.
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* @param __num_threads
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* Number of threads that are allowed to work on this part. */
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template<typename _RAIter, typename _Compare>
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void
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__qsb_conquer(_QSBThreadLocal<_RAIter>** __tls,
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_RAIter __begin, _RAIter __end,
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_Compare __comp,
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_ThreadIndex __iam, _ThreadIndex __num_threads,
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bool __parent_wait)
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_DifferenceType __n = __end - __begin;
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if (__num_threads <= 1 || __n <= 1)
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{
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__tls[__iam]->_M_initial.first = __begin;
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__tls[__iam]->_M_initial.second = __end;
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__qsb_local_sort_with_helping(__tls, __comp, __iam, __parent_wait);
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return;
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}
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// Divide step.
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_DifferenceType __split_pos =
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__qsb_divide(__begin, __end, __comp, __num_threads);
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(0 <= __split_pos &&
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__split_pos < (__end - __begin));
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#endif
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_ThreadIndex
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__num_threads_leftside = std::max<_ThreadIndex>
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(1, std::min<_ThreadIndex>(__num_threads - 1, __split_pos
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* __num_threads / __n));
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# pragma omp atomic
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*__tls[__iam]->_M_elements_leftover -= (_DifferenceType)1;
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// Conquer step.
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# pragma omp parallel num_threads(2)
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{
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bool __wait;
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if(omp_get_num_threads() < 2)
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__wait = false;
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else
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__wait = __parent_wait;
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# pragma omp sections
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{
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# pragma omp section
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{
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__qsb_conquer(__tls, __begin, __begin + __split_pos, __comp,
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__iam, __num_threads_leftside, __wait);
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__wait = __parent_wait;
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}
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// The pivot_pos is left in place, to ensure termination.
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# pragma omp section
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{
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__qsb_conquer(__tls, __begin + __split_pos + 1, __end, __comp,
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__iam + __num_threads_leftside,
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__num_threads - __num_threads_leftside, __wait);
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__wait = __parent_wait;
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}
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}
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}
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}
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/**
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* @brief Quicksort step doing load-balanced local sort.
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* @param __tls Array of thread-local storages.
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* @param __comp Comparator.
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* @param __iam Number of the thread processing this function.
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*/
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template<typename _RAIter, typename _Compare>
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void
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__qsb_local_sort_with_helping(_QSBThreadLocal<_RAIter>** __tls,
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_Compare& __comp, _ThreadIndex __iam,
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bool __wait)
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{
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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typedef std::pair<_RAIter, _RAIter> _Piece;
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_QSBThreadLocal<_RAIter>& __tl = *__tls[__iam];
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_DifferenceType
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__base_case_n = _Settings::get().sort_qsb_base_case_maximal_n;
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if (__base_case_n < 2)
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__base_case_n = 2;
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_ThreadIndex __num_threads = __tl._M_num_threads;
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// Every thread has its own random number generator.
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_RandomNumber __rng(__iam + 1);
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_Piece __current = __tl._M_initial;
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_DifferenceType __elements_done = 0;
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#if _GLIBCXX_ASSERTIONS
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_DifferenceType __total_elements_done = 0;
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#endif
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for (;;)
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{
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// Invariant: __current must be a valid (maybe empty) range.
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_RAIter __begin = __current.first, __end = __current.second;
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_DifferenceType __n = __end - __begin;
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if (__n > __base_case_n)
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{
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// Divide.
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_RAIter __pivot_pos = __begin + __rng(__n);
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// Swap __pivot_pos value to end.
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if (__pivot_pos != (__end - 1))
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std::iter_swap(__pivot_pos, __end - 1);
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__pivot_pos = __end - 1;
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__gnu_parallel::__binder2nd
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<_Compare, _ValueType, _ValueType, bool>
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__pred(__comp, *__pivot_pos);
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// Divide, leave pivot unchanged in last place.
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_RAIter __split_pos1, __split_pos2;
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__split_pos1 = __gnu_sequential::partition(__begin, __end - 1,
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__pred);
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// Left side: < __pivot_pos; __right side: >= __pivot_pos.
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(__begin <= __split_pos1
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&& __split_pos1 < __end);
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#endif
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// Swap pivot back to middle.
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if (__split_pos1 != __pivot_pos)
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std::iter_swap(__split_pos1, __pivot_pos);
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__pivot_pos = __split_pos1;
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// In case all elements are equal, __split_pos1 == 0.
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if ((__split_pos1 + 1 - __begin) < (__n >> 7)
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|| (__end - __split_pos1) < (__n >> 7))
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{
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// Very unequal split, one part smaller than one 128th
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// elements not strictly larger than the pivot.
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__gnu_parallel::__unary_negate<__gnu_parallel::__binder1st
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<_Compare, _ValueType, _ValueType, bool>, _ValueType>
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__pred(__gnu_parallel::__binder1st
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<_Compare, _ValueType, _ValueType, bool>
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(__comp, *__pivot_pos));
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// Find other end of pivot-equal range.
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__split_pos2 = __gnu_sequential::partition(__split_pos1 + 1,
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__end, __pred);
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}
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else
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// Only skip the pivot.
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__split_pos2 = __split_pos1 + 1;
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// Elements equal to pivot are done.
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__elements_done += (__split_pos2 - __split_pos1);
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#if _GLIBCXX_ASSERTIONS
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__total_elements_done += (__split_pos2 - __split_pos1);
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#endif
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// Always push larger part onto stack.
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if (((__split_pos1 + 1) - __begin) < (__end - (__split_pos2)))
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{
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// Right side larger.
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if ((__split_pos2) != __end)
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__tl._M_leftover_parts.push_front
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(std::make_pair(__split_pos2, __end));
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//__current.first = __begin; //already set anyway
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__current.second = __split_pos1;
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continue;
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}
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else
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{
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// Left side larger.
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if (__begin != __split_pos1)
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__tl._M_leftover_parts.push_front(std::make_pair
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(__begin, __split_pos1));
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__current.first = __split_pos2;
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//__current.second = __end; //already set anyway
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continue;
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}
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}
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else
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{
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__gnu_sequential::sort(__begin, __end, __comp);
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__elements_done += __n;
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#if _GLIBCXX_ASSERTIONS
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__total_elements_done += __n;
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#endif
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// Prefer own stack, small pieces.
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if (__tl._M_leftover_parts.pop_front(__current))
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continue;
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# pragma omp atomic
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*__tl._M_elements_leftover -= __elements_done;
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__elements_done = 0;
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#if _GLIBCXX_ASSERTIONS
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double __search_start = omp_get_wtime();
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#endif
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// Look for new work.
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bool __successfully_stolen = false;
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while (__wait && *__tl._M_elements_leftover > 0
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&& !__successfully_stolen
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#if _GLIBCXX_ASSERTIONS
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// Possible dead-lock.
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&& (omp_get_wtime() < (__search_start + 1.0))
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#endif
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)
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{
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_ThreadIndex __victim;
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__victim = __rng(__num_threads);
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// Large pieces.
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__successfully_stolen = (__victim != __iam)
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&& __tls[__victim]->_M_leftover_parts.pop_back(__current);
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if (!__successfully_stolen)
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__yield();
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#if !defined(__ICC) && !defined(__ECC)
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# pragma omp flush
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#endif
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}
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#if _GLIBCXX_ASSERTIONS
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if (omp_get_wtime() >= (__search_start + 1.0))
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{
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sleep(1);
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_GLIBCXX_PARALLEL_ASSERT(omp_get_wtime()
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< (__search_start + 1.0));
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}
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#endif
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if (!__successfully_stolen)
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{
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(*__tl._M_elements_leftover == 0);
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#endif
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return;
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}
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}
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}
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}
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/** @brief Top-level quicksort routine.
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* @param __begin Begin iterator of sequence.
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* @param __end End iterator of sequence.
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* @param __comp Comparator.
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* @param __num_threads Number of threads that are allowed to work on
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* this part.
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*/
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template<typename _RAIter, typename _Compare>
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void
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__parallel_sort_qsb(_RAIter __begin, _RAIter __end,
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_Compare __comp, _ThreadIndex __num_threads)
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{
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_GLIBCXX_CALL(__end - __begin)
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typedef std::iterator_traits<_RAIter> _TraitsType;
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typedef typename _TraitsType::value_type _ValueType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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typedef std::pair<_RAIter, _RAIter> _Piece;
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typedef _QSBThreadLocal<_RAIter> _TLSType;
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_DifferenceType __n = __end - __begin;
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if (__n <= 1)
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return;
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// At least one element per processor.
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if (__num_threads > __n)
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__num_threads = static_cast<_ThreadIndex>(__n);
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// Initialize thread local storage
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_TLSType** __tls = new _TLSType*[__num_threads];
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_DifferenceType __queue_size = (__num_threads
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* (_ThreadIndex)(__rd_log2(__n) + 1));
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for (_ThreadIndex __t = 0; __t < __num_threads; ++__t)
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__tls[__t] = new _QSBThreadLocal<_RAIter>(__queue_size);
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// There can never be more than ceil(__rd_log2(__n)) ranges on the
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// stack, because
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// 1. Only one processor pushes onto the stack
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// 2. The largest range has at most length __n
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// 3. Each range is larger than half of the range remaining
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volatile _DifferenceType __elements_leftover = __n;
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for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
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{
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__tls[__i]->_M_elements_leftover = &__elements_leftover;
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__tls[__i]->_M_num_threads = __num_threads;
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__tls[__i]->_M_global = std::make_pair(__begin, __end);
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// Just in case nothing is left to assign.
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__tls[__i]->_M_initial = std::make_pair(__end, __end);
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}
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// Main recursion call.
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__qsb_conquer(__tls, __begin, __begin + __n, __comp, 0,
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__num_threads, true);
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#if _GLIBCXX_ASSERTIONS
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// All stack must be empty.
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_Piece __dummy;
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for (_ThreadIndex __i = 1; __i < __num_threads; ++__i)
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_GLIBCXX_PARALLEL_ASSERT(
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!__tls[__i]->_M_leftover_parts.pop_back(__dummy));
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#endif
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for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
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delete __tls[__i];
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delete[] __tls;
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}
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} // namespace __gnu_parallel
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#endif /* _GLIBCXX_PARALLEL_BALANCED_QUICKSORT_H */
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