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435 lines
15 KiB
C++
435 lines
15 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2014 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/partition.h
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* @brief Parallel implementation of std::partition(),
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* std::nth_element(), and std::partial_sort().
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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 and Felix Putze.
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#ifndef _GLIBCXX_PARALLEL_PARTITION_H
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#define _GLIBCXX_PARALLEL_PARTITION_H 1
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#include <parallel/basic_iterator.h>
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#include <parallel/sort.h>
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#include <parallel/random_number.h>
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#include <bits/stl_algo.h>
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#include <parallel/parallel.h>
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/** @brief Decide whether to declare certain variables volatile. */
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#define _GLIBCXX_VOLATILE volatile
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namespace __gnu_parallel
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{
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/** @brief Parallel implementation of std::partition.
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* @param __begin Begin iterator of input sequence to split.
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* @param __end End iterator of input sequence to split.
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* @param __pred Partition predicate, possibly including some kind
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* of pivot.
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* @param __num_threads Maximum number of threads to use for this task.
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* @return Number of elements not fulfilling the predicate. */
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template<typename _RAIter, typename _Predicate>
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typename std::iterator_traits<_RAIter>::difference_type
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__parallel_partition(_RAIter __begin, _RAIter __end,
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_Predicate __pred, _ThreadIndex __num_threads)
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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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_GLIBCXX_CALL(__n)
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const _Settings& __s = _Settings::get();
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// shared
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_GLIBCXX_VOLATILE _DifferenceType __left = 0, __right = __n - 1,
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__dist = __n,
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__leftover_left, __leftover_right,
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__leftnew, __rightnew;
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// just 0 or 1, but int to allow atomic operations
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int* __reserved_left = 0, * __reserved_right = 0;
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_DifferenceType __chunk_size = __s.partition_chunk_size;
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//at least two chunks per thread
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if (__dist >= 2 * __num_threads * __chunk_size)
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# pragma omp parallel num_threads(__num_threads)
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{
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# pragma omp single
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{
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__num_threads = omp_get_num_threads();
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__reserved_left = new int[__num_threads];
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__reserved_right = new int[__num_threads];
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if (__s.partition_chunk_share > 0.0)
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__chunk_size = std::max<_DifferenceType>
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(__s.partition_chunk_size, (double)__n
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* __s.partition_chunk_share / (double)__num_threads);
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else
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__chunk_size = __s.partition_chunk_size;
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}
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while (__dist >= 2 * __num_threads * __chunk_size)
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{
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# pragma omp single
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{
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_DifferenceType __num_chunks = __dist / __chunk_size;
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for (_ThreadIndex __r = 0; __r < __num_threads; ++__r)
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{
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__reserved_left [__r] = 0; // false
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__reserved_right[__r] = 0; // false
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}
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__leftover_left = 0;
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__leftover_right = 0;
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} //implicit barrier
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// Private.
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_DifferenceType __thread_left, __thread_left_border,
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__thread_right, __thread_right_border;
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__thread_left = __left + 1;
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// Just to satisfy the condition below.
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__thread_left_border = __thread_left - 1;
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__thread_right = __n - 1;
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// Just to satisfy the condition below.
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__thread_right_border = __thread_right + 1;
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bool __iam_finished = false;
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while (!__iam_finished)
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{
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if (__thread_left > __thread_left_border)
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{
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_DifferenceType __former_dist =
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__fetch_and_add(&__dist, -__chunk_size);
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if (__former_dist < __chunk_size)
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{
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__fetch_and_add(&__dist, __chunk_size);
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__iam_finished = true;
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break;
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}
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else
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{
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__thread_left =
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__fetch_and_add(&__left, __chunk_size);
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__thread_left_border =
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__thread_left + (__chunk_size - 1);
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}
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}
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if (__thread_right < __thread_right_border)
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{
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_DifferenceType __former_dist =
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__fetch_and_add(&__dist, -__chunk_size);
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if (__former_dist < __chunk_size)
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{
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__fetch_and_add(&__dist, __chunk_size);
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__iam_finished = true;
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break;
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}
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else
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{
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__thread_right =
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__fetch_and_add(&__right, -__chunk_size);
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__thread_right_border =
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__thread_right - (__chunk_size - 1);
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}
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}
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// Swap as usual.
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while (__thread_left < __thread_right)
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{
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while (__pred(__begin[__thread_left])
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&& __thread_left <= __thread_left_border)
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++__thread_left;
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while (!__pred(__begin[__thread_right])
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&& __thread_right >= __thread_right_border)
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--__thread_right;
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if (__thread_left > __thread_left_border
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|| __thread_right < __thread_right_border)
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// Fetch new chunk(__s).
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break;
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std::iter_swap(__begin + __thread_left,
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__begin + __thread_right);
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++__thread_left;
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--__thread_right;
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}
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}
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// Now swap the leftover chunks to the right places.
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if (__thread_left <= __thread_left_border)
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# pragma omp atomic
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++__leftover_left;
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if (__thread_right >= __thread_right_border)
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# pragma omp atomic
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++__leftover_right;
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# pragma omp barrier
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_DifferenceType
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__leftold = __left,
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__leftnew = __left - __leftover_left * __chunk_size,
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__rightold = __right,
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__rightnew = __right + __leftover_right * __chunk_size;
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// <=> __thread_left_border + (__chunk_size - 1) >= __leftnew
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if (__thread_left <= __thread_left_border
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&& __thread_left_border >= __leftnew)
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{
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// Chunk already in place, reserve spot.
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__reserved_left[(__left - (__thread_left_border + 1))
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/ __chunk_size] = 1;
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}
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// <=> __thread_right_border - (__chunk_size - 1) <= __rightnew
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if (__thread_right >= __thread_right_border
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&& __thread_right_border <= __rightnew)
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{
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// Chunk already in place, reserve spot.
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__reserved_right[((__thread_right_border - 1) - __right)
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/ __chunk_size] = 1;
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}
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# pragma omp barrier
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if (__thread_left <= __thread_left_border
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&& __thread_left_border < __leftnew)
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{
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// Find spot and swap.
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_DifferenceType __swapstart = -1;
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for (int __r = 0; __r < __leftover_left; ++__r)
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if (__reserved_left[__r] == 0
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&& __compare_and_swap(&(__reserved_left[__r]), 0, 1))
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{
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__swapstart = __leftold - (__r + 1) * __chunk_size;
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break;
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}
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1);
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#endif
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std::swap_ranges(__begin + __thread_left_border
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- (__chunk_size - 1),
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__begin + __thread_left_border + 1,
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__begin + __swapstart);
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}
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if (__thread_right >= __thread_right_border
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&& __thread_right_border > __rightnew)
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{
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// Find spot and swap
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_DifferenceType __swapstart = -1;
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for (int __r = 0; __r < __leftover_right; ++__r)
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if (__reserved_right[__r] == 0
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&& __compare_and_swap(&(__reserved_right[__r]), 0, 1))
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{
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__swapstart = __rightold + __r * __chunk_size + 1;
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break;
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}
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(__swapstart != -1);
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#endif
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std::swap_ranges(__begin + __thread_right_border,
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__begin + __thread_right_border
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+ __chunk_size, __begin + __swapstart);
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}
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#if _GLIBCXX_ASSERTIONS
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# pragma omp barrier
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# pragma omp single
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{
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for (_DifferenceType __r = 0; __r < __leftover_left; ++__r)
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_GLIBCXX_PARALLEL_ASSERT(__reserved_left[__r] == 1);
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for (_DifferenceType __r = 0; __r < __leftover_right; ++__r)
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_GLIBCXX_PARALLEL_ASSERT(__reserved_right[__r] == 1);
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}
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#endif
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__left = __leftnew;
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__right = __rightnew;
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__dist = __right - __left + 1;
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}
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# pragma omp flush(__left, __right)
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} // end "recursion" //parallel
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_DifferenceType __final_left = __left, __final_right = __right;
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while (__final_left < __final_right)
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{
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// Go right until key is geq than pivot.
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while (__pred(__begin[__final_left])
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&& __final_left < __final_right)
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++__final_left;
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// Go left until key is less than pivot.
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while (!__pred(__begin[__final_right])
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&& __final_left < __final_right)
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--__final_right;
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if (__final_left == __final_right)
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break;
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std::iter_swap(__begin + __final_left, __begin + __final_right);
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++__final_left;
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--__final_right;
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}
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// All elements on the left side are < piv, all elements on the
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// right are >= piv
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delete[] __reserved_left;
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delete[] __reserved_right;
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// Element "between" __final_left and __final_right might not have
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// been regarded yet
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if (__final_left < __n && !__pred(__begin[__final_left]))
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// Really swapped.
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return __final_left;
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else
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return __final_left + 1;
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}
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/**
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* @brief Parallel implementation of std::nth_element().
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* @param __begin Begin iterator of input sequence.
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* @param __nth _Iterator of element that must be in position afterwards.
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* @param __end End iterator of input sequence.
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* @param __comp Comparator.
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*/
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template<typename _RAIter, typename _Compare>
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void
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__parallel_nth_element(_RAIter __begin, _RAIter __nth,
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_RAIter __end, _Compare __comp)
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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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_GLIBCXX_CALL(__end - __begin)
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_RAIter __split;
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_RandomNumber __rng;
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const _Settings& __s = _Settings::get();
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_DifferenceType __minimum_length = std::max<_DifferenceType>(2,
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std::max(__s.nth_element_minimal_n, __s.partition_minimal_n));
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// Break if input range to small.
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while (static_cast<_SequenceIndex>(__end - __begin) >= __minimum_length)
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{
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_DifferenceType __n = __end - __begin;
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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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// _Compare must have first_value_type, second_value_type,
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// result_type
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// _Compare ==
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// __gnu_parallel::_Lexicographic<S, int,
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// __gnu_parallel::_Less<S, S> >
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// __pivot_pos == std::pair<S, int>*
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__gnu_parallel::__binder2nd<_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 = __begin + __parallel_partition(__begin, __end - 1,
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__pred,
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__get_max_threads());
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// Left side: < __pivot_pos; __right side: >= __pivot_pos
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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::
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__binder1st<_Compare, _ValueType,
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_ValueType, bool>, _ValueType>
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__pred(__gnu_parallel::__binder1st<_Compare, _ValueType,
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_ValueType, bool>(__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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// Compare iterators.
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if (__split_pos2 <= __nth)
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__begin = __split_pos2;
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else if (__nth < __split_pos1)
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__end = __split_pos1;
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else
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break;
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}
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// Only at most _Settings::partition_minimal_n __elements __left.
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__gnu_sequential::nth_element(__begin, __nth, __end, __comp);
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}
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/** @brief Parallel implementation of std::partial_sort().
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* @param __begin Begin iterator of input sequence.
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* @param __middle Sort until this position.
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* @param __end End iterator of input sequence.
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* @param __comp Comparator. */
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template<typename _RAIter, typename _Compare>
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void
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__parallel_partial_sort(_RAIter __begin,
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_RAIter __middle,
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_RAIter __end, _Compare __comp)
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{
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__parallel_nth_element(__begin, __middle, __end, __comp);
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std::sort(__begin, __middle, __comp);
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}
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} //namespace __gnu_parallel
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#undef _GLIBCXX_VOLATILE
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#endif /* _GLIBCXX_PARALLEL_PARTITION_H */
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