88 lines
3.1 KiB
C++
88 lines
3.1 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007, 2009 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/equally_split.h
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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_EQUALLY_SPLIT_H
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#define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1
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namespace __gnu_parallel
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{
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/** @brief Function to split a sequence into parts of almost equal size.
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*
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* The resulting sequence s of length num_threads+1 contains the splitting
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* positions when splitting the range [0,n) into parts of almost
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* equal size (plus minus 1). The first entry is 0, the last one
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* n. There may result empty parts.
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* @param n Number of elements
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* @param num_threads Number of parts
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* @param s Splitters
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* @returns End of splitter sequence, i. e. @c s+num_threads+1 */
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template<typename difference_type, typename OutputIterator>
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OutputIterator
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equally_split(difference_type n, thread_index_t num_threads, OutputIterator s)
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{
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difference_type chunk_length = n / num_threads;
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difference_type num_longer_chunks = n % num_threads;
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difference_type pos = 0;
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for (thread_index_t i = 0; i < num_threads; ++i)
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{
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*s++ = pos;
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pos += (i < num_longer_chunks) ? (chunk_length + 1) : chunk_length;
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}
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*s++ = n;
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return s;
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}
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/** @brief Function to split a sequence into parts of almost equal size.
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*
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* Returns the position of the splitting point between
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* thread number thread_no (included) and
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* thread number thread_no+1 (excluded).
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* @param n Number of elements
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* @param num_threads Number of parts
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* @returns _SplittingAlgorithm point */
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template<typename difference_type>
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difference_type
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equally_split_point(difference_type n,
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thread_index_t num_threads,
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thread_index_t thread_no)
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{
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difference_type chunk_length = n / num_threads;
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difference_type num_longer_chunks = n % num_threads;
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if (thread_no < num_longer_chunks)
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return thread_no * (chunk_length + 1);
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else
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return num_longer_chunks * (chunk_length + 1)
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+ (thread_no - num_longer_chunks) * chunk_length;
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}
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}
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#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */
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