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// -*- C++ -*- |
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// Copyright (C) 2007-2021 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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|
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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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|
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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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|
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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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|
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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 |
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* splitting positions when splitting the range [0,__n) into parts of |
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* almost equal size (plus minus 1). The first entry is 0, the last |
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* one 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 _DifferenceType, typename _OutputIterator> |
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_OutputIterator |
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__equally_split(_DifferenceType __n, _ThreadIndex __num_threads, |
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_OutputIterator __s) |
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{ |
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_DifferenceType __chunk_length = __n / __num_threads; |
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_DifferenceType __num_longer_chunks = __n % __num_threads; |
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_DifferenceType __pos = 0; |
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for (_ThreadIndex __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) |
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? (__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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|
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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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* @param __thread_no Number of threads |
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* @returns splitting point */ |
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template<typename _DifferenceType> |
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_DifferenceType |
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__equally_split_point(_DifferenceType __n, |
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_ThreadIndex __num_threads, |
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_ThreadIndex __thread_no) |
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{ |
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_DifferenceType __chunk_length = __n / __num_threads; |
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_DifferenceType __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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|
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#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */ |
