90 lines
3.3 KiB
C++
90 lines
3.3 KiB
C++
// -*- 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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// 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
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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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/** @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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#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */
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