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// -*- C++ -*-
// Copyright (C) 2007, 2009 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
// Foundation; either version 3, or (at your option) any later
// version.
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file parallel/equally_split.h
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Johannes Singler.
#ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H
#define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1
namespace __gnu_parallel
{
/** @brief Function to split a sequence into parts of almost equal size.
*
* The resulting sequence s of length num_threads+1 contains the splitting
* positions when splitting the range [0,n) into parts of almost
* equal size (plus minus 1). The first entry is 0, the last one
* n. There may result empty parts.
* @param n Number of elements
* @param num_threads Number of parts
* @param s Splitters
* @returns End of splitter sequence, i. e. @c s+num_threads+1 */
template<typename difference_type, typename OutputIterator>
OutputIterator
equally_split(difference_type n, thread_index_t num_threads, OutputIterator s)
{
difference_type chunk_length = n / num_threads;
difference_type num_longer_chunks = n % num_threads;
difference_type pos = 0;
for (thread_index_t i = 0; i < num_threads; ++i)
{
*s++ = pos;
pos += (i < num_longer_chunks) ? (chunk_length + 1) : chunk_length;
}
*s++ = n;
return s;
}
/** @brief Function to split a sequence into parts of almost equal size.
*
* Returns the position of the splitting point between
* thread number thread_no (included) and
* thread number thread_no+1 (excluded).
* @param n Number of elements
* @param num_threads Number of parts
* @returns _SplittingAlgorithm point */
template<typename difference_type>
difference_type
equally_split_point(difference_type n,
thread_index_t num_threads,
thread_index_t thread_no)
{
difference_type chunk_length = n / num_threads;
difference_type num_longer_chunks = n % num_threads;
if (thread_no < num_longer_chunks)
return thread_no * (chunk_length + 1);
else
return num_longer_chunks * (chunk_length + 1)
+ (thread_no - num_longer_chunks) * chunk_length;
}
}
#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */
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