90 lines
3.3 KiB
C++
90 lines
3.3 KiB
C++
// -*- C++ -*-
|
|
|
|
// Copyright (C) 2007-2015 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 _DifferenceType, typename _OutputIterator>
|
|
_OutputIterator
|
|
__equally_split(_DifferenceType __n, _ThreadIndex __num_threads,
|
|
_OutputIterator __s)
|
|
{
|
|
_DifferenceType __chunk_length = __n / __num_threads;
|
|
_DifferenceType __num_longer_chunks = __n % __num_threads;
|
|
_DifferenceType __pos = 0;
|
|
for (_ThreadIndex __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
|
|
* @param __thread_no Number of threads
|
|
* @returns splitting point */
|
|
template<typename _DifferenceType>
|
|
_DifferenceType
|
|
__equally_split_point(_DifferenceType __n,
|
|
_ThreadIndex __num_threads,
|
|
_ThreadIndex __thread_no)
|
|
{
|
|
_DifferenceType __chunk_length = __n / __num_threads;
|
|
_DifferenceType __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 */
|