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Diffstat (limited to 'libstdc++-v3/include/parallel/equally_split.h')
| -rw-r--r-- | libstdc++-v3/include/parallel/equally_split.h | 88 |
1 files changed, 88 insertions, 0 deletions
diff --git a/libstdc++-v3/include/parallel/equally_split.h b/libstdc++-v3/include/parallel/equally_split.h new file mode 100644 index 000000000..481c98868 --- /dev/null +++ b/libstdc++-v3/include/parallel/equally_split.h @@ -0,0 +1,88 @@ +// -*- C++ -*- + +// Copyright (C) 2007, 2008, 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 _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 + * @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 */ |