| // -*- 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 */ |