// -*- C++ -*- // Copyright (C) 2007-2018 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 // . /** @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 _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 _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 */