1 // -*- C++ -*- 2 3 // Copyright (C) 2007-2013 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the terms 7 // of the GNU General Public License as published by the Free Software 8 // Foundation; either version 3, or (at your option) any later 9 // version. 10 11 // This library is distributed in the hope that it will be useful, but 12 // WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14 // General Public License for more details. 15 16 // Under Section 7 of GPL version 3, you are granted additional 17 // permissions described in the GCC Runtime Library Exception, version 18 // 3.1, as published by the Free Software Foundation. 19 20 // You should have received a copy of the GNU General Public License and 21 // a copy of the GCC Runtime Library Exception along with this program; 22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see 23 // <http://www.gnu.org/licenses/>. 24 25 /** @file parallel/equally_split.h 26 * This file is a GNU parallel extension to the Standard C++ Library. 27 */ 28 29 // Written by Johannes Singler. 30 31 #ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 32 #define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1 33 34 namespace __gnu_parallel 35 { 36 /** @brief function to split a sequence into parts of almost equal size. 37 * 38 * The resulting sequence __s of length __num_threads+1 contains the 39 * splitting positions when splitting the range [0,__n) into parts of 40 * almost equal size (plus minus 1). The first entry is 0, the last 41 * one n. There may result empty parts. 42 * @param __n Number of elements 43 * @param __num_threads Number of parts 44 * @param __s Splitters 45 * @returns End of __splitter sequence, i.e. @c __s+__num_threads+1 */ 46 template<typename _DifferenceType, typename _OutputIterator> 47 _OutputIterator 48 __equally_split(_DifferenceType __n, _ThreadIndex __num_threads, 49 _OutputIterator __s) 50 { 51 _DifferenceType __chunk_length = __n / __num_threads; 52 _DifferenceType __num_longer_chunks = __n % __num_threads; 53 _DifferenceType __pos = 0; 54 for (_ThreadIndex __i = 0; __i < __num_threads; ++__i) 55 { 56 *__s++ = __pos; 57 __pos += ((__i < __num_longer_chunks) 58 ? (__chunk_length + 1) : __chunk_length); 59 } 60 *__s++ = __n; 61 return __s; 62 } 63 64 /** @brief function to split a sequence into parts of almost equal size. 65 * 66 * Returns the position of the splitting point between 67 * thread number __thread_no (included) and 68 * thread number __thread_no+1 (excluded). 69 * @param __n Number of elements 70 * @param __num_threads Number of parts 71 * @param __thread_no Number of threads 72 * @returns splitting point */ 73 template<typename _DifferenceType> 74 _DifferenceType 75 __equally_split_point(_DifferenceType __n, 76 _ThreadIndex __num_threads, 77 _ThreadIndex __thread_no) 78 { 79 _DifferenceType __chunk_length = __n / __num_threads; 80 _DifferenceType __num_longer_chunks = __n % __num_threads; 81 if (__thread_no < __num_longer_chunks) 82 return __thread_no * (__chunk_length + 1); 83 else 84 return __num_longer_chunks * (__chunk_length + 1) 85 + (__thread_no - __num_longer_chunks) * __chunk_length; 86 } 87 } 88 89 #endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */ 90
