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6482a45c | 1 | // -*- C++ -*- |
2 | ||
f1717362 | 3 | // Copyright (C) 2007-2016 Free Software Foundation, Inc. |
6482a45c | 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 | |
6bc9506f | 8 | // Foundation; either version 3, or (at your option) any later |
6482a45c | 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 | ||
6bc9506f | 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. | |
6482a45c | 19 | |
6bc9506f | 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/>. | |
6482a45c | 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 | { | |
757532bc | 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 | |
73337dee | 45 | * @returns End of __splitter sequence, i.e. @c __s+__num_threads+1 */ |
757532bc | 46 | template<typename _DifferenceType, typename _OutputIterator> |
47 | _OutputIterator | |
c62677d7 | 48 | __equally_split(_DifferenceType __n, _ThreadIndex __num_threads, |
49 | _OutputIterator __s) | |
757532bc | 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 | } | |
7956748e | 63 | |
757532bc | 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 | |
db3b35cb | 71 | * @param __thread_no Number of threads |
757532bc | 72 | * @returns splitting point */ |
73 | template<typename _DifferenceType> | |
74 | _DifferenceType | |
c62677d7 | 75 | __equally_split_point(_DifferenceType __n, |
76 | _ThreadIndex __num_threads, | |
77 | _ThreadIndex __thread_no) | |
757532bc | 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) | |
34475802 | 85 | + (__thread_no - __num_longer_chunks) * __chunk_length; |
757532bc | 86 | } |
6482a45c | 87 | } |
88 | ||
a8aa9db5 | 89 | #endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */ |