xref: /dflybsd-src/contrib/gcc-8.0/libstdc++-v3/include/parallel/equally_split.h (revision 38fd149817dfbff97799f62fcb70be98c4e32523)
1*38fd1498Szrj // -*- C++ -*-
2*38fd1498Szrj 
3*38fd1498Szrj // Copyright (C) 2007-2018 Free Software Foundation, Inc.
4*38fd1498Szrj //
5*38fd1498Szrj // This file is part of the GNU ISO C++ Library.  This library is free
6*38fd1498Szrj // software; you can redistribute it and/or modify it under the terms
7*38fd1498Szrj // of the GNU General Public License as published by the Free Software
8*38fd1498Szrj // Foundation; either version 3, or (at your option) any later
9*38fd1498Szrj // version.
10*38fd1498Szrj 
11*38fd1498Szrj // This library is distributed in the hope that it will be useful, but
12*38fd1498Szrj // WITHOUT ANY WARRANTY; without even the implied warranty of
13*38fd1498Szrj // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14*38fd1498Szrj // General Public License for more details.
15*38fd1498Szrj 
16*38fd1498Szrj // Under Section 7 of GPL version 3, you are granted additional
17*38fd1498Szrj // permissions described in the GCC Runtime Library Exception, version
18*38fd1498Szrj // 3.1, as published by the Free Software Foundation.
19*38fd1498Szrj 
20*38fd1498Szrj // You should have received a copy of the GNU General Public License and
21*38fd1498Szrj // a copy of the GCC Runtime Library Exception along with this program;
22*38fd1498Szrj // see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23*38fd1498Szrj // <http://www.gnu.org/licenses/>.
24*38fd1498Szrj 
25*38fd1498Szrj /** @file parallel/equally_split.h
26*38fd1498Szrj  *  This file is a GNU parallel extension to the Standard C++ Library.
27*38fd1498Szrj  */
28*38fd1498Szrj 
29*38fd1498Szrj // Written by Johannes Singler.
30*38fd1498Szrj 
31*38fd1498Szrj #ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H
32*38fd1498Szrj #define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1
33*38fd1498Szrj 
34*38fd1498Szrj namespace __gnu_parallel
35*38fd1498Szrj {
36*38fd1498Szrj   /** @brief function to split a sequence into parts of almost equal size.
37*38fd1498Szrj    *
38*38fd1498Szrj    *  The resulting sequence __s of length __num_threads+1 contains the
39*38fd1498Szrj    *  splitting positions when splitting the range [0,__n) into parts of
40*38fd1498Szrj    *  almost equal size (plus minus 1).  The first entry is 0, the last
41*38fd1498Szrj    *  one n. There may result empty parts.
42*38fd1498Szrj    *  @param __n Number of elements
43*38fd1498Szrj    *  @param __num_threads Number of parts
44*38fd1498Szrj    *  @param __s Splitters
45*38fd1498Szrj    *  @returns End of __splitter sequence, i.e. @c __s+__num_threads+1 */
46*38fd1498Szrj   template<typename _DifferenceType, typename _OutputIterator>
47*38fd1498Szrj     _OutputIterator
__equally_split(_DifferenceType __n,_ThreadIndex __num_threads,_OutputIterator __s)48*38fd1498Szrj     __equally_split(_DifferenceType __n, _ThreadIndex __num_threads,
49*38fd1498Szrj 		    _OutputIterator __s)
50*38fd1498Szrj     {
51*38fd1498Szrj       _DifferenceType __chunk_length = __n / __num_threads;
52*38fd1498Szrj       _DifferenceType __num_longer_chunks = __n % __num_threads;
53*38fd1498Szrj       _DifferenceType __pos = 0;
54*38fd1498Szrj       for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
55*38fd1498Szrj 	{
56*38fd1498Szrj 	  *__s++ = __pos;
57*38fd1498Szrj 	  __pos += ((__i < __num_longer_chunks)
58*38fd1498Szrj 		    ? (__chunk_length + 1) : __chunk_length);
59*38fd1498Szrj 	}
60*38fd1498Szrj       *__s++ = __n;
61*38fd1498Szrj       return __s;
62*38fd1498Szrj     }
63*38fd1498Szrj 
64*38fd1498Szrj   /** @brief function to split a sequence into parts of almost equal size.
65*38fd1498Szrj    *
66*38fd1498Szrj    *  Returns the position of the splitting point between
67*38fd1498Szrj    *  thread number __thread_no (included) and
68*38fd1498Szrj    *  thread number __thread_no+1 (excluded).
69*38fd1498Szrj    *  @param __n Number of elements
70*38fd1498Szrj    *  @param __num_threads Number of parts
71*38fd1498Szrj    *  @param __thread_no Number of threads
72*38fd1498Szrj    *  @returns splitting point */
73*38fd1498Szrj   template<typename _DifferenceType>
74*38fd1498Szrj     _DifferenceType
__equally_split_point(_DifferenceType __n,_ThreadIndex __num_threads,_ThreadIndex __thread_no)75*38fd1498Szrj     __equally_split_point(_DifferenceType __n,
76*38fd1498Szrj 			  _ThreadIndex __num_threads,
77*38fd1498Szrj 			  _ThreadIndex __thread_no)
78*38fd1498Szrj     {
79*38fd1498Szrj       _DifferenceType __chunk_length = __n / __num_threads;
80*38fd1498Szrj       _DifferenceType __num_longer_chunks = __n % __num_threads;
81*38fd1498Szrj       if (__thread_no < __num_longer_chunks)
82*38fd1498Szrj 	return __thread_no * (__chunk_length + 1);
83*38fd1498Szrj       else
84*38fd1498Szrj 	return __num_longer_chunks * (__chunk_length + 1)
85*38fd1498Szrj           + (__thread_no - __num_longer_chunks) * __chunk_length;
86*38fd1498Szrj     }
87*38fd1498Szrj }
88*38fd1498Szrj 
89*38fd1498Szrj #endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */
90