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
34namespace __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