mingw/lib/gcc/mingw32/4.4.0/include/c++/parallel/equally_split.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007, 2009 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 splitting
  39  *  positions when splitting the range [0,n) into parts of almost
  40  *  equal size (plus minus 1).  The first entry is 0, the last one
  41  *  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 difference_type, typename OutputIterator>
  47   OutputIterator
  48   equally_split(difference_type n, thread_index_t num_threads, OutputIterator s)
  49   {
  50     difference_type chunk_length = n / num_threads;
  51     difference_type num_longer_chunks = n % num_threads;
  52     difference_type pos = 0;
  53     for (thread_index_t i = 0; i < num_threads; ++i)
  54       {
  55         *s++ = pos;
  56         pos += (i < num_longer_chunks) ? (chunk_length + 1) : chunk_length;
  57       }
  58     *s++ = n;
  59     return s;
  60   }
  61
  62
  63 /** @brief Function to split a sequence into parts of almost equal size.
  64  *
  65  *  Returns the position of the splitting point between
  66  *  thread number thread_no (included) and
  67  *  thread number thread_no+1 (excluded).
  68  *  @param n Number of elements
  69  *  @param num_threads Number of parts
  70  *  @returns _SplittingAlgorithm point */
  71 template<typename difference_type>
  72   difference_type
  73   equally_split_point(difference_type n,
  74                       thread_index_t num_threads,
  75                       thread_index_t thread_no)
  76   {
  77     difference_type chunk_length = n / num_threads;
  78     difference_type num_longer_chunks = n % num_threads;
  79     if (thread_no < num_longer_chunks)
  80       return thread_no * (chunk_length + 1);
  81     else
  82       return num_longer_chunks * (chunk_length + 1)
  83           + (thread_no - num_longer_chunks) * chunk_length;
  84   }
  85 }
  86
  87 #endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */