libstdc++-v3/include/parallel/equally_split.h

   1 // -*- C++ -*-
   2
   3 // Copyright (C) 2007 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 2, 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 // You should have received a copy of the GNU General Public License
  17 // along with this library; see the file COPYING.  If not, write to
  18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
  19 // MA 02111-1307, USA.
  20
  21 // As a special exception, you may use this file as part of a free
  22 // software library without restriction.  Specifically, if other files
  23 // instantiate templates or use macros or inline functions from this
  24 // file, or you compile this file and link it with other files to
  25 // produce an executable, this file does not by itself cause the
  26 // resulting executable to be covered by the GNU General Public
  27 // License.  This exception does not however invalidate any other
  28 // reasons why the executable file might be covered by the GNU General
  29 // Public License.
  30
  31 /** @file parallel/equally_split.h
  32  *  This file is a GNU parallel extension to the Standard C++ Library.
  33  */
  34
  35 // Written by Johannes Singler.
  36
  37 #ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H
  38 #define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1
  39
  40 namespace __gnu_parallel
  41 {
  42   /** @brief Function to split a sequence into parts of almost equal size.
  43    *
  44    *  The resulting sequence s of length p+1 contains the splitting
  45    *  positions when splitting the range [0,n) into parts of almost
  46    *  equal size (plus minus 1).  The first entry is 0, the last one
  47    *  n. There may result empty parts.
  48    *  @param n Number of elements
  49    *  @param p Number of parts
  50    *  @param s Splitters
  51    *  @returns End of splitter sequence, i. e. @c s+p+1 */
  52   template<typename _DifferenceTp, typename OutputIterator>
  53   OutputIterator
  54   equally_split(_DifferenceTp n, thread_index_t p, OutputIterator s)
  55   {
  56     typedef _DifferenceTp difference_type;
  57     difference_type chunk_length = n / p, split = n % p, start = 0;
  58     for (int i = 0; i < p; i++)
  59       {
  60         *s++ = start;
  61         start += (difference_type(i) < split) ? (chunk_length + 1) : chunk_length;
  62       }
  63     *s++ = n;
  64     return s;
  65   }
  66 }
  67
  68 #endif