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// -*- C++ -*-

// Copyright (C) 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the terms

// of the GNU General Public License as published by the Free Software

// Foundation; either version 3, or (at your option) any later

// version.

// This library is distributed in the hope that it will be useful, but

// WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

// General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// <http://www.gnu.org/licenses/>.

/** @file parallel/equally_split.h

 *  This file is a GNU parallel extension to the Standard C++ Library.

 */

// Written by Johannes Singler.

#ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H

#define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1

namespace __gnu_parallel

{

  /** @brief function to split a sequence into parts of almost equal size.

   *

   *  The resulting sequence __s of length __num_threads+1 contains the

   *  splitting positions when splitting the range [0,__n) into parts of

   *  almost equal size (plus minus 1).  The first entry is 0, the last

   *  one n. There may result empty parts.

   *  @param __n Number of elements

   *  @param __num_threads Number of parts

   *  @param __s Splitters

   *  @returns End of __splitter sequence, i.e. @c __s+__num_threads+1 */

  template<typename _DifferenceType, typename _OutputIterator>

    _OutputIterator

    __equally_split(_DifferenceType __n, _ThreadIndex __num_threads,

                    _OutputIterator __s)

    {

      _DifferenceType __chunk_length = __n / __num_threads;

      _DifferenceType __num_longer_chunks = __n % __num_threads;

      _DifferenceType __pos = 0;

      for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)

        {

          *__s++ = __pos;

          __pos += ((__i < __num_longer_chunks)

                    ? (__chunk_length + 1) : __chunk_length);

        }

      *__s++ = __n;

      return __s;

    }

  /** @brief function to split a sequence into parts of almost equal size.

   *

   *  Returns the position of the splitting point between

   *  thread number __thread_no (included) and

   *  thread number __thread_no+1 (excluded).

   *  @param __n Number of elements

   *  @param __num_threads Number of parts

   *  @param __thread_no Number of threads

   *  @returns splitting point */

  template<typename _DifferenceType>

    _DifferenceType

    __equally_split_point(_DifferenceType __n,

                          _ThreadIndex __num_threads,

                          _ThreadIndex __thread_no)

    {

      _DifferenceType __chunk_length = __n / __num_threads;

      _DifferenceType __num_longer_chunks = __n % __num_threads;

      if (__thread_no < __num_longer_chunks)

        return __thread_no * (__chunk_length + 1);

      else

        return __num_longer_chunks * (__chunk_length + 1)

          + (__thread_no - __num_longer_chunks) * __chunk_length;

    }

}

#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */