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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/par_loop.h

 *  @brief Parallelization of embarrassingly parallel execution by

 *  means of equal splitting.

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

 */

// Written by Felix Putze.

#ifndef _GLIBCXX_PARALLEL_PAR_LOOP_H

#define _GLIBCXX_PARALLEL_PAR_LOOP_H 1

#include <omp.h>

#include <parallel/settings.h>

#include <parallel/base.h>

#include <parallel/equally_split.h>

namespace __gnu_parallel

{

  /** @brief Embarrassingly parallel algorithm for random access

   * iterators, using hand-crafted parallelization by equal splitting

   * the work.

   *

   *  @param __begin Begin iterator of element sequence.

   *  @param __end End iterator of element sequence.

   *  @param __o User-supplied functor (comparator, predicate, adding

   *  functor, ...)

   *  @param __f Functor to "process" an element with __op (depends on

   *  desired functionality, e. g. for std::for_each(), ...).

   *  @param __r Functor to "add" a single __result to the already

   *  processed elements (depends on functionality).

   *  @param __base Base value for reduction.

   *  @param __output Pointer to position where final result is written to

   *  @param __bound Maximum number of elements processed (e. g. for

   *  std::count_n()).

   *  @return User-supplied functor (that may contain a part of the result).

   */

  template<typename _RAIter,

           typename _Op,

           typename _Fu,

           typename _Red,

           typename _Result>

    _Op

    __for_each_template_random_access_ed(_RAIter __begin, _RAIter __end,

                                         _Op __o, _Fu& __f, _Red __r,

                                         _Result __base, _Result& __output,

      typename std::iterator_traits<_RAIter>::difference_type __bound)

    {

      typedef std::iterator_traits<_RAIter> _TraitsType;

      typedef typename _TraitsType::difference_type _DifferenceType;

      const _DifferenceType __length = __end - __begin;

      _Result *__thread_results;

      bool* __constructed;

      _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>

        (__get_max_threads(), __length);

#     pragma omp parallel num_threads(__num_threads)

      {

#       pragma omp single

        {

          __num_threads = omp_get_num_threads();

          __thread_results = static_cast<_Result*>

            (::operator new(__num_threads * sizeof(_Result)));

          __constructed = new bool[__num_threads];

        }

        _ThreadIndex __iam = omp_get_thread_num();

        // Neutral element.

        _Result* __reduct;

        _DifferenceType

          __start = __equally_split_point(__length, __num_threads, __iam),

          __stop = __equally_split_point(__length, __num_threads, __iam + 1);

        if (__start < __stop)

          {

            __reduct = new _Result(__f(__o, __begin + __start));

            ++__start;

            __constructed[__iam] = true;

          }

        else

          __constructed[__iam] = false;

        for (; __start < __stop; ++__start)

          *__reduct = __r(*__reduct, __f(__o, __begin + __start));

        if (__constructed[__iam])

          {

            ::new(&__thread_results[__iam]) _Result(*__reduct);

            delete __reduct;

          }

      } //parallel

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

        if (__constructed[__i])

          {

            __output = __r(__output, __thread_results[__i]);

            __thread_results[__i].~_Result();

          }

      // Points to last element processed (needed as return value for

      // some algorithms like transform).

      __f._M_finish_iterator = __begin + __length;

      ::operator delete(__thread_results);

      delete[] __constructed;

      return __o;

    }

} // end namespace

#endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */