1// -*- C++ -*-
2
3// Copyright (C) 2007, 2008, 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/par_loop.h
26 *  @brief Parallelization of embarrassingly parallel execution by
27 *  means of equal splitting.
28 *  This file is a GNU parallel extension to the Standard C++ Library.
29 */
30
31// Written by Felix Putze.
32
33#ifndef _GLIBCXX_PARALLEL_PAR_LOOP_H
34#define _GLIBCXX_PARALLEL_PAR_LOOP_H 1
35
36#include <omp.h>
37#include <parallel/settings.h>
38#include <parallel/base.h>
39#include <parallel/equally_split.h>
40
41namespace __gnu_parallel
42{
43  /** @brief Embarrassingly parallel algorithm for random access
44   * iterators, using hand-crafted parallelization by equal splitting
45   * the work.
46   *
47   *  @param __begin Begin iterator of element sequence.
48   *  @param __end End iterator of element sequence.
49   *  @param __o User-supplied functor (comparator, predicate, adding
50   *  functor, ...)
51   *  @param __f Functor to "process" an element with __op (depends on
52   *  desired functionality, e. g. for std::for_each(), ...).
53   *  @param __r Functor to "add" a single __result to the already
54   *  processed elements (depends on functionality).
55   *  @param __base Base value for reduction.
56   *  @param __output Pointer to position where final result is written to
57   *  @param __bound Maximum number of elements processed (e. g. for
58   *  std::count_n()).
59   *  @return User-supplied functor (that may contain a part of the result).
60   */
61  template<typename _RAIter,
62	   typename _Op,
63	   typename _Fu,
64	   typename _Red,
65	   typename _Result>
66    _Op
67    __for_each_template_random_access_ed(_RAIter __begin, _RAIter __end,
68					 _Op __o, _Fu& __f, _Red __r,
69					 _Result __base, _Result& __output,
70      typename std::iterator_traits<_RAIter>::difference_type __bound)
71    {
72      typedef std::iterator_traits<_RAIter> _TraitsType;
73      typedef typename _TraitsType::difference_type _DifferenceType;
74      const _DifferenceType __length = __end - __begin;
75      _Result *__thread_results;
76      bool* __constructed;
77
78      _ThreadIndex __num_threads = __gnu_parallel::min<_DifferenceType>
79	(__get_max_threads(), __length);
80
81#     pragma omp parallel num_threads(__num_threads)
82      {
83#       pragma omp single
84	{
85	  __num_threads = omp_get_num_threads();
86	  __thread_results = static_cast<_Result*>
87	    (::operator new(__num_threads * sizeof(_Result)));
88	  __constructed = new bool[__num_threads];
89	}
90
91	_ThreadIndex __iam = omp_get_thread_num();
92
93	// Neutral element.
94	_Result* __reduct = static_cast<_Result*>
95	  (::operator new(sizeof(_Result)));
96
97	_DifferenceType
98	  __start = equally_split_point(__length, __num_threads, __iam),
99	  __stop = equally_split_point(__length, __num_threads, __iam + 1);
100
101	if (__start < __stop)
102	  {
103	    new(__reduct) _Result(__f(__o, __begin + __start));
104	    ++__start;
105	    __constructed[__iam] = true;
106	  }
107	else
108	  __constructed[__iam] = false;
109
110	for (; __start < __stop; ++__start)
111	  *__reduct = __r(*__reduct, __f(__o, __begin + __start));
112
113	__thread_results[__iam] = *__reduct;
114      } //parallel
115
116      for (_ThreadIndex __i = 0; __i < __num_threads; ++__i)
117	if (__constructed[__i])
118	  __output = __r(__output, __thread_results[__i]);
119
120      // Points to last element processed (needed as return value for
121      // some algorithms like transform).
122      __f._M_finish_iterator = __begin + __length;
123
124      delete[] __thread_results;
125      delete[] __constructed;
126
127      return __o;
128    }
129
130} // end namespace
131
132#endif /* _GLIBCXX_PARALLEL_PAR_LOOP_H */
133