contrib/gcc-4.4/libstdc++-v3/include/parallel/quicksort.h

   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/quicksort.h
  26  *  @brief Implementation of a unbalanced parallel quicksort (in-place).
  27  *  This file is a GNU parallel extension to the Standard C++ Library.
  28  */
  29
  30 // Written by Johannes Singler.
  31
  32 #ifndef _GLIBCXX_PARALLEL_QUICKSORT_H
  33 #define _GLIBCXX_PARALLEL_QUICKSORT_H 1
  34
  35 #include <parallel/parallel.h>
  36 #include <parallel/partition.h>
  37
  38 namespace __gnu_parallel
  39 {
  40   /** @brief Unbalanced quicksort divide step.
  41    *  @param begin Begin iterator of subsequence.
  42    *  @param end End iterator of subsequence.
  43    *  @param comp Comparator.
  44    *  @param pivot_rank Desired rank of the pivot.
  45    *  @param num_samples Choose pivot from that many samples.
  46    *  @param num_threads Number of threads that are allowed to work on
  47    *  this part.
  48    */
  49   template<typename RandomAccessIterator, typename Comparator>
  50     typename std::iterator_traits<RandomAccessIterator>::difference_type
  51     parallel_sort_qs_divide(RandomAccessIterator begin,
  52                             RandomAccessIterator end,
  53                             Comparator comp, typename std::iterator_traits
  54                             <RandomAccessIterator>::difference_type pivot_rank,
  55                             typename std::iterator_traits
  56                             <RandomAccessIterator>::difference_type
  57                             num_samples, thread_index_t num_threads)
  58     {
  59       typedef std::iterator_traits<RandomAccessIterator> traits_type;
  60       typedef typename traits_type::value_type value_type;
  61       typedef typename traits_type::difference_type difference_type;
  62
  63       difference_type n = end - begin;
  64       num_samples = std::min(num_samples, n);
  65
  66       // Allocate uninitialized, to avoid default constructor.
  67       value_type* samples =
  68         static_cast<value_type*>(::operator new(num_samples
  69                                                 * sizeof(value_type)));
  70
  71       for (difference_type s = 0; s < num_samples; ++s)
  72         {
  73           const unsigned long long index = static_cast<unsigned long long>(s)
  74             * n / num_samples;
  75           ::new(&(samples[s])) value_type(begin[index]);
  76         }
  77
  78       __gnu_sequential::sort(samples, samples + num_samples, comp);
  79
  80       value_type& pivot = samples[pivot_rank * num_samples / n];
  81
  82       __gnu_parallel::binder2nd<Comparator, value_type, value_type, bool>
  83         pred(comp, pivot);
  84       difference_type split =
  85           parallel_partition(begin, end, pred, num_threads);
  86
  87       ::operator delete(samples);
  88
  89       return split;
  90     }
  91
  92   /** @brief Unbalanced quicksort conquer step.
  93    *  @param begin Begin iterator of subsequence.
  94    *  @param end End iterator of subsequence.
  95    *  @param comp Comparator.
  96    *  @param num_threads Number of threads that are allowed to work on
  97    *  this part.
  98    */
  99   template<typename RandomAccessIterator, typename Comparator>
 100     void
 101     parallel_sort_qs_conquer(RandomAccessIterator begin,
 102                              RandomAccessIterator end,
 103                              Comparator comp,
 104                              thread_index_t num_threads)
 105     {
 106       typedef std::iterator_traits<RandomAccessIterator> traits_type;
 107       typedef typename traits_type::value_type value_type;
 108       typedef typename traits_type::difference_type difference_type;
 109
 110       if (num_threads <= 1)
 111         {
 112           __gnu_sequential::sort(begin, end, comp);
 113           return;
 114         }
 115
 116       difference_type n = end - begin, pivot_rank;
 117
 118       if (n <= 1)
 119         return;
 120
 121       thread_index_t num_threads_left;
 122
 123       if ((num_threads % 2) == 1)
 124         num_threads_left = num_threads / 2 + 1;
 125       else
 126         num_threads_left = num_threads / 2;
 127
 128       pivot_rank = n * num_threads_left / num_threads;
 129
 130       difference_type split =
 131         parallel_sort_qs_divide(begin, end, comp, pivot_rank,
 132                                 _Settings::get().sort_qs_num_samples_preset,
 133                                 num_threads);
 134
 135 #pragma omp parallel sections num_threads(2)
 136       {
 137 #pragma omp section
 138         parallel_sort_qs_conquer(begin, begin + split,
 139                                  comp, num_threads_left);
 140 #pragma omp section
 141         parallel_sort_qs_conquer(begin + split, end,
 142                                  comp, num_threads - num_threads_left);
 143       }
 144     }
 145
 146
 147
 148   /** @brief Unbalanced quicksort main call.
 149    *  @param begin Begin iterator of input sequence.
 150    *  @param end End iterator input sequence, ignored.
 151    *  @param comp Comparator.
 152    *  @param num_threads Number of threads that are allowed to work on
 153    *  this part.
 154    */
 155   template<typename RandomAccessIterator, typename Comparator>
 156     void
 157     parallel_sort_qs(RandomAccessIterator begin,
 158                      RandomAccessIterator end,
 159                      Comparator comp,
 160                      thread_index_t num_threads)
 161     {
 162       _GLIBCXX_CALL(n)
 163
 164       typedef std::iterator_traits<RandomAccessIterator> traits_type;
 165       typedef typename traits_type::value_type value_type;
 166       typedef typename traits_type::difference_type difference_type;
 167
 168       difference_type n = end - begin;
 169
 170       // At least one element per processor.
 171       if (num_threads > n)
 172         num_threads = static_cast<thread_index_t>(n);
 173
 174       parallel_sort_qs_conquer(begin, begin + n, comp, num_threads);
 175     }
 176
 177 } //namespace __gnu_parallel
 178
 179 #endif /* _GLIBCXX_PARALLEL_QUICKSORT_H */