libstdc++-v3/include/parallel/search.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/search.h
  26  *  @brief Parallel implementation __base for std::search() and
  27  *  std::search_n().
  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_SEARCH_H
  34 #define _GLIBCXX_PARALLEL_SEARCH_H 1
  35
  36 #include <bits/stl_algobase.h>
  37
  38 #include <parallel/parallel.h>
  39 #include <parallel/equally_split.h>
  40
  41
  42 namespace __gnu_parallel
  43 {
  44   /**
  45    *  @brief Precalculate __advances for Knuth-Morris-Pratt algorithm.
  46    *  @param __elements Begin iterator of sequence to search for.
  47    *  @param __length Length of sequence to search for.
  48    *  @param __advances Returned __offsets.
  49    */
  50 template<typename _RAIter, typename _DifferenceTp>
  51   void
  52   __calc_borders(_RAIter __elements, _DifferenceTp __length,
  53               _DifferenceTp* __off)
  54   {
  55     typedef _DifferenceTp _DifferenceType;
  56
  57     __off[0] = -1;
  58     if (__length > 1)
  59       __off[1] = 0;
  60     _DifferenceType __k = 0;
  61     for (_DifferenceType __j = 2; __j <= __length; __j++)
  62       {
  63         while ((__k >= 0) && !(__elements[__k] == __elements[__j-1]))
  64           __k = __off[__k];
  65         __off[__j] = ++__k;
  66       }
  67   }
  68
  69   // Generic parallel find algorithm (requires random access iterator).
  70
  71   /** @brief Parallel std::search.
  72    *  @param __begin1 Begin iterator of first sequence.
  73    *  @param __end1 End iterator of first sequence.
  74    *  @param __begin2 Begin iterator of second sequence.
  75    *  @param __end2 End iterator of second sequence.
  76    *  @param __pred Find predicate.
  77    *  @return Place of finding in first sequences. */
  78 template<typename __RAIter1,
  79          typename __RAIter2,
  80          typename _Pred>
  81   __RAIter1
  82   __search_template(__RAIter1 __begin1, __RAIter1 __end1,
  83                   __RAIter2 __begin2, __RAIter2 __end2,
  84                   _Pred __pred)
  85   {
  86     typedef std::iterator_traits<__RAIter1> _TraitsType;
  87     typedef typename _TraitsType::difference_type _DifferenceType;
  88
  89     _GLIBCXX_CALL((__end1 - __begin1) + (__end2 - __begin2));
  90
  91     _DifferenceType __pattern_length = __end2 - __begin2;
  92
  93     // Pattern too short.
  94     if(__pattern_length <= 0)
  95       return __end1;
  96
  97     // Last point to start search.
  98     _DifferenceType __input_length = (__end1 - __begin1) - __pattern_length;
  99
 100     // Where is first occurrence of pattern? defaults to end.
 101     _DifferenceType __result = (__end1 - __begin1);
 102     _DifferenceType *__splitters;
 103
 104     // Pattern too long.
 105     if (__input_length < 0)
 106       return __end1;
 107
 108     omp_lock_t __result_lock;
 109     omp_init_lock(&__result_lock);
 110
 111     _ThreadIndex __num_threads =
 112         std::max<_DifferenceType>(1,
 113             std::min<_DifferenceType>(__input_length, __get_max_threads()));
 114
 115     _DifferenceType __advances[__pattern_length];
 116     __calc_borders(__begin2, __pattern_length, __advances);
 117
 118 #   pragma omp parallel num_threads(__num_threads)
 119       {
 120 #       pragma omp single
 121           {
 122             __num_threads = omp_get_num_threads();
 123             __splitters = new _DifferenceType[__num_threads + 1];
 124             equally_split(__input_length, __num_threads, __splitters);
 125           }
 126
 127         _ThreadIndex __iam = omp_get_thread_num();
 128
 129         _DifferenceType __start = __splitters[__iam],
 130                         __stop = __splitters[__iam + 1];
 131
 132         _DifferenceType __pos_in_pattern = 0;
 133         bool __found_pattern = false;
 134
 135         while (__start <= __stop && !__found_pattern)
 136           {
 137             // Get new value of result.
 138             #pragma omp flush(__result)
 139             // No chance for this thread to find first occurrence.
 140             if (__result < __start)
 141               break;
 142             while (__pred(__begin1[__start + __pos_in_pattern],
 143                          __begin2[__pos_in_pattern]))
 144               {
 145                 ++__pos_in_pattern;
 146                 if (__pos_in_pattern == __pattern_length)
 147                   {
 148                     // Found new candidate for result.
 149                             omp_set_lock(&__result_lock);
 150                     __result = std::min(__result, __start);
 151                             omp_unset_lock(&__result_lock);
 152
 153                     __found_pattern = true;
 154                     break;
 155                   }
 156               }
 157             // Make safe jump.
 158             __start += (__pos_in_pattern - __advances[__pos_in_pattern]);
 159             __pos_in_pattern =
 160                 (__advances[__pos_in_pattern] < 0) ?
 161                   0 : __advances[__pos_in_pattern];
 162           }
 163       } //parallel
 164
 165     omp_destroy_lock(&__result_lock);
 166
 167     delete[] __splitters;
 168
 169     // Return iterator on found element.
 170     return (__begin1 + __result);
 171   }
 172 } // end namespace
 173
 174 #endif /* _GLIBCXX_PARALLEL_SEARCH_H */