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 RandomAccessIterator, typename _DifferenceTp> 51 void 52 calc_borders(RandomAccessIterator elements, _DifferenceTp length, 53 _DifferenceTp* off) 54 { 55 typedef _DifferenceTp difference_type; 56 57 off[0] = -1; 58 if (length > 1) 59 off[1] = 0; 60 difference_type k = 0; 61 for (difference_type 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 _RandomAccessIterator1, 79 typename _RandomAccessIterator2, 80 typename Pred> 81 _RandomAccessIterator1 82 search_template(_RandomAccessIterator1 begin1, _RandomAccessIterator1 end1, 83 _RandomAccessIterator2 begin2, _RandomAccessIterator2 end2, 84 Pred pred) 85 { 86 typedef std::iterator_traits<_RandomAccessIterator1> traits_type; 87 typedef typename traits_type::difference_type difference_type; 88 89 _GLIBCXX_CALL((end1 - begin1) + (end2 - begin2)); 90 91 difference_type 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 difference_type input_length = (end1 - begin1) - pattern_length; 99 100 // Where is first occurrence of pattern? defaults to end. 101 difference_type result = (end1 - begin1); 102 difference_type *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 thread_index_t num_threads = 112 std::max<difference_type>(1, 113 std::min<difference_type>(input_length, get_max_threads())); 114 115 difference_type 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 difference_type[num_threads + 1]; 124 equally_split(input_length, num_threads, splitters); 125 } 126 127 thread_index_t iam = omp_get_thread_num(); 128 129 difference_type start = splitters[iam], stop = splitters[iam + 1]; 130 131 difference_type pos_in_pattern = 0; 132 bool found_pattern = false; 133 134 while (start <= stop && !found_pattern) 135 { 136 // Get new value of result. 137 #pragma omp flush(result) 138 // No chance for this thread to find first occurrence. 139 if (result < start) 140 break; 141 while (pred(begin1[start + pos_in_pattern], 142 begin2[pos_in_pattern])) 143 { 144 ++pos_in_pattern; 145 if (pos_in_pattern == pattern_length) 146 { 147 // Found new candidate for result. 148 omp_set_lock(&result_lock); 149 result = std::min(result, start); 150 omp_unset_lock(&result_lock); 151 152 found_pattern = true; 153 break; 154 } 155 } 156 // Make safe jump. 157 start += (pos_in_pattern - advances[pos_in_pattern]); 158 pos_in_pattern = 159 (advances[pos_in_pattern] < 0) ? 0 : advances[pos_in_pattern]; 160 } 161 } //parallel 162 163 omp_destroy_lock(&result_lock); 164 165 delete[] splitters; 166 167 // Return iterator on found element. 168 return (begin1 + result); 169 } 170 } // end namespace 171 172 #endif /* _GLIBCXX_PARALLEL_SEARCH_H */ 173
