1 // -*- C++ -*- 2 3 // Copyright (C) 2007-2018 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 namespace __gnu_parallel 42 { 43 /** 44 * @brief Precalculate __advances for Knuth-Morris-Pratt algorithm. 45 * @param __elements Begin iterator of sequence to search for. 46 * @param __length Length of sequence to search for. 47 * @param __off Returned __offsets. 48 */ 49 template<typename _RAIter, typename _DifferenceTp> 50 void 51 __calc_borders(_RAIter __elements, _DifferenceTp __length, 52 _DifferenceTp* __off) 53 { 54 typedef _DifferenceTp _DifferenceType; 55 56 __off[0] = -1; 57 if (__length > 1) 58 __off[1] = 0; 59 _DifferenceType __k = 0; 60 for (_DifferenceType __j = 2; __j <= __length; __j++) 61 { 62 while ((__k >= 0) && !(__elements[__k] == __elements[__j-1])) 63 __k = __off[__k]; 64 __off[__j] = ++__k; 65 } 66 } 67 68 // Generic parallel find algorithm (requires random access iterator). 69 70 /** @brief Parallel std::search. 71 * @param __begin1 Begin iterator of first sequence. 72 * @param __end1 End iterator of first sequence. 73 * @param __begin2 Begin iterator of second sequence. 74 * @param __end2 End iterator of second sequence. 75 * @param __pred Find predicate. 76 * @return Place of finding in first sequences. */ 77 template<typename __RAIter1, 78 typename __RAIter2, 79 typename _Pred> 80 __RAIter1 81 __search_template(__RAIter1 __begin1, __RAIter1 __end1, 82 __RAIter2 __begin2, __RAIter2 __end2, 83 _Pred __pred) 84 { 85 typedef std::iterator_traits<__RAIter1> _TraitsType; 86 typedef typename _TraitsType::difference_type _DifferenceType; 87 88 _GLIBCXX_CALL((__end1 - __begin1) + (__end2 - __begin2)); 89 90 _DifferenceType __pattern_length = __end2 - __begin2; 91 92 // Pattern too short. 93 if(__pattern_length <= 0) 94 return __end1; 95 96 // Last point to start search. 97 _DifferenceType __input_length = (__end1 - __begin1) - __pattern_length; 98 99 // Where is first occurrence of pattern? defaults to end. 100 _DifferenceType __result = (__end1 - __begin1); 101 _DifferenceType *__splitters; 102 103 // Pattern too long. 104 if (__input_length < 0) 105 return __end1; 106 107 omp_lock_t __result_lock; 108 omp_init_lock(&__result_lock); 109 110 _ThreadIndex __num_threads = std::max<_DifferenceType> 111 (1, std::min<_DifferenceType>(__input_length, 112 __get_max_threads())); 113 114 _DifferenceType __advances[__pattern_length]; 115 __calc_borders(__begin2, __pattern_length, __advances); 116 117 # pragma omp parallel num_threads(__num_threads) 118 { 119 # pragma omp single 120 { 121 __num_threads = omp_get_num_threads(); 122 __splitters = new _DifferenceType[__num_threads + 1]; 123 __equally_split(__input_length, __num_threads, __splitters); 124 } 125 126 _ThreadIndex __iam = omp_get_thread_num(); 127 128 _DifferenceType __start = __splitters[__iam], 129 __stop = __splitters[__iam + 1]; 130 131 _DifferenceType __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 = (__advances[__pos_in_pattern] < 0 159 ? 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