1 // -*- C++ -*-
2
3 // Copyright (C) 2007-2023 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 */