3 // Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
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
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.
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.
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/>.
25 /** @file parallel/search.h
26 * @brief Parallel implementation base for std::search() and
28 * This file is a GNU parallel extension to the Standard C++ Library.
31 // Written by Felix Putze.
33 #ifndef _GLIBCXX_PARALLEL_SEARCH_H
34 #define _GLIBCXX_PARALLEL_SEARCH_H 1
36 #include <bits/stl_algobase.h>
38 #include <parallel/parallel.h>
39 #include <parallel/equally_split.h>
42 namespace __gnu_parallel
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.
50 template<typename RandomAccessIterator
, typename _DifferenceTp
>
52 calc_borders(RandomAccessIterator elements
, _DifferenceTp length
,
55 typedef _DifferenceTp difference_type
;
60 difference_type k
= 0;
61 for (difference_type j
= 2; j
<= length
; j
++)
63 while ((k
>= 0) && !(elements
[k
] == elements
[j
-1]))
69 // Generic parallel find algorithm (requires random access iterator).
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
,
81 _RandomAccessIterator1
82 search_template(_RandomAccessIterator1 begin1
, _RandomAccessIterator1 end1
,
83 _RandomAccessIterator2 begin2
, _RandomAccessIterator2 end2
,
86 typedef std::iterator_traits
<_RandomAccessIterator1
> traits_type
;
87 typedef typename
traits_type::difference_type difference_type
;
89 _GLIBCXX_CALL((end1
- begin1
) + (end2
- begin2
));
91 difference_type pattern_length
= end2
- begin2
;
94 if(pattern_length
<= 0)
97 // Last point to start search.
98 difference_type input_length
= (end1
- begin1
) - pattern_length
;
100 // Where is first occurrence of pattern? defaults to end.
101 difference_type result
= (end1
- begin1
);
102 difference_type
*splitters
;
105 if (input_length
< 0)
108 omp_lock_t result_lock
;
109 omp_init_lock(&result_lock
);
111 thread_index_t num_threads
=
112 std::max
<difference_type
>(1,
113 std::min
<difference_type
>(input_length
, get_max_threads()));
115 difference_type advances
[pattern_length
];
116 calc_borders(begin2
, pattern_length
, advances
);
118 # pragma omp parallel num_threads(num_threads)
122 num_threads
= omp_get_num_threads();
123 splitters
= new difference_type
[num_threads
+ 1];
124 equally_split(input_length
, num_threads
, splitters
);
127 thread_index_t iam
= omp_get_thread_num();
129 difference_type start
= splitters
[iam
], stop
= splitters
[iam
+ 1];
131 difference_type pos_in_pattern
= 0;
132 bool found_pattern
= false;
134 while (start
<= stop
&& !found_pattern
)
136 // Get new value of result.
137 #pragma omp flush(result)
138 // No chance for this thread to find first occurrence.
141 while (pred(begin1
[start
+ pos_in_pattern
],
142 begin2
[pos_in_pattern
]))
145 if (pos_in_pattern
== pattern_length
)
147 // Found new candidate for result.
148 omp_set_lock(&result_lock
);
149 result
= std::min(result
, start
);
150 omp_unset_lock(&result_lock
);
152 found_pattern
= true;
157 start
+= (pos_in_pattern
- advances
[pos_in_pattern
]);
159 (advances
[pos_in_pattern
] < 0) ? 0 : advances
[pos_in_pattern
];
163 omp_destroy_lock(&result_lock
);
167 // Return iterator on found element.
168 return (begin1
+ result
);
172 #endif /* _GLIBCXX_PARALLEL_SEARCH_H */