3 // Copyright (C) 2007, 2008 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 2, or (at your option) any later
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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 // You should have received a copy of the GNU General Public License
17 // along with this library; see the file COPYING. If not, write to
18 // the Free Software Foundation, 59 Temple Place - Suite 330, Boston,
19 // MA 02111-1307, USA.
21 // As a special exception, you may use this file as part of a free
22 // software library without restriction. Specifically, if other files
23 // instantiate templates or use macros or inline functions from this
24 // file, or you compile this file and link it with other files to
25 // produce an executable, this file does not by itself cause the
26 // resulting executable to be covered by the GNU General Public
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31 /** @file parallel/search.h
32 * @brief Parallel implementation base for std::search() and
34 * This file is a GNU parallel extension to the Standard C++ Library.
37 // Written by Felix Putze.
39 #ifndef _GLIBCXX_PARALLEL_SEARCH_H
40 #define _GLIBCXX_PARALLEL_SEARCH_H 1
42 #include <bits/stl_algobase.h>
44 #include <parallel/parallel.h>
45 #include <parallel/equally_split.h>
48 namespace __gnu_parallel
51 * @brief Precalculate advances for Knuth-Morris-Pratt algorithm.
52 * @param elements Begin iterator of sequence to search for.
53 * @param length Length of sequence to search for.
54 * @param advances Returned offsets.
56 template<typename RandomAccessIterator
, typename _DifferenceTp
>
58 calc_borders(RandomAccessIterator elements
, _DifferenceTp length
,
61 typedef _DifferenceTp difference_type
;
66 difference_type k
= 0;
67 for (difference_type j
= 2; j
<= length
; j
++)
69 while ((k
>= 0) && !(elements
[k
] == elements
[j
-1]))
75 // Generic parallel find algorithm (requires random access iterator).
77 /** @brief Parallel std::search.
78 * @param begin1 Begin iterator of first sequence.
79 * @param end1 End iterator of first sequence.
80 * @param begin2 Begin iterator of second sequence.
81 * @param end2 End iterator of second sequence.
82 * @param pred Find predicate.
83 * @return Place of finding in first sequences. */
84 template<typename _RandomAccessIterator1
,
85 typename _RandomAccessIterator2
,
87 _RandomAccessIterator1
88 search_template(_RandomAccessIterator1 begin1
, _RandomAccessIterator1 end1
,
89 _RandomAccessIterator2 begin2
, _RandomAccessIterator2 end2
,
92 typedef std::iterator_traits
<_RandomAccessIterator1
> traits_type
;
93 typedef typename
traits_type::difference_type difference_type
;
95 _GLIBCXX_CALL((end1
- begin1
) + (end2
- begin2
));
97 difference_type pattern_length
= end2
- begin2
;
100 if(pattern_length
<= 0)
103 // Last point to start search.
104 difference_type input_length
= (end1
- begin1
) - pattern_length
;
106 // Where is first occurrence of pattern? defaults to end.
107 difference_type result
= (end1
- begin1
);
108 difference_type
*splitters
;
111 if (input_length
< 0)
114 omp_lock_t result_lock
;
115 omp_init_lock(&result_lock
);
117 thread_index_t num_threads
=
118 std::max
<difference_type
>(1,
119 std::min
<difference_type
>(input_length
, get_max_threads()));
121 difference_type advances
[pattern_length
];
122 calc_borders(begin2
, pattern_length
, advances
);
124 # pragma omp parallel num_threads(num_threads)
128 num_threads
= omp_get_num_threads();
129 splitters
= new difference_type
[num_threads
+ 1];
130 equally_split(input_length
, num_threads
, splitters
);
133 thread_index_t iam
= omp_get_thread_num();
135 difference_type start
= splitters
[iam
], stop
= splitters
[iam
+ 1];
137 difference_type pos_in_pattern
= 0;
138 bool found_pattern
= false;
140 while (start
<= stop
&& !found_pattern
)
142 // Get new value of result.
143 #pragma omp flush(result)
144 // No chance for this thread to find first occurrence.
147 while (pred(begin1
[start
+ pos_in_pattern
],
148 begin2
[pos_in_pattern
]))
151 if (pos_in_pattern
== pattern_length
)
153 // Found new candidate for result.
154 omp_set_lock(&result_lock
);
155 result
= std::min(result
, start
);
156 omp_unset_lock(&result_lock
);
158 found_pattern
= true;
163 start
+= (pos_in_pattern
- advances
[pos_in_pattern
]);
165 (advances
[pos_in_pattern
] < 0) ? 0 : advances
[pos_in_pattern
];
169 omp_destroy_lock(&result_lock
);
173 // Return iterator on found element.
174 return (begin1
+ result
);