libstdc++
search.h
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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 
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22 // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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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 __advances 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 */