1 // -*- C++ -*-
2 
3 // Copyright (C) 2007-2020 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
__calc_borders(_RAIter __elements,_DifferenceTp __length,_DifferenceTp * __off)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
__search_template(__RAIter1 __begin1,__RAIter1 __end1,__RAIter2 __begin2,__RAIter2 __end2,_Pred __pred)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