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
41namespace __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 */
173