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173 lines
5.3 KiB
C++
173 lines
5.3 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2016 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/search.h
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* @brief Parallel implementation base for std::search() and
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* std::search_n().
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* This file is a GNU parallel extension to the Standard C++ Library.
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*/
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// Written by Felix Putze.
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#ifndef _GLIBCXX_PARALLEL_SEARCH_H
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#define _GLIBCXX_PARALLEL_SEARCH_H 1
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#include <bits/stl_algobase.h>
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#include <parallel/parallel.h>
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#include <parallel/equally_split.h>
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namespace __gnu_parallel
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{
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/**
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* @brief Precalculate __advances for Knuth-Morris-Pratt algorithm.
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* @param __elements Begin iterator of sequence to search for.
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* @param __length Length of sequence to search for.
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* @param __off Returned __offsets.
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*/
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template<typename _RAIter, typename _DifferenceTp>
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void
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__calc_borders(_RAIter __elements, _DifferenceTp __length,
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_DifferenceTp* __off)
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{
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typedef _DifferenceTp _DifferenceType;
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__off[0] = -1;
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if (__length > 1)
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__off[1] = 0;
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_DifferenceType __k = 0;
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for (_DifferenceType __j = 2; __j <= __length; __j++)
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{
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while ((__k >= 0) && !(__elements[__k] == __elements[__j-1]))
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__k = __off[__k];
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__off[__j] = ++__k;
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}
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}
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// Generic parallel find algorithm (requires random access iterator).
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/** @brief Parallel std::search.
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* @param __begin1 Begin iterator of first sequence.
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* @param __end1 End iterator of first sequence.
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* @param __begin2 Begin iterator of second sequence.
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* @param __end2 End iterator of second sequence.
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* @param __pred Find predicate.
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* @return Place of finding in first sequences. */
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template<typename __RAIter1,
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typename __RAIter2,
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typename _Pred>
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__RAIter1
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__search_template(__RAIter1 __begin1, __RAIter1 __end1,
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__RAIter2 __begin2, __RAIter2 __end2,
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_Pred __pred)
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{
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typedef std::iterator_traits<__RAIter1> _TraitsType;
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typedef typename _TraitsType::difference_type _DifferenceType;
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_GLIBCXX_CALL((__end1 - __begin1) + (__end2 - __begin2));
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_DifferenceType __pattern_length = __end2 - __begin2;
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// Pattern too short.
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if(__pattern_length <= 0)
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return __end1;
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// Last point to start search.
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_DifferenceType __input_length = (__end1 - __begin1) - __pattern_length;
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// Where is first occurrence of pattern? defaults to end.
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_DifferenceType __result = (__end1 - __begin1);
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_DifferenceType *__splitters;
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// Pattern too long.
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if (__input_length < 0)
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return __end1;
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omp_lock_t __result_lock;
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omp_init_lock(&__result_lock);
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_ThreadIndex __num_threads = std::max<_DifferenceType>
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(1, std::min<_DifferenceType>(__input_length,
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__get_max_threads()));
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_DifferenceType __advances[__pattern_length];
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__calc_borders(__begin2, __pattern_length, __advances);
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# pragma omp parallel num_threads(__num_threads)
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{
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# pragma omp single
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{
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__num_threads = omp_get_num_threads();
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__splitters = new _DifferenceType[__num_threads + 1];
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__equally_split(__input_length, __num_threads, __splitters);
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}
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_ThreadIndex __iam = omp_get_thread_num();
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_DifferenceType __start = __splitters[__iam],
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__stop = __splitters[__iam + 1];
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_DifferenceType __pos_in_pattern = 0;
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bool __found_pattern = false;
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while (__start <= __stop && !__found_pattern)
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{
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// Get new value of result.
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#pragma omp flush(__result)
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// No chance for this thread to find first occurrence.
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if (__result < __start)
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break;
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while (__pred(__begin1[__start + __pos_in_pattern],
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__begin2[__pos_in_pattern]))
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{
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++__pos_in_pattern;
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if (__pos_in_pattern == __pattern_length)
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{
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// Found new candidate for result.
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omp_set_lock(&__result_lock);
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__result = std::min(__result, __start);
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omp_unset_lock(&__result_lock);
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__found_pattern = true;
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break;
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}
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}
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// Make safe jump.
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__start += (__pos_in_pattern - __advances[__pos_in_pattern]);
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__pos_in_pattern = (__advances[__pos_in_pattern] < 0
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? 0 : __advances[__pos_in_pattern]);
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}
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} //parallel
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omp_destroy_lock(&__result_lock);
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delete[] __splitters;
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// Return iterator on found element.
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return (__begin1 + __result);
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}
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} // end namespace
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#endif /* _GLIBCXX_PARALLEL_SEARCH_H */
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