search.h
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// -*- C++ -*-
// Copyright (C) 2007-2013 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the terms
// of the GNU General Public License as published by the Free Software
// Foundation; either version 3, or (at your option) any later
// version.
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// General Public License for more details.
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.
/** @file parallel/search.h
* @brief Parallel implementation base for std::search() and
* std::search_n().
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Felix Putze.
#ifndef _GLIBCXX_PARALLEL_SEARCH_H
#define _GLIBCXX_PARALLEL_SEARCH_H 1
#include <bits/stl_algobase.h>
#include <parallel/parallel.h>
#include <parallel/equally_split.h>
namespace __gnu_parallel
{
/**
* @brief Precalculate __advances for Knuth-Morris-Pratt algorithm.
* @param __elements Begin iterator of sequence to search for.
* @param __length Length of sequence to search for.
* @param __off Returned __offsets.
*/
template<typename _RAIter, typename _DifferenceTp>
void
__calc_borders(_RAIter __elements, _DifferenceTp __length,
_DifferenceTp* __off)
{
typedef _DifferenceTp _DifferenceType;
__off[0] = -1;
if (__length > 1)
__off[1] = 0;
_DifferenceType __k = 0;
for (_DifferenceType __j = 2; __j <= __length; __j++)
{
while ((__k >= 0) && !(__elements[__k] == __elements[__j-1]))
__k = __off[__k];
__off[__j] = ++__k;
}
}
// Generic parallel find algorithm (requires random access iterator).
/** @brief Parallel std::search.
* @param __begin1 Begin iterator of first sequence.
* @param __end1 End iterator of first sequence.
* @param __begin2 Begin iterator of second sequence.
* @param __end2 End iterator of second sequence.
* @param __pred Find predicate.
* @return Place of finding in first sequences. */
template<typename __RAIter1,
typename __RAIter2,
typename _Pred>
__RAIter1
__search_template(__RAIter1 __begin1, __RAIter1 __end1,
__RAIter2 __begin2, __RAIter2 __end2,
_Pred __pred)
{
typedef std::iterator_traits<__RAIter1> _TraitsType;
typedef typename _TraitsType::difference_type _DifferenceType;
_GLIBCXX_CALL((__end1 - __begin1) + (__end2 - __begin2));
_DifferenceType __pattern_length = __end2 - __begin2;
// Pattern too short.
if(__pattern_length <= 0)
return __end1;
// Last point to start search.
_DifferenceType __input_length = (__end1 - __begin1) - __pattern_length;
// Where is first occurrence of pattern? defaults to end.
_DifferenceType __result = (__end1 - __begin1);
_DifferenceType *__splitters;
// Pattern too long.
if (__input_length < 0)
return __end1;
omp_lock_t __result_lock;
omp_init_lock(&__result_lock);
_ThreadIndex __num_threads = std::max<_DifferenceType>
(1, std::min<_DifferenceType>(__input_length,
__get_max_threads()));
_DifferenceType __advances[__pattern_length];
__calc_borders(__begin2, __pattern_length, __advances);
# pragma omp parallel num_threads(__num_threads)
{
# pragma omp single
{
__num_threads = omp_get_num_threads();
__splitters = new _DifferenceType[__num_threads + 1];
__equally_split(__input_length, __num_threads, __splitters);
}
_ThreadIndex __iam = omp_get_thread_num();
_DifferenceType __start = __splitters[__iam],
__stop = __splitters[__iam + 1];
_DifferenceType __pos_in_pattern = 0;
bool __found_pattern = false;
while (__start <= __stop && !__found_pattern)
{
// Get new value of result.
#pragma omp flush(__result)
// No chance for this thread to find first occurrence.
if (__result < __start)
break;
while (__pred(__begin1[__start + __pos_in_pattern],
__begin2[__pos_in_pattern]))
{
++__pos_in_pattern;
if (__pos_in_pattern == __pattern_length)
{
// Found new candidate for result.
omp_set_lock(&__result_lock);
__result = std::min(__result, __start);
omp_unset_lock(&__result_lock);
__found_pattern = true;
break;
}
}
// Make safe jump.
__start += (__pos_in_pattern - __advances[__pos_in_pattern]);
__pos_in_pattern = (__advances[__pos_in_pattern] < 0
? 0 : __advances[__pos_in_pattern]);
}
} //parallel
omp_destroy_lock(&__result_lock);
delete[] __splitters;
// Return iterator on found element.
return (__begin1 + __result);
}
} // end namespace
#endif /* _GLIBCXX_PARALLEL_SEARCH_H */