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// -*- C++ -*-
// Copyright (C) 2007, 2008, 2009 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 advances Returned offsets.
*/
template<typename RandomAccessIterator, typename _DifferenceTp>
void
calc_borders(RandomAccessIterator elements, _DifferenceTp length,
_DifferenceTp* off)
{
typedef _DifferenceTp difference_type;
off[0] = -1;
if (length > 1)
off[1] = 0;
difference_type k = 0;
for (difference_type 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 _RandomAccessIterator1,
typename _RandomAccessIterator2,
typename Pred>
_RandomAccessIterator1
search_template(_RandomAccessIterator1 begin1, _RandomAccessIterator1 end1,
_RandomAccessIterator2 begin2, _RandomAccessIterator2 end2,
Pred pred)
{
typedef std::iterator_traits<_RandomAccessIterator1> traits_type;
typedef typename traits_type::difference_type difference_type;
_GLIBCXX_CALL((end1 - begin1) + (end2 - begin2));
difference_type pattern_length = end2 - begin2;
// Pattern too short.
if(pattern_length <= 0)
return end1;
// Last point to start search.
difference_type input_length = (end1 - begin1) - pattern_length;
// Where is first occurrence of pattern? defaults to end.
difference_type result = (end1 - begin1);
difference_type *splitters;
// Pattern too long.
if (input_length < 0)
return end1;
omp_lock_t result_lock;
omp_init_lock(&result_lock);
thread_index_t num_threads =
std::max<difference_type>(1,
std::min<difference_type>(input_length, get_max_threads()));
difference_type 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 difference_type[num_threads + 1];
equally_split(input_length, num_threads, splitters);
}
thread_index_t iam = omp_get_thread_num();
difference_type start = splitters[iam], stop = splitters[iam + 1];
difference_type 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 */
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