// -*- 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/merge.h
* @brief Parallel implementation of std::merge().
* This file is a GNU parallel extension to the Standard C++ Library.
*/
// Written by Johannes Singler.
#ifndef _GLIBCXX_PARALLEL_MERGE_H
#define _GLIBCXX_PARALLEL_MERGE_H 1
#include <parallel/basic_iterator.h>
#include <bits/stl_algo.h>
namespace __gnu_parallel
{
/** @brief Merge routine being able to merge only the @c max_length
* smallest elements.
*
* The @c begin iterators are advanced accordingly, they might not
* reach @c end, in contrast to the usual variant.
* @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 target Target begin iterator.
* @param max_length Maximum number of elements to merge.
* @param comp Comparator.
* @return Output end iterator. */
template<typename RandomAccessIterator1, typename RandomAccessIterator2,
typename OutputIterator, typename _DifferenceTp,
typename Comparator>
OutputIterator
merge_advance_usual(RandomAccessIterator1& begin1,
RandomAccessIterator1 end1,
RandomAccessIterator2& begin2,
RandomAccessIterator2 end2, OutputIterator target,
_DifferenceTp max_length, Comparator comp)
{
typedef _DifferenceTp difference_type;
while (begin1 != end1 && begin2 != end2 && max_length > 0)
{
// array1[i1] < array0[i0]
if (comp(*begin2, *begin1))
*target++ = *begin2++;
else
*target++ = *begin1++;
--max_length;
}
if (begin1 != end1)
{
target = std::copy(begin1, begin1 + max_length, target);
begin1 += max_length;
}
else
{
target = std::copy(begin2, begin2 + max_length, target);
begin2 += max_length;
}
return target;
}
/** @brief Merge routine being able to merge only the @c max_length
* smallest elements.
*
* The @c begin iterators are advanced accordingly, they might not
* reach @c end, in contrast to the usual variant.
* Specially designed code should allow the compiler to generate
* conditional moves instead of branches.
* @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 target Target begin iterator.
* @param max_length Maximum number of elements to merge.
* @param comp Comparator.
* @return Output end iterator. */
template<typename RandomAccessIterator1, typename RandomAccessIterator2,
typename OutputIterator, typename _DifferenceTp,
typename Comparator>
OutputIterator
merge_advance_movc(RandomAccessIterator1& begin1,
RandomAccessIterator1 end1,
RandomAccessIterator2& begin2,
RandomAccessIterator2 end2,
OutputIterator target,
_DifferenceTp max_length, Comparator comp)
{
typedef _DifferenceTp difference_type;
typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
value_type1;
typedef typename std::iterator_traits<RandomAccessIterator2>::value_type
value_type2;
#if _GLIBCXX_ASSERTIONS
_GLIBCXX_PARALLEL_ASSERT(max_length >= 0);
#endif
while (begin1 != end1 && begin2 != end2 && max_length > 0)
{
RandomAccessIterator1 next1 = begin1 + 1;
RandomAccessIterator2 next2 = begin2 + 1;
value_type1 element1 = *begin1;
value_type2 element2 = *begin2;
if (comp(element2, element1))
{
element1 = element2;
begin2 = next2;
}
else
begin1 = next1;
*target = element1;
++target;
--max_length;
}
if (begin1 != end1)
{
target = std::copy(begin1, begin1 + max_length, target);
begin1 += max_length;
}
else
{
target = std::copy(begin2, begin2 + max_length, target);
begin2 += max_length;
}
return target;
}
/** @brief Merge routine being able to merge only the @c max_length
* smallest elements.
*
* The @c begin iterators are advanced accordingly, they might not
* reach @c end, in contrast to the usual variant.
* Static switch on whether to use the conditional-move variant.
* @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 target Target begin iterator.
* @param max_length Maximum number of elements to merge.
* @param comp Comparator.
* @return Output end iterator. */
template<typename RandomAccessIterator1, typename RandomAccessIterator2,
typename OutputIterator, typename _DifferenceTp,
typename Comparator>
inline OutputIterator
merge_advance(RandomAccessIterator1& begin1, RandomAccessIterator1 end1,
RandomAccessIterator2& begin2, RandomAccessIterator2 end2,
OutputIterator target, _DifferenceTp max_length,
Comparator comp)
{
_GLIBCXX_CALL(max_length)
return merge_advance_movc(begin1, end1, begin2, end2, target,
max_length, comp);
}
/** @brief Merge routine fallback to sequential in case the
iterators of the two input sequences are of different type.
* @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 target Target begin iterator.
* @param max_length Maximum number of elements to merge.
* @param comp Comparator.
* @return Output end iterator. */
template<typename RandomAccessIterator1, typename RandomAccessIterator2,
typename RandomAccessIterator3, typename Comparator>
inline RandomAccessIterator3
parallel_merge_advance(RandomAccessIterator1& begin1,
RandomAccessIterator1 end1,
RandomAccessIterator2& begin2,
// different iterators, parallel implementation
// not available
RandomAccessIterator2 end2,
RandomAccessIterator3 target, typename
std::iterator_traits<RandomAccessIterator1>::
difference_type max_length, Comparator comp)
{ return merge_advance(begin1, end1, begin2, end2, target,
max_length, comp); }
/** @brief Parallel merge routine being able to merge only the @c
* max_length smallest elements.
*
* The @c begin iterators are advanced accordingly, they might not
* reach @c end, in contrast to the usual variant.
* The functionality is projected onto parallel_multiway_merge.
* @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 target Target begin iterator.
* @param max_length Maximum number of elements to merge.
* @param comp Comparator.
* @return Output end iterator.
*/
template<typename RandomAccessIterator1, typename RandomAccessIterator3,
typename Comparator>
inline RandomAccessIterator3
parallel_merge_advance(RandomAccessIterator1& begin1,
RandomAccessIterator1 end1,
RandomAccessIterator1& begin2,
RandomAccessIterator1 end2,
RandomAccessIterator3 target, typename
std::iterator_traits<RandomAccessIterator1>::
difference_type max_length, Comparator comp)
{
typedef typename
std::iterator_traits<RandomAccessIterator1>::value_type value_type;
typedef typename std::iterator_traits<RandomAccessIterator1>::
difference_type difference_type1 /* == difference_type2 */;
typedef typename std::iterator_traits<RandomAccessIterator3>::
difference_type difference_type3;
typedef typename std::pair<RandomAccessIterator1, RandomAccessIterator1>
iterator_pair;
iterator_pair
seqs[2] = { std::make_pair(begin1, end1),
std::make_pair(begin2, end2) };
RandomAccessIterator3
target_end = parallel_multiway_merge
< /* stable = */ true, /* sentinels = */ false>(
seqs, seqs + 2, target,
multiway_merge_exact_splitting
< /* stable = */ true, iterator_pair*,
Comparator, difference_type1>,
max_length, comp, omp_get_max_threads());
return target_end;
}
} //namespace __gnu_parallel
#endif /* _GLIBCXX_PARALLEL_MERGE_H */