262 lines
9.3 KiB
C++
262 lines
9.3 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007, 2008, 2009 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/merge.h
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* @brief Parallel implementation of std::merge().
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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 Johannes Singler.
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#ifndef _GLIBCXX_PARALLEL_MERGE_H
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#define _GLIBCXX_PARALLEL_MERGE_H 1
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#include <parallel/basic_iterator.h>
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#include <bits/stl_algo.h>
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namespace __gnu_parallel
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{
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/** @brief Merge routine being able to merge only the @c max_length
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* smallest elements.
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*
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* The @c begin iterators are advanced accordingly, they might not
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* reach @c end, in contrast to the usual variant.
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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 target Target begin iterator.
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* @param max_length Maximum number of elements to merge.
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* @param comp Comparator.
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* @return Output end iterator. */
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template<typename RandomAccessIterator1, typename RandomAccessIterator2,
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typename OutputIterator, typename _DifferenceTp,
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typename Comparator>
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OutputIterator
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merge_advance_usual(RandomAccessIterator1& begin1,
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RandomAccessIterator1 end1,
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RandomAccessIterator2& begin2,
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RandomAccessIterator2 end2, OutputIterator target,
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_DifferenceTp max_length, Comparator comp)
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{
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typedef _DifferenceTp difference_type;
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while (begin1 != end1 && begin2 != end2 && max_length > 0)
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{
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// array1[i1] < array0[i0]
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if (comp(*begin2, *begin1))
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*target++ = *begin2++;
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else
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*target++ = *begin1++;
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--max_length;
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}
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if (begin1 != end1)
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{
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target = std::copy(begin1, begin1 + max_length, target);
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begin1 += max_length;
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}
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else
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{
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target = std::copy(begin2, begin2 + max_length, target);
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begin2 += max_length;
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}
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return target;
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}
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/** @brief Merge routine being able to merge only the @c max_length
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* smallest elements.
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*
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* The @c begin iterators are advanced accordingly, they might not
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* reach @c end, in contrast to the usual variant.
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* Specially designed code should allow the compiler to generate
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* conditional moves instead of branches.
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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 target Target begin iterator.
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* @param max_length Maximum number of elements to merge.
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* @param comp Comparator.
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* @return Output end iterator. */
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template<typename RandomAccessIterator1, typename RandomAccessIterator2,
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typename OutputIterator, typename _DifferenceTp,
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typename Comparator>
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OutputIterator
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merge_advance_movc(RandomAccessIterator1& begin1,
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RandomAccessIterator1 end1,
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RandomAccessIterator2& begin2,
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RandomAccessIterator2 end2,
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OutputIterator target,
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_DifferenceTp max_length, Comparator comp)
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{
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typedef _DifferenceTp difference_type;
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typedef typename std::iterator_traits<RandomAccessIterator1>::value_type
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value_type1;
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typedef typename std::iterator_traits<RandomAccessIterator2>::value_type
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value_type2;
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#if _GLIBCXX_ASSERTIONS
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_GLIBCXX_PARALLEL_ASSERT(max_length >= 0);
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#endif
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while (begin1 != end1 && begin2 != end2 && max_length > 0)
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{
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RandomAccessIterator1 next1 = begin1 + 1;
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RandomAccessIterator2 next2 = begin2 + 1;
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value_type1 element1 = *begin1;
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value_type2 element2 = *begin2;
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if (comp(element2, element1))
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{
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element1 = element2;
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begin2 = next2;
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}
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else
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begin1 = next1;
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*target = element1;
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++target;
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--max_length;
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}
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if (begin1 != end1)
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{
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target = std::copy(begin1, begin1 + max_length, target);
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begin1 += max_length;
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}
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else
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{
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target = std::copy(begin2, begin2 + max_length, target);
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begin2 += max_length;
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}
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return target;
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}
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/** @brief Merge routine being able to merge only the @c max_length
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* smallest elements.
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*
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* The @c begin iterators are advanced accordingly, they might not
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* reach @c end, in contrast to the usual variant.
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* Static switch on whether to use the conditional-move variant.
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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 target Target begin iterator.
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* @param max_length Maximum number of elements to merge.
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* @param comp Comparator.
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* @return Output end iterator. */
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template<typename RandomAccessIterator1, typename RandomAccessIterator2,
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typename OutputIterator, typename _DifferenceTp,
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typename Comparator>
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inline OutputIterator
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merge_advance(RandomAccessIterator1& begin1, RandomAccessIterator1 end1,
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RandomAccessIterator2& begin2, RandomAccessIterator2 end2,
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OutputIterator target, _DifferenceTp max_length,
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Comparator comp)
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{
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_GLIBCXX_CALL(max_length)
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return merge_advance_movc(begin1, end1, begin2, end2, target,
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max_length, comp);
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}
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/** @brief Merge routine fallback to sequential in case the
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iterators of the two input sequences are of different type.
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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 target Target begin iterator.
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* @param max_length Maximum number of elements to merge.
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* @param comp Comparator.
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* @return Output end iterator. */
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template<typename RandomAccessIterator1, typename RandomAccessIterator2,
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typename RandomAccessIterator3, typename Comparator>
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inline RandomAccessIterator3
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parallel_merge_advance(RandomAccessIterator1& begin1,
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RandomAccessIterator1 end1,
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RandomAccessIterator2& begin2,
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// different iterators, parallel implementation
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// not available
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RandomAccessIterator2 end2,
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RandomAccessIterator3 target, typename
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std::iterator_traits<RandomAccessIterator1>::
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difference_type max_length, Comparator comp)
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{ return merge_advance(begin1, end1, begin2, end2, target,
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max_length, comp); }
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/** @brief Parallel merge routine being able to merge only the @c
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* max_length smallest elements.
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*
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* The @c begin iterators are advanced accordingly, they might not
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* reach @c end, in contrast to the usual variant.
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* The functionality is projected onto parallel_multiway_merge.
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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 target Target begin iterator.
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* @param max_length Maximum number of elements to merge.
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* @param comp Comparator.
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* @return Output end iterator.
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*/
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template<typename RandomAccessIterator1, typename RandomAccessIterator3,
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typename Comparator>
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inline RandomAccessIterator3
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parallel_merge_advance(RandomAccessIterator1& begin1,
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RandomAccessIterator1 end1,
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RandomAccessIterator1& begin2,
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RandomAccessIterator1 end2,
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RandomAccessIterator3 target, typename
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std::iterator_traits<RandomAccessIterator1>::
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difference_type max_length, Comparator comp)
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{
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typedef typename
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std::iterator_traits<RandomAccessIterator1>::value_type value_type;
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typedef typename std::iterator_traits<RandomAccessIterator1>::
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difference_type difference_type1 /* == difference_type2 */;
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typedef typename std::iterator_traits<RandomAccessIterator3>::
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difference_type difference_type3;
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typedef typename std::pair<RandomAccessIterator1, RandomAccessIterator1>
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iterator_pair;
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iterator_pair
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seqs[2] = { std::make_pair(begin1, end1),
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std::make_pair(begin2, end2) };
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RandomAccessIterator3
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target_end = parallel_multiway_merge
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< /* stable = */ true, /* sentinels = */ false>(
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seqs, seqs + 2, target,
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multiway_merge_exact_splitting
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< /* stable = */ true, iterator_pair*,
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Comparator, difference_type1>,
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max_length, comp, omp_get_max_threads());
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return target_end;
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}
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} //namespace __gnu_parallel
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#endif /* _GLIBCXX_PARALLEL_MERGE_H */
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