252 lines
9.4 KiB
C++
252 lines
9.4 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2020 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 _RAIter1, typename _RAIter2,
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typename _OutputIterator, typename _DifferenceTp,
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typename _Compare>
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_OutputIterator
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__merge_advance_usual(_RAIter1& __begin1, _RAIter1 __end1,
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_RAIter2& __begin2, _RAIter2 __end2,
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_OutputIterator __target,
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_DifferenceTp __max_length, _Compare __comp)
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{
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typedef _DifferenceTp _DifferenceType;
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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 _RAIter1, typename _RAIter2,
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typename _OutputIterator, typename _DifferenceTp,
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typename _Compare>
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_OutputIterator
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__merge_advance_movc(_RAIter1& __begin1, _RAIter1 __end1,
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_RAIter2& __begin2, _RAIter2 __end2,
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_OutputIterator __target,
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_DifferenceTp __max_length, _Compare __comp)
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{
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typedef _DifferenceTp _DifferenceType;
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typedef typename std::iterator_traits<_RAIter1>::value_type
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_ValueType1;
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typedef typename std::iterator_traits<_RAIter2>::value_type
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_ValueType2;
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#if _GLIBCXX_PARALLEL_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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_RAIter1 __next1 = __begin1 + 1;
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_RAIter2 __next2 = __begin2 + 1;
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_ValueType1 __element1 = *__begin1;
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_ValueType2 __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 _RAIter1, typename _RAIter2,
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typename _OutputIterator, typename _DifferenceTp,
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typename _Compare>
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inline _OutputIterator
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__merge_advance(_RAIter1& __begin1, _RAIter1 __end1,
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_RAIter2& __begin2, _RAIter2 __end2,
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_OutputIterator __target, _DifferenceTp __max_length,
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_Compare __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,
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__target, __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 _RAIter1, typename _RAIter2,
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typename _RAIter3, typename _Compare>
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inline _RAIter3
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__parallel_merge_advance(_RAIter1& __begin1, _RAIter1 __end1,
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_RAIter2& __begin2,
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// different iterators, parallel implementation
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// not available
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_RAIter2 __end2, _RAIter3 __target, typename
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std::iterator_traits<_RAIter1>::
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difference_type __max_length, _Compare __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 _RAIter1, typename _RAIter3,
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typename _Compare>
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inline _RAIter3
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__parallel_merge_advance(_RAIter1& __begin1, _RAIter1 __end1,
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_RAIter1& __begin2, _RAIter1 __end2,
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_RAIter3 __target, typename
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std::iterator_traits<_RAIter1>::
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difference_type __max_length, _Compare __comp)
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{
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typedef typename
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std::iterator_traits<_RAIter1>::value_type _ValueType;
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typedef typename std::iterator_traits<_RAIter1>::
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difference_type _DifferenceType1 /* == difference_type2 */;
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typedef typename std::iterator_traits<_RAIter3>::
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difference_type _DifferenceType3;
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typedef typename std::pair<_RAIter1, _RAIter1>
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_IteratorPair;
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_IteratorPair __seqs[2] = { std::make_pair(__begin1, __end1),
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std::make_pair(__begin2, __end2) };
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_RAIter3 __target_end = parallel_multiway_merge
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< /* __stable = */ true, /* __sentinels = */ false>
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(__seqs, __seqs + 2, __target, multiway_merge_exact_splitting
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< /* __stable = */ true, _IteratorPair*,
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_Compare, _DifferenceType1>, __max_length, __comp,
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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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