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parallel
merge.h
// -*- C++ -*- // Copyright (C) 2007-2018 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 _RAIter1, typename _RAIter2, typename _OutputIterator, typename _DifferenceTp, typename _Compare> _OutputIterator __merge_advance_usual(_RAIter1& __begin1, _RAIter1 __end1, _RAIter2& __begin2, _RAIter2 __end2, _OutputIterator __target, _DifferenceTp __max_length, _Compare __comp) { typedef _DifferenceTp _DifferenceType; 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 _RAIter1, typename _RAIter2, typename _OutputIterator, typename _DifferenceTp, typename _Compare> _OutputIterator __merge_advance_movc(_RAIter1& __begin1, _RAIter1 __end1, _RAIter2& __begin2, _RAIter2 __end2, _OutputIterator __target, _DifferenceTp __max_length, _Compare __comp) { typedef _DifferenceTp _DifferenceType; typedef typename std::iterator_traits<_RAIter1>::value_type _ValueType1; typedef typename std::iterator_traits<_RAIter2>::value_type _ValueType2; #if _GLIBCXX_PARALLEL_ASSERTIONS _GLIBCXX_PARALLEL_ASSERT(__max_length >= 0); #endif while (__begin1 != __end1 && __begin2 != __end2 && __max_length > 0) { _RAIter1 __next1 = __begin1 + 1; _RAIter2 __next2 = __begin2 + 1; _ValueType1 __element1 = *__begin1; _ValueType2 __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 _RAIter1, typename _RAIter2, typename _OutputIterator, typename _DifferenceTp, typename _Compare> inline _OutputIterator __merge_advance(_RAIter1& __begin1, _RAIter1 __end1, _RAIter2& __begin2, _RAIter2 __end2, _OutputIterator __target, _DifferenceTp __max_length, _Compare __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 _RAIter1, typename _RAIter2, typename _RAIter3, typename _Compare> inline _RAIter3 __parallel_merge_advance(_RAIter1& __begin1, _RAIter1 __end1, _RAIter2& __begin2, // different iterators, parallel implementation // not available _RAIter2 __end2, _RAIter3 __target, typename std::iterator_traits<_RAIter1>:: difference_type __max_length, _Compare __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 _RAIter1, typename _RAIter3, typename _Compare> inline _RAIter3 __parallel_merge_advance(_RAIter1& __begin1, _RAIter1 __end1, _RAIter1& __begin2, _RAIter1 __end2, _RAIter3 __target, typename std::iterator_traits<_RAIter1>:: difference_type __max_length, _Compare __comp) { typedef typename std::iterator_traits<_RAIter1>::value_type _ValueType; typedef typename std::iterator_traits<_RAIter1>:: difference_type _DifferenceType1 /* == difference_type2 */; typedef typename std::iterator_traits<_RAIter3>:: difference_type _DifferenceType3; typedef typename std::pair<_RAIter1, _RAIter1> _IteratorPair; _IteratorPair __seqs[2] = { std::make_pair(__begin1, __end1), std::make_pair(__begin2, __end2) }; _RAIter3 __target_end = parallel_multiway_merge < /* __stable = */ true, /* __sentinels = */ false> (__seqs, __seqs + 2, __target, multiway_merge_exact_splitting < /* __stable = */ true, _IteratorPair*, _Compare, _DifferenceType1>, __max_length, __comp, omp_get_max_threads()); return __target_end; } } //namespace __gnu_parallel #endif /* _GLIBCXX_PARALLEL_MERGE_H */
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