| // -*- C++ -*- |
| |
| // Copyright (C) 2007-2025 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 */ |
