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+// -*- 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
+// .
+
+/** @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
+#include
+
+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
+ 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
+ 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::value_type
+ value_type1;
+ typedef typename std::iterator_traits::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
+ 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
+ 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::
+ 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
+ inline RandomAccessIterator3
+ parallel_merge_advance(RandomAccessIterator1& begin1,
+ RandomAccessIterator1 end1,
+ RandomAccessIterator1& begin2,
+ RandomAccessIterator1 end2,
+ RandomAccessIterator3 target, typename
+ std::iterator_traits::
+ difference_type max_length, Comparator comp)
+ {
+ typedef typename
+ std::iterator_traits::value_type value_type;
+ typedef typename std::iterator_traits::
+ difference_type difference_type1 /* == difference_type2 */;
+ typedef typename std::iterator_traits::
+ difference_type difference_type3;
+ typedef typename std::pair
+ 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 */