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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/partition.h
+ * @brief Parallel implementation of std::partition(),
+ * std::nth_element(), and std::partial_sort().
+ * This file is a GNU parallel extension to the Standard C++ Library.
+ */
+
+// Written by Johannes Singler and Felix Putze.
+
+#ifndef _GLIBCXX_PARALLEL_PARTITION_H
+#define _GLIBCXX_PARALLEL_PARTITION_H 1
+
+#include
+#include
+#include
+#include
+#include
+
+/** @brief Decide whether to declare certain variables volatile. */
+#define _GLIBCXX_VOLATILE volatile
+
+namespace __gnu_parallel
+{
+/** @brief Parallel implementation of std::partition.
+ * @param begin Begin iterator of input sequence to split.
+ * @param end End iterator of input sequence to split.
+ * @param pred Partition predicate, possibly including some kind of pivot.
+ * @param num_threads Maximum number of threads to use for this task.
+ * @return Number of elements not fulfilling the predicate. */
+template
+ typename std::iterator_traits::difference_type
+ parallel_partition(RandomAccessIterator begin, RandomAccessIterator end,
+ Predicate pred, thread_index_t num_threads)
+ {
+ typedef std::iterator_traits traits_type;
+ typedef typename traits_type::value_type value_type;
+ typedef typename traits_type::difference_type difference_type;
+
+ difference_type n = end - begin;
+
+ _GLIBCXX_CALL(n)
+
+ const _Settings& __s = _Settings::get();
+
+ // Shared.
+ _GLIBCXX_VOLATILE difference_type left = 0, right = n - 1;
+ _GLIBCXX_VOLATILE difference_type leftover_left, leftover_right;
+ _GLIBCXX_VOLATILE difference_type leftnew, rightnew;
+
+ bool* reserved_left = NULL, * reserved_right = NULL;
+
+ difference_type chunk_size = __s.partition_chunk_size;
+
+ omp_lock_t result_lock;
+ omp_init_lock(&result_lock);
+
+ //at least two chunks per thread
+ if(right - left + 1 >= 2 * num_threads * chunk_size)
+# pragma omp parallel num_threads(num_threads)
+ {
+# pragma omp single
+ {
+ num_threads = omp_get_num_threads();
+ reserved_left = new bool[num_threads];
+ reserved_right = new bool[num_threads];
+
+ if (__s.partition_chunk_share > 0.0)
+ chunk_size = std::max(__s.partition_chunk_size,
+ (double)n * __s.partition_chunk_share
+ / (double)num_threads);
+ else
+ chunk_size = __s.partition_chunk_size;
+ }
+
+ while (right - left + 1 >= 2 * num_threads * chunk_size)
+ {
+# pragma omp single
+ {
+ difference_type num_chunks = (right - left + 1) / chunk_size;
+
+ for (int r = 0; r < num_threads; ++r)
+ {
+ reserved_left[r] = false;
+ reserved_right[r] = false;
+ }
+ leftover_left = 0;
+ leftover_right = 0;
+ } //implicit barrier
+
+ // Private.
+ difference_type thread_left, thread_left_border,
+ thread_right, thread_right_border;
+ thread_left = left + 1;
+
+ // Just to satisfy the condition below.
+ thread_left_border = thread_left - 1;
+ thread_right = n - 1;
+ thread_right_border = thread_right + 1;
+
+ bool iam_finished = false;
+ while (!iam_finished)
+ {
+ if (thread_left > thread_left_border)
+ {
+ omp_set_lock(&result_lock);
+ if (left + (chunk_size - 1) > right)
+ iam_finished = true;
+ else
+ {
+ thread_left = left;
+ thread_left_border = left + (chunk_size - 1);
+ left += chunk_size;
+ }
+ omp_unset_lock(&result_lock);
+ }
+
+ if (thread_right < thread_right_border)
+ {
+ omp_set_lock(&result_lock);
+ if (left > right - (chunk_size - 1))
+ iam_finished = true;
+ else
+ {
+ thread_right = right;
+ thread_right_border = right - (chunk_size - 1);
+ right -= chunk_size;
+ }
+ omp_unset_lock(&result_lock);
+ }
+
+ if (iam_finished)
+ break;
+
+ // Swap as usual.
+ while (thread_left < thread_right)
+ {
+ while (pred(begin[thread_left])
+ && thread_left <= thread_left_border)
+ ++thread_left;
+ while (!pred(begin[thread_right])
+ && thread_right >= thread_right_border)
+ --thread_right;
+
+ if (thread_left > thread_left_border
+ || thread_right < thread_right_border)
+ // Fetch new chunk(s).
+ break;
+
+ std::swap(begin[thread_left], begin[thread_right]);
+ ++thread_left;
+ --thread_right;
+ }
+ }
+
+ // Now swap the leftover chunks to the right places.
+ if (thread_left <= thread_left_border)
+# pragma omp atomic
+ ++leftover_left;
+ if (thread_right >= thread_right_border)
+# pragma omp atomic
+ ++leftover_right;
+
+# pragma omp barrier
+
+# pragma omp single
+ {
+ leftnew = left - leftover_left * chunk_size;
+ rightnew = right + leftover_right * chunk_size;
+ }
+
+# pragma omp barrier
+
+ // <=> thread_left_border + (chunk_size - 1) >= leftnew
+ if (thread_left <= thread_left_border
+ && thread_left_border >= leftnew)
+ {
+ // Chunk already in place, reserve spot.
+ reserved_left[(left - (thread_left_border + 1)) / chunk_size]
+ = true;
+ }
+
+ // <=> thread_right_border - (chunk_size - 1) <= rightnew
+ if (thread_right >= thread_right_border
+ && thread_right_border <= rightnew)
+ {
+ // Chunk already in place, reserve spot.
+ reserved_right[((thread_right_border - 1) - right)
+ / chunk_size] = true;
+ }
+
+# pragma omp barrier
+
+ if (thread_left <= thread_left_border
+ && thread_left_border < leftnew)
+ {
+ // Find spot and swap.
+ difference_type swapstart = -1;
+ omp_set_lock(&result_lock);
+ for (int r = 0; r < leftover_left; ++r)
+ if (!reserved_left[r])
+ {
+ reserved_left[r] = true;
+ swapstart = left - (r + 1) * chunk_size;
+ break;
+ }
+ omp_unset_lock(&result_lock);
+
+#if _GLIBCXX_ASSERTIONS
+ _GLIBCXX_PARALLEL_ASSERT(swapstart != -1);
+#endif
+
+ std::swap_ranges(begin + thread_left_border
+ - (chunk_size - 1),
+ begin + thread_left_border + 1,
+ begin + swapstart);
+ }
+
+ if (thread_right >= thread_right_border
+ && thread_right_border > rightnew)
+ {
+ // Find spot and swap
+ difference_type swapstart = -1;
+ omp_set_lock(&result_lock);
+ for (int r = 0; r < leftover_right; ++r)
+ if (!reserved_right[r])
+ {
+ reserved_right[r] = true;
+ swapstart = right + r * chunk_size + 1;
+ break;
+ }
+ omp_unset_lock(&result_lock);
+
+#if _GLIBCXX_ASSERTIONS
+ _GLIBCXX_PARALLEL_ASSERT(swapstart != -1);
+#endif
+
+ std::swap_ranges(begin + thread_right_border,
+ begin + thread_right_border + chunk_size,
+ begin + swapstart);
+ }
+#if _GLIBCXX_ASSERTIONS
+# pragma omp barrier
+
+# pragma omp single
+ {
+ for (int r = 0; r < leftover_left; ++r)
+ _GLIBCXX_PARALLEL_ASSERT(reserved_left[r]);
+ for (int r = 0; r < leftover_right; ++r)
+ _GLIBCXX_PARALLEL_ASSERT(reserved_right[r]);
+ }
+
+# pragma omp barrier
+#endif
+
+# pragma omp barrier
+
+ left = leftnew;
+ right = rightnew;
+ }
+# pragma omp flush(left, right)
+ } // end "recursion" //parallel
+
+ difference_type final_left = left, final_right = right;
+
+ while (final_left < final_right)
+ {
+ // Go right until key is geq than pivot.
+ while (pred(begin[final_left]) && final_left < final_right)
+ ++final_left;
+
+ // Go left until key is less than pivot.
+ while (!pred(begin[final_right]) && final_left < final_right)
+ --final_right;
+
+ if (final_left == final_right)
+ break;
+ std::swap(begin[final_left], begin[final_right]);
+ ++final_left;
+ --final_right;
+ }
+
+ // All elements on the left side are < piv, all elements on the
+ // right are >= piv
+ delete[] reserved_left;
+ delete[] reserved_right;
+
+ omp_destroy_lock(&result_lock);
+
+ // Element "between" final_left and final_right might not have
+ // been regarded yet
+ if (final_left < n && !pred(begin[final_left]))
+ // Really swapped.
+ return final_left;
+ else
+ return final_left + 1;
+ }
+
+/**
+ * @brief Parallel implementation of std::nth_element().
+ * @param begin Begin iterator of input sequence.
+ * @param nth Iterator of element that must be in position afterwards.
+ * @param end End iterator of input sequence.
+ * @param comp Comparator.
+ */
+template
+ void
+ parallel_nth_element(RandomAccessIterator begin, RandomAccessIterator nth,
+ RandomAccessIterator end, Comparator comp)
+ {
+ typedef std::iterator_traits traits_type;
+ typedef typename traits_type::value_type value_type;
+ typedef typename traits_type::difference_type difference_type;
+
+ _GLIBCXX_CALL(end - begin)
+
+ RandomAccessIterator split;
+ random_number rng;
+
+ const _Settings& __s = _Settings::get();
+ difference_type minimum_length = std::max(2,
+ std::max(__s.nth_element_minimal_n, __s.partition_minimal_n));
+
+ // Break if input range to small.
+ while (static_cast(end - begin) >= minimum_length)
+ {
+ difference_type n = end - begin;
+
+ RandomAccessIterator pivot_pos = begin + rng(n);
+
+ // Swap pivot_pos value to end.
+ if (pivot_pos != (end - 1))
+ std::swap(*pivot_pos, *(end - 1));
+ pivot_pos = end - 1;
+
+ // XXX Comparator must have first_value_type, second_value_type,
+ // result_type
+ // Comparator == __gnu_parallel::lexicographic >
+ // pivot_pos == std::pair*
+ // XXX binder2nd only for RandomAccessIterators??
+ __gnu_parallel::binder2nd
+ pred(comp, *pivot_pos);
+
+ // Divide, leave pivot unchanged in last place.
+ RandomAccessIterator split_pos1, split_pos2;
+ split_pos1 = begin + parallel_partition(begin, end - 1, pred,
+ get_max_threads());
+
+ // Left side: < pivot_pos; right side: >= pivot_pos
+
+ // Swap pivot back to middle.
+ if (split_pos1 != pivot_pos)
+ std::swap(*split_pos1, *pivot_pos);
+ pivot_pos = split_pos1;
+
+ // In case all elements are equal, split_pos1 == 0
+ if ((split_pos1 + 1 - begin) < (n >> 7)
+ || (end - split_pos1) < (n >> 7))
+ {
+ // Very unequal split, one part smaller than one 128th
+ // elements not strictly larger than the pivot.
+ __gnu_parallel::unary_negate<__gnu_parallel::
+ binder1st, value_type>
+ pred(__gnu_parallel::binder1st(comp, *pivot_pos));
+
+ // Find other end of pivot-equal range.
+ split_pos2 = __gnu_sequential::partition(split_pos1 + 1,
+ end, pred);
+ }
+ else
+ // Only skip the pivot.
+ split_pos2 = split_pos1 + 1;
+
+ // Compare iterators.
+ if (split_pos2 <= nth)
+ begin = split_pos2;
+ else if (nth < split_pos1)
+ end = split_pos1;
+ else
+ break;
+ }
+
+ // Only at most _Settings::partition_minimal_n elements left.
+ __gnu_sequential::nth_element(begin, nth, end, comp);
+ }
+
+/** @brief Parallel implementation of std::partial_sort().
+* @param begin Begin iterator of input sequence.
+* @param middle Sort until this position.
+* @param end End iterator of input sequence.
+* @param comp Comparator. */
+template
+ void
+ parallel_partial_sort(RandomAccessIterator begin,
+ RandomAccessIterator middle,
+ RandomAccessIterator end, Comparator comp)
+ {
+ parallel_nth_element(begin, middle, end, comp);
+ std::sort(begin, middle, comp);
+ }
+
+} //namespace __gnu_parallel
+
+#undef _GLIBCXX_VOLATILE
+
+#endif /* _GLIBCXX_PARALLEL_PARTITION_H */