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+// -*- C++ -*-
+
+// Copyright (C) 2007, 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
+// <http://www.gnu.org/licenses/>.
+
+/** @file parallel/equally_split.h
+ * This file is a GNU parallel extension to the Standard C++ Library.
+ */
+
+// Written by Johannes Singler.
+
+#ifndef _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H
+#define _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H 1
+
+namespace __gnu_parallel
+{
+/** @brief Function to split a sequence into parts of almost equal size.
+ *
+ * The resulting sequence s of length num_threads+1 contains the splitting
+ * positions when splitting the range [0,n) into parts of almost
+ * equal size (plus minus 1). The first entry is 0, the last one
+ * n. There may result empty parts.
+ * @param n Number of elements
+ * @param num_threads Number of parts
+ * @param s Splitters
+ * @returns End of splitter sequence, i. e. @c s+num_threads+1 */
+template<typename difference_type, typename OutputIterator>
+ OutputIterator
+ equally_split(difference_type n, thread_index_t num_threads, OutputIterator s)
+ {
+ difference_type chunk_length = n / num_threads;
+ difference_type num_longer_chunks = n % num_threads;
+ difference_type pos = 0;
+ for (thread_index_t i = 0; i < num_threads; ++i)
+ {
+ *s++ = pos;
+ pos += (i < num_longer_chunks) ? (chunk_length + 1) : chunk_length;
+ }
+ *s++ = n;
+ return s;
+ }
+
+
+/** @brief Function to split a sequence into parts of almost equal size.
+ *
+ * Returns the position of the splitting point between
+ * thread number thread_no (included) and
+ * thread number thread_no+1 (excluded).
+ * @param n Number of elements
+ * @param num_threads Number of parts
+ * @returns _SplittingAlgorithm point */
+template<typename difference_type>
+ difference_type
+ equally_split_point(difference_type n,
+ thread_index_t num_threads,
+ thread_index_t thread_no)
+ {
+ difference_type chunk_length = n / num_threads;
+ difference_type num_longer_chunks = n % num_threads;
+ if (thread_no < num_longer_chunks)
+ return thread_no * (chunk_length + 1);
+ else
+ return num_longer_chunks * (chunk_length + 1)
+ + (thread_no - num_longer_chunks) * chunk_length;
+ }
+}
+
+#endif /* _GLIBCXX_PARALLEL_EQUALLY_SPLIT_H */