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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
+// <http://www.gnu.org/licenses/>.
+
+/** @file parallel/random_number.h
+ * @brief Random number generator based on the Mersenne twister.
+ * This file is a GNU parallel extension to the Standard C++ Library.
+ */
+
+// Written by Johannes Singler.
+
+#ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
+#define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
+
+#include <parallel/types.h>
+#include <tr1/random>
+
+namespace __gnu_parallel
+{
+ /** @brief Random number generator, based on the Mersenne twister. */
+ class random_number
+ {
+ private:
+ std::tr1::mt19937 mt;
+ uint64 supremum;
+ uint64 RAND_SUP;
+ double supremum_reciprocal;
+ double RAND_SUP_REC;
+
+ // Assumed to be twice as long as the usual random number.
+ uint64 cache;
+
+ // Bit results.
+ int bits_left;
+
+ static uint32
+ scale_down(uint64 x,
+#if _GLIBCXX_SCALE_DOWN_FPU
+ uint64 /*supremum*/, double supremum_reciprocal)
+#else
+ uint64 supremum, double /*supremum_reciprocal*/)
+#endif
+ {
+#if _GLIBCXX_SCALE_DOWN_FPU
+ return uint32(x * supremum_reciprocal);
+#else
+ return static_cast<uint32>(x % supremum);
+#endif
+ }
+
+ public:
+ /** @brief Default constructor. Seed with 0. */
+ random_number()
+ : mt(0), supremum(0x100000000ULL),
+ RAND_SUP(1ULL << (sizeof(uint32) * 8)),
+ supremum_reciprocal(double(supremum) / double(RAND_SUP)),
+ RAND_SUP_REC(1.0 / double(RAND_SUP)),
+ cache(0), bits_left(0) { }
+
+ /** @brief Constructor.
+ * @param seed Random seed.
+ * @param supremum Generate integer random numbers in the
+ * interval @c [0,supremum). */
+ random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
+ : mt(seed), supremum(supremum),
+ RAND_SUP(1ULL << (sizeof(uint32) * 8)),
+ supremum_reciprocal(double(supremum) / double(RAND_SUP)),
+ RAND_SUP_REC(1.0 / double(RAND_SUP)),
+ cache(0), bits_left(0) { }
+
+ /** @brief Generate unsigned random 32-bit integer. */
+ uint32
+ operator()()
+ { return scale_down(mt(), supremum, supremum_reciprocal); }
+
+ /** @brief Generate unsigned random 32-bit integer in the
+ interval @c [0,local_supremum). */
+ uint32
+ operator()(uint64 local_supremum)
+ {
+ return scale_down(mt(), local_supremum,
+ double(local_supremum * RAND_SUP_REC));
+ }
+
+ /** @brief Generate a number of random bits, run-time parameter.
+ * @param bits Number of bits to generate. */
+ unsigned long
+ genrand_bits(int bits)
+ {
+ unsigned long res = cache & ((1 << bits) - 1);
+ cache = cache >> bits;
+ bits_left -= bits;
+ if (bits_left < 32)
+ {
+ cache |= ((uint64(mt())) << bits_left);
+ bits_left += 32;
+ }
+ return res;
+ }
+};
+
+} // namespace __gnu_parallel
+
+#endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */