125 lines
3.7 KiB
C++
125 lines
3.7 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007, 2008, 2009 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the terms
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// of the GNU General Public License as published by the Free Software
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// Foundation; either version 3, or (at your option) any later
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// version.
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// This library is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file parallel/random_number.h
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* @brief Random number generator based on the Mersenne twister.
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* This file is a GNU parallel extension to the Standard C++ Library.
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*/
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// Written by Johannes Singler.
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#ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
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#define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
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#include <parallel/types.h>
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#include <tr1/random>
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namespace __gnu_parallel
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{
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/** @brief Random number generator, based on the Mersenne twister. */
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class random_number
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{
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private:
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std::tr1::mt19937 mt;
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uint64 supremum;
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uint64 RAND_SUP;
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double supremum_reciprocal;
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double RAND_SUP_REC;
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// Assumed to be twice as long as the usual random number.
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uint64 cache;
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// Bit results.
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int bits_left;
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static uint32
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scale_down(uint64 x,
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#if _GLIBCXX_SCALE_DOWN_FPU
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uint64 /*supremum*/, double supremum_reciprocal)
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#else
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uint64 supremum, double /*supremum_reciprocal*/)
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#endif
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{
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#if _GLIBCXX_SCALE_DOWN_FPU
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return uint32(x * supremum_reciprocal);
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#else
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return static_cast<uint32>(x % supremum);
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#endif
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}
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public:
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/** @brief Default constructor. Seed with 0. */
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random_number()
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: mt(0), supremum(0x100000000ULL),
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RAND_SUP(1ULL << (sizeof(uint32) * 8)),
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supremum_reciprocal(double(supremum) / double(RAND_SUP)),
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RAND_SUP_REC(1.0 / double(RAND_SUP)),
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cache(0), bits_left(0) { }
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/** @brief Constructor.
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* @param seed Random seed.
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* @param supremum Generate integer random numbers in the
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* interval @c [0,supremum). */
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random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
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: mt(seed), supremum(supremum),
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RAND_SUP(1ULL << (sizeof(uint32) * 8)),
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supremum_reciprocal(double(supremum) / double(RAND_SUP)),
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RAND_SUP_REC(1.0 / double(RAND_SUP)),
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cache(0), bits_left(0) { }
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/** @brief Generate unsigned random 32-bit integer. */
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uint32
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operator()()
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{ return scale_down(mt(), supremum, supremum_reciprocal); }
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/** @brief Generate unsigned random 32-bit integer in the
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interval @c [0,local_supremum). */
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uint32
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operator()(uint64 local_supremum)
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{
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return scale_down(mt(), local_supremum,
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double(local_supremum * RAND_SUP_REC));
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}
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/** @brief Generate a number of random bits, run-time parameter.
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* @param bits Number of bits to generate. */
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unsigned long
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genrand_bits(int bits)
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{
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unsigned long res = cache & ((1 << bits) - 1);
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cache = cache >> bits;
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bits_left -= bits;
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if (bits_left < 32)
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{
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cache |= ((uint64(mt())) << bits_left);
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bits_left += 32;
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}
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return res;
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}
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};
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} // namespace __gnu_parallel
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#endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */
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