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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 */
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