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// -*- C++ -*-
// Copyright (C) 2007-2025 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>
#include <limits>
namespace __gnu_parallel
{
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wlong-long" // LL literal
/** @brief Random number generator, based on the Mersenne twister. */
class _RandomNumber
{
private:
std::tr1::mt19937 _M_mt;
uint64_t _M_supremum;
uint64_t _M_rand_sup;
double _M_supremum_reciprocal;
double _M_rand_sup_reciprocal;
// Assumed to be twice as long as the usual random number.
uint64_t __cache;
// Bit results.
int __bits_left;
static uint32_t
__scale_down(uint64_t __x,
#if _GLIBCXX_SCALE_DOWN_FPU
uint64_t /*_M_supremum*/, double _M_supremum_reciprocal)
#else
uint64_t _M_supremum, double /*_M_supremum_reciprocal*/)
#endif
{
#if _GLIBCXX_SCALE_DOWN_FPU
return uint32_t(__x * _M_supremum_reciprocal);
#else
return static_cast<uint32_t>(__x % _M_supremum);
#endif
}
public:
/** @brief Default constructor. Seed with 0. */
_RandomNumber()
: _M_mt(0), _M_supremum(0x100000000ULL),
_M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
_M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
_M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
__cache(0), __bits_left(0) { }
/** @brief Constructor.
* @param __seed Random __seed.
* @param _M_supremum Generate integer random numbers in the
* interval @c [0,_M_supremum). */
_RandomNumber(uint32_t __seed, uint64_t _M_supremum = 0x100000000ULL)
: _M_mt(__seed), _M_supremum(_M_supremum),
_M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
_M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
_M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
__cache(0), __bits_left(0) { }
/** @brief Generate unsigned random 32-bit integer. */
uint32_t
operator()()
{ return __scale_down(_M_mt(), _M_supremum, _M_supremum_reciprocal); }
/** @brief Generate unsigned random 32-bit integer in the
interval @c [0,local_supremum). */
uint32_t
operator()(uint64_t local_supremum)
{
return __scale_down(_M_mt(), local_supremum,
double(local_supremum * _M_rand_sup_reciprocal));
}
/** @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_t(_M_mt())) << __bits_left);
__bits_left += 32;
}
return __res;
}
};
#pragma GCC diagnostic pop
} // namespace __gnu_parallel
#endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */
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