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126 lines
4.1 KiB
C++
126 lines
4.1 KiB
C++
// -*- C++ -*-
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// Copyright (C) 2007-2020 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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#include <limits>
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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 _RandomNumber
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{
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private:
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std::tr1::mt19937 _M_mt;
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uint64_t _M_supremum;
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uint64_t _M_rand_sup;
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double _M_supremum_reciprocal;
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double _M_rand_sup_reciprocal;
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// Assumed to be twice as long as the usual random number.
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uint64_t __cache;
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// Bit results.
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int __bits_left;
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static uint32_t
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__scale_down(uint64_t __x,
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#if _GLIBCXX_SCALE_DOWN_FPU
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uint64_t /*_M_supremum*/, double _M_supremum_reciprocal)
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#else
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uint64_t _M_supremum, double /*_M_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_t(__x * _M_supremum_reciprocal);
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#else
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return static_cast<uint32_t>(__x % _M_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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_RandomNumber()
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: _M_mt(0), _M_supremum(0x100000000ULL),
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_M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
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_M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
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_M_rand_sup_reciprocal(1.0 / double(_M_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 _M_supremum Generate integer random numbers in the
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* interval @c [0,_M_supremum). */
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_RandomNumber(uint32_t __seed, uint64_t _M_supremum = 0x100000000ULL)
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: _M_mt(__seed), _M_supremum(_M_supremum),
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_M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
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_M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
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_M_rand_sup_reciprocal(1.0 / double(_M_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_t
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operator()()
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{ return __scale_down(_M_mt(), _M_supremum, _M_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_t
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operator()(uint64_t local_supremum)
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{
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return __scale_down(_M_mt(), local_supremum,
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double(local_supremum * _M_rand_sup_reciprocal));
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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_t(_M_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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