1// -*- C++ -*-
2
3// Copyright (C) 2007-2022 Free Software Foundation, Inc.
4//
5// This file is part of the GNU ISO C++ Library.  This library is free
6// software; you can redistribute it and/or modify it under the terms
7// of the GNU General Public License as published by the Free Software
8// Foundation; either version 3, or (at your option) any later
9// version.
10
11// This library is distributed in the hope that it will be useful, but
12// WITHOUT ANY WARRANTY; without even the implied warranty of
13// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
14// General Public License for more details.
15
16// Under Section 7 of GPL version 3, you are granted additional
17// permissions described in the GCC Runtime Library Exception, version
18// 3.1, as published by the Free Software Foundation.
19
20// You should have received a copy of the GNU General Public License and
21// a copy of the GCC Runtime Library Exception along with this program;
22// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
23// <http://www.gnu.org/licenses/>.
24
25/** @file parallel/random_number.h
26 *  @brief Random number generator based on the Mersenne twister.
27 *  This file is a GNU parallel extension to the Standard C++ Library.
28 */
29
30// Written by Johannes Singler.
31
32#ifndef _GLIBCXX_PARALLEL_RANDOM_NUMBER_H
33#define _GLIBCXX_PARALLEL_RANDOM_NUMBER_H 1
34
35#include <parallel/types.h>
36#include <tr1/random>
37#include <limits>
38
39namespace __gnu_parallel
40{
41  /** @brief Random number generator, based on the Mersenne twister. */
42  class _RandomNumber
43  {
44  private:
45    std::tr1::mt19937   _M_mt;
46    uint64_t            _M_supremum;
47    uint64_t            _M_rand_sup;
48    double              _M_supremum_reciprocal;
49    double              _M_rand_sup_reciprocal;
50
51    // Assumed to be twice as long as the usual random number.
52    uint64_t              __cache;
53
54    // Bit results.
55    int __bits_left;
56
57    static uint32_t
58    __scale_down(uint64_t __x,
59#if _GLIBCXX_SCALE_DOWN_FPU
60               uint64_t /*_M_supremum*/, double _M_supremum_reciprocal)
61#else
62               uint64_t _M_supremum, double /*_M_supremum_reciprocal*/)
63#endif
64        {
65#if _GLIBCXX_SCALE_DOWN_FPU
66          return uint32_t(__x * _M_supremum_reciprocal);
67#else
68          return static_cast<uint32_t>(__x % _M_supremum);
69#endif
70        }
71
72  public:
73    /** @brief Default constructor. Seed with 0. */
74    _RandomNumber()
75    : _M_mt(0), _M_supremum(0x100000000ULL),
76      _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
77      _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
78      _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
79      __cache(0), __bits_left(0) { }
80
81    /** @brief Constructor.
82     *  @param __seed Random __seed.
83     *  @param _M_supremum Generate integer random numbers in the
84     *                  interval @c [0,_M_supremum). */
85    _RandomNumber(uint32_t __seed, uint64_t _M_supremum = 0x100000000ULL)
86    : _M_mt(__seed), _M_supremum(_M_supremum),
87      _M_rand_sup(1ULL << std::numeric_limits<uint32_t>::digits),
88      _M_supremum_reciprocal(double(_M_supremum) / double(_M_rand_sup)),
89      _M_rand_sup_reciprocal(1.0 / double(_M_rand_sup)),
90      __cache(0), __bits_left(0) { }
91
92    /** @brief Generate unsigned random 32-bit integer. */
93    uint32_t
94    operator()()
95    { return __scale_down(_M_mt(), _M_supremum, _M_supremum_reciprocal); }
96
97    /** @brief Generate unsigned random 32-bit integer in the
98        interval @c [0,local_supremum). */
99    uint32_t
100    operator()(uint64_t local_supremum)
101    {
102      return __scale_down(_M_mt(), local_supremum,
103                        double(local_supremum * _M_rand_sup_reciprocal));
104    }
105
106    /** @brief Generate a number of random bits, run-time parameter.
107     *  @param __bits Number of bits to generate. */
108    unsigned long
109    __genrand_bits(int __bits)
110    {
111      unsigned long __res = __cache & ((1 << __bits) - 1);
112      __cache = __cache >> __bits;
113      __bits_left -= __bits;
114      if (__bits_left < 32)
115        {
116          __cache |= ((uint64_t(_M_mt())) << __bits_left);
117          __bits_left += 32;
118        }
119      return __res;
120    }
121};
122
123} // namespace __gnu_parallel
124
125#endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */
126