libstdc++
random_number.h
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1 // -*- C++ -*-
2 
3 // Copyright (C) 2007, 2008, 2009 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 
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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 
39 namespace __gnu_parallel
40 {
41  /** @brief Random number generator, based on the Mersenne twister. */
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,
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. */
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
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 */