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
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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 
38 namespace __gnu_parallel
39 {
40  /** @brief Random number generator, based on the Mersenne twister. */
42  {
43  private:
45  uint64 supremum;
46  uint64 RAND_SUP;
47  double supremum_reciprocal;
48  double RAND_SUP_REC;
49 
50  // Assumed to be twice as long as the usual random number.
51  uint64 cache;
52 
53  // Bit results.
54  int bits_left;
55 
56  static uint32
57  scale_down(uint64 x,
59  uint64 /*supremum*/, double supremum_reciprocal)
60 #else
61  uint64 supremum, double /*supremum_reciprocal*/)
62 #endif
63  {
64 #if _GLIBCXX_SCALE_DOWN_FPU
65  return uint32(x * supremum_reciprocal);
66 #else
67  return static_cast<uint32>(x % supremum);
68 #endif
69  }
70 
71  public:
72  /** @brief Default constructor. Seed with 0. */
74  : mt(0), supremum(0x100000000ULL),
75  RAND_SUP(1ULL << (sizeof(uint32) * 8)),
76  supremum_reciprocal(double(supremum) / double(RAND_SUP)),
77  RAND_SUP_REC(1.0 / double(RAND_SUP)),
78  cache(0), bits_left(0) { }
79 
80  /** @brief Constructor.
81  * @param seed Random seed.
82  * @param supremum Generate integer random numbers in the
83  * interval @c [0,supremum). */
84  random_number(uint32 seed, uint64 supremum = 0x100000000ULL)
85  : mt(seed), supremum(supremum),
86  RAND_SUP(1ULL << (sizeof(uint32) * 8)),
87  supremum_reciprocal(double(supremum) / double(RAND_SUP)),
88  RAND_SUP_REC(1.0 / double(RAND_SUP)),
89  cache(0), bits_left(0) { }
90 
91  /** @brief Generate unsigned random 32-bit integer. */
92  uint32
94  { return scale_down(mt(), supremum, supremum_reciprocal); }
95 
96  /** @brief Generate unsigned random 32-bit integer in the
97  interval @c [0,local_supremum). */
98  uint32
99  operator()(uint64 local_supremum)
100  {
101  return scale_down(mt(), local_supremum,
102  double(local_supremum * RAND_SUP_REC));
103  }
104 
105  /** @brief Generate a number of random bits, run-time parameter.
106  * @param bits Number of bits to generate. */
107  unsigned long
108  genrand_bits(int bits)
109  {
110  unsigned long res = cache & ((1 << bits) - 1);
111  cache = cache >> bits;
112  bits_left -= bits;
113  if (bits_left < 32)
114  {
115  cache |= ((uint64(mt())) << bits_left);
116  bits_left += 32;
117  }
118  return res;
119  }
120 };
121 
122 } // namespace __gnu_parallel
123 
124 #endif /* _GLIBCXX_PARALLEL_RANDOM_NUMBER_H */