libstdc++

random_number.h
Go to the documentation of this file.
1 // -*- C++ -*-
2
3 // Copyright (C) 2007-2013 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
39 namespace __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 */