07871354 |
1 | /* -*-c-*- |
2 | * |
b817bfc6 |
3 | * $Id: lcrand.h,v 1.3 2004/04/08 01:36:15 mdw Exp $ |
07871354 |
4 | * |
5 | * Simple linear congruential generator |
6 | * |
7 | * (c) 1999 Straylight/Edgeware |
8 | */ |
9 | |
10 | /*----- Licensing notice --------------------------------------------------* |
11 | * |
12 | * This file is part of Catacomb. |
13 | * |
14 | * Catacomb is free software; you can redistribute it and/or modify |
15 | * it under the terms of the GNU Library General Public License as |
16 | * published by the Free Software Foundation; either version 2 of the |
17 | * License, or (at your option) any later version. |
18 | * |
19 | * Catacomb is distributed in the hope that it will be useful, |
20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
22 | * GNU Library General Public License for more details. |
23 | * |
24 | * You should have received a copy of the GNU Library General Public |
25 | * License along with Catacomb; if not, write to the Free |
26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
27 | * MA 02111-1307, USA. |
28 | */ |
29 | |
07871354 |
30 | /*----- Notes on the linear congruential generator ------------------------* |
31 | * |
32 | * This pseudorandom number generator is simple, but has absolutely no |
33 | * cryptographic strength whatever. It may be used whenever random numbers |
34 | * are required but cryptographic strength is not, for example when |
35 | * generating numbers for use in primality tests. To be honest, it's not |
36 | * even particularly fast, although a certain amount of effort has been |
bc4c10df |
37 | * expended on making it better than awfully slow. To put things in |
38 | * perspective, it can't quite spit bytes out as fast as OFB DES. (Then |
39 | * again, bytes aren't its natural output format.) Its main use is probably |
40 | * seeding a Fibonacci generator. |
07871354 |
41 | * |
42 | * There exists a fixed-point input @LCRAND_FIXEDPT@ -- when fed to the |
43 | * generator it comes straight back out again. All other inputs less than |
44 | * the modulus are part of the same sequence of period %$p - 1$%. |
45 | * |
46 | * The generator has been tested for its statistical properties. George |
47 | * Marsaglia's Diehard tests give it a reasonably clean bill of health. |
48 | * |
49 | * The modulus %$p$% is chosen as the largest prime number less than |
50 | * %$2^{32}$%. The multiplier %$a$% and additive constant %$c$% are based on |
51 | * the decimal expansions of %$\pi$% and %$e$%, with the additional |
52 | * restriction that the multiplier must be a primitive element modulo %$p$%. |
53 | * The fixed point value is determined as %$c / (1 - a) \bmod p$%. |
54 | */ |
55 | |
bc4c10df |
56 | #ifndef CATACOMB_LCRAND_H |
57 | #define CATACOMB_LCRAND_H |
58 | |
59 | #ifdef __cplusplus |
60 | extern "C" { |
61 | #endif |
62 | |
07871354 |
63 | /*----- Header files ------------------------------------------------------*/ |
64 | |
65 | #include <mLib/bits.h> |
66 | |
67 | #ifndef CATACOMB_GRAND_H |
68 | # include "grand.h" |
69 | #endif |
70 | |
71 | /*----- Constants ---------------------------------------------------------*/ |
72 | |
73 | #define LCRAND_P 4294967291u /* Modulus for the generator */ |
74 | #define LCRAND_A 314159265u /* Multiplier (primitive mod @p@) */ |
75 | #define LCRAND_C 271828183u /* Additive constant */ |
76 | |
77 | #define LCRAND_FIXEDPT 3223959250u /* Fixed point (only bad input) */ |
78 | |
79 | /*----- Functions provided ------------------------------------------------*/ |
80 | |
81 | /* --- @lcrand@ --- * |
82 | * |
83 | * Arguments: @uint32 x@ = seed value |
84 | * |
85 | * Returns: New state of the generator. |
86 | * |
87 | * Use: Steps the generator. Returns %$ax + c \bmod p$%. |
88 | */ |
89 | |
90 | extern uint32 lcrand(uint32 /*x*/); |
91 | |
92 | /* --- @lcrand_range@ --- * |
93 | * |
94 | * Arguments: @uint32 *x@ = pointer to seed value (updated) |
95 | * @uint32 m@ = limit allowable |
96 | * |
97 | * Returns: A uniformly distributed pseudorandom integer in the interval |
98 | * %$[0, m)$%. |
99 | */ |
100 | |
101 | extern uint32 lcrand_range(uint32 */*x*/, uint32 /*m*/); |
102 | |
103 | /* --- @lcrand_create@ --- * |
104 | * |
105 | * Arguments: @uint32 x@ = initial seed |
106 | * |
107 | * Returns: Pointer to a generic generator. |
108 | * |
109 | * Use: Constructs a generic generator interface over a linear |
110 | * congruential generator. |
111 | */ |
112 | |
113 | extern grand *lcrand_create(uint32 /*x*/); |
114 | |
115 | /*----- That's all, folks -------------------------------------------------*/ |
116 | |
117 | #ifdef __cplusplus |
118 | } |
119 | #endif |
120 | |
121 | #endif |