3 * $Id: lcrand.h,v 1.2 2000/07/02 15:21:20 mdw Exp $
5 * Simple linear congruential generator
7 * (c) 1999 Straylight/Edgeware
8 * (c) 2000 Mark Wooding
11 /*----- Licensing notice --------------------------------------------------*
13 * Copyright (c) 2000 Mark Wooding
14 * All rights reserved.
16 * Redistribution and use in source and binary forms, with or without
17 * modification, are permitted provided that the following conditions are
20 * 1. Redistributions of source code must retain the above copyright
21 * notice, this list of conditions and the following disclaimer.
23 * 2, Redistributions in binary form must reproduce the above copyright
24 * notice, this list of conditions and the following disclaimer in the
25 * documentation and/or other materials provided with the distribution.
27 * 3. The name of the authors may not be used to endorse or promote
28 * products derived from this software without specific prior written
31 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
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43 * Instead of accepting the above terms, you may redistribute and/or modify
44 * this software under the terms of either the GNU General Public License,
45 * or the GNU Library General Public License, published by the Free
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50 /*----- Revision history --------------------------------------------------*
53 * Revision 1.2 2000/07/02 15:21:20 mdw
56 * Revision 1.1 2000/05/21 11:28:30 mdw
59 * --- Past lives (Catacomb) --- *
61 * Revision 1.1 1999/12/10 23:15:27 mdw
62 * Noncryptographic random number generator.
66 /*----- Notes on the linear congruential generator ------------------------*
68 * This pseudorandom number generator is simple, but has absolutely no
69 * cryptographic strength whatever. It may be used whenever random numbers
70 * are required but cryptographic strength is not, for example when
71 * generating numbers for use in primality tests. To be honest, it's not
72 * even particularly fast, although a certain amount of effort has been
73 * expended on making it better than awfully slow. To put things in
74 * perspective, it can't quite spit bytes out as fast as OFB DES. (Then
75 * again, bytes aren't its natural output format.) Its main use is probably
76 * seeding a Fibonacci generator.
78 * There exists a fixed-point input @LCRAND_FIXEDPT@ -- when fed to the
79 * generator it comes straight back out again. All other inputs less than
80 * the modulus are part of the same sequence of period %$p - 1$%.
82 * The generator has been tested for its statistical properties. George
83 * Marsaglia's Diehard tests give it a reasonably clean bill of health.
85 * The modulus %$p$% is chosen as the largest prime number less than
86 * %$2^{32}$%. The multiplier %$a$% and additive constant %$c$% are based on
87 * the decimal expansions of %$\pi$% and %$e$%, with the additional
88 * restriction that the multiplier must be a primitive element modulo %$p$%.
89 * The fixed point value is determined as %$c / (1 - a) \bmod p$%.
99 /*----- Header files ------------------------------------------------------*/
105 /*----- Constants ---------------------------------------------------------*/
107 #define LCRAND_P 4294967291u /* Modulus for the generator */
108 #define LCRAND_A 314159265u /* Multiplier (primitive mod @p@) */
109 #define LCRAND_C 271828183u /* Additive constant */
111 #define LCRAND_FIXEDPT 3223959250u /* Fixed point (only bad input) */
113 /*----- Functions provided ------------------------------------------------*/
115 /* --- @lcrand@ --- *
117 * Arguments: @uint32 x@ = seed value
119 * Returns: New state of the generator.
121 * Use: Steps the generator. Returns %$ax + c \bmod p$%.
124 extern uint32 lcrand(uint32 /*x*/);
126 /* --- @lcrand_range@ --- *
128 * Arguments: @uint32 *x@ = pointer to seed value (updated)
129 * @uint32 m@ = limit allowable
131 * Returns: A uniformly distributed pseudorandom integer in the interval
135 extern uint32 lcrand_range(uint32 */*x*/, uint32 /*m*/);
137 /*----- That's all, folks -------------------------------------------------*/