/* -*-c-*-
*
* $Id: lcrand.h,v 1.3 2004/04/08 01:36:15 mdw Exp $
*
* Simple linear congruential generator
*
* (c) 1999 Straylight/Edgeware
*/
/*----- Licensing notice --------------------------------------------------*
*
* This file is part of Catacomb.
*
* Catacomb is free software; you can redistribute it and/or modify
* it under the terms of the GNU Library General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* Catacomb is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Library General Public License for more details.
*
* You should have received a copy of the GNU Library General Public
* License along with Catacomb; if not, write to the Free
* Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
* MA 02111-1307, USA.
*/
/*----- Notes on the linear congruential generator ------------------------*
*
* This pseudorandom number generator is simple, but has absolutely no
* cryptographic strength whatever. It may be used whenever random numbers
* are required but cryptographic strength is not, for example when
* generating numbers for use in primality tests. To be honest, it's not
* even particularly fast, although a certain amount of effort has been
* expended on making it better than awfully slow. To put things in
* perspective, it can't quite spit bytes out as fast as OFB DES. (Then
* again, bytes aren't its natural output format.) Its main use is probably
* seeding a Fibonacci generator.
*
* There exists a fixed-point input @LCRAND_FIXEDPT@ -- when fed to the
* generator it comes straight back out again. All other inputs less than
* the modulus are part of the same sequence of period %$p - 1$%.
*
* The generator has been tested for its statistical properties. George
* Marsaglia's Diehard tests give it a reasonably clean bill of health.
*
* The modulus %$p$% is chosen as the largest prime number less than
* %$2^{32}$%. The multiplier %$a$% and additive constant %$c$% are based on
* the decimal expansions of %$\pi$% and %$e$%, with the additional
* restriction that the multiplier must be a primitive element modulo %$p$%.
* The fixed point value is determined as %$c / (1 - a) \bmod p$%.
*/
#ifndef CATACOMB_LCRAND_H
#define CATACOMB_LCRAND_H
#ifdef __cplusplus
extern "C" {
#endif
/*----- Header files ------------------------------------------------------*/
#include
#ifndef CATACOMB_GRAND_H
# include "grand.h"
#endif
/*----- Constants ---------------------------------------------------------*/
#define LCRAND_P 4294967291u /* Modulus for the generator */
#define LCRAND_A 314159265u /* Multiplier (primitive mod @p@) */
#define LCRAND_C 271828183u /* Additive constant */
#define LCRAND_FIXEDPT 3223959250u /* Fixed point (only bad input) */
/*----- Functions provided ------------------------------------------------*/
/* --- @lcrand@ --- *
*
* Arguments: @uint32 x@ = seed value
*
* Returns: New state of the generator.
*
* Use: Steps the generator. Returns %$ax + c \bmod p$%.
*/
extern uint32 lcrand(uint32 /*x*/);
/* --- @lcrand_range@ --- *
*
* Arguments: @uint32 *x@ = pointer to seed value (updated)
* @uint32 m@ = limit allowable
*
* Returns: A uniformly distributed pseudorandom integer in the interval
* %$[0, m)$%.
*/
extern uint32 lcrand_range(uint32 */*x*/, uint32 /*m*/);
/* --- @lcrand_create@ --- *
*
* Arguments: @uint32 x@ = initial seed
*
* Returns: Pointer to a generic generator.
*
* Use: Constructs a generic generator interface over a linear
* congruential generator.
*/
extern grand *lcrand_create(uint32 /*x*/);
/*----- That's all, folks -------------------------------------------------*/
#ifdef __cplusplus
}
#endif
#endif