Initial check-in.

[storin] / lcrand.h

/* -*-c-*-
 *
 * $Id: lcrand.h,v 1.1 2000/05/21 11:28:30 mdw Exp $
 *
 * Simple linear congruential generator
 *
 * (c) 1999 Straylight/Edgeware
 * (c) 2000 Mark Wooding
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * Copyright (c) 2000 Mark Wooding
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 
 * 2, Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 
 * 3. The name of the authors may not be used to endorse or promote
 *    products derived from this software without specific prior written
 *    permission.
 * 
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN
 * NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
 * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 * 
 * Instead of accepting the above terms, you may redistribute and/or modify
 * this software under the terms of either the GNU General Public License,
 * or the GNU Library General Public License, published by the Free
 * Software Foundation; either version 2 of the License, or (at your
 * option) any later version.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: lcrand.h,v $
 * Revision 1.1  2000/05/21 11:28:30  mdw
 * Initial check-in.
 *
 * --- Past lives (Catacomb) --- *
 *
 * Revision 1.1  1999/12/10 23:15:27  mdw
 * Noncryptographic random number generator.
 *
 */

/*----- 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 LCRAND_H
#define LCRAND_H

#ifdef __cplusplus
  extern "C" {
#endif

/*----- Header files ------------------------------------------------------*/

#ifndef BITS_H
#  include "bits.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*/);

/*----- That's all, folks -------------------------------------------------*/

#ifdef __cplusplus
  }
#endif

#endif