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[storin] / fibrand.h

/* -*-c-*-
 *
 * $Id: fibrand.h,v 1.1 2000/05/21 11:28:30 mdw Exp $
 *
 * Fibonacci 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: fibrand.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 Fibonacci generator ----------------------------------*
 *
 * The generator was originally suggested by G. J. Mitchell and D. P. Moore
 * in 1957, and publicized by D. E. Knuth as Algorithm 3.2.2A in volume 2 of
 * his work `The Art of Computer Programming'.  The generator is simple: at
 * each stage it emits %$x_n = (x_{n - 55} + x_{n - 24}) \bmod 2^{32}$%.  The
 * period is proven to be greater than %$2^{55}$%, and statistical properties
 * appear to be good.
 */

#ifndef FIBRAND_H
#define FIBRAND_H

#ifdef __cplusplus
  extern "C" {
#endif

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

#ifndef BITS_H
#  include "bits.h"
#endif

/*----- Magic constants ---------------------------------------------------*/

#define FIB_SZ 55
#define FIB_TAP 24

/*----- Data structures ---------------------------------------------------*/

typedef struct fibrand {
  unsigned i;
  uint32 x[FIB_SZ];
} fibrand;

/*----- Functions provided ------------------------------------------------*/

/* --- @fibrand_step@ --- *
 *
 * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
 *
 * Returns:	Next output from generator.
 *
 * Use:		Steps the generator.  Returns
 *		%$x_{i - 24} + x_{i - 55} \bmod 2^{32}$%.
 */

extern uint32 fibrand_step(fibrand */*f*/);

/* --- @fibrand_lcseed@ --- *
 *
 * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
 *		@uint32 seed@ = seed value
 *
 * Returns:	---
 *
 * Use:		Initializes a Fibonacci generator using outputs from the
 *		@lcrand@ generator seeded from @seed@.  This is faster than
 *		using a generic @lcrand@-based generator and @fibrand_rseed@
 *		because it uses raw outputs rather than uniformly distributed
 *		32-bit words.
 */

extern void fibrand_lcseed(fibrand */*f*/, uint32 /*seed*/);

/* --- @fibrand_range@ --- *
 *
 * Arguments:	@fibrand *f@ = pointer to Fibonacci generator context
 *		@uint32 m@ = limit
 *
 * Returns:	A uniformly distributed pseudorandom integer in the interval
 *		%$[0, m)$%.
 */

extern uint32 fibrand_range(fibrand */*f*/, uint32 /*m*/);

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

#ifdef __cplusplus
  }
#endif

#endif