Initial check-in.

[storin] / fibrand.c

/* -*-c-*-
 *
 * $Id: fibrand.c,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.c,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.
 *
 */

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

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "bits.h"
#include "fibrand.h"
#include "lcrand.h"

/*----- Main code ---------------------------------------------------------*/

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

uint32 fibrand_step(fibrand *f)
{
  unsigned i = f->i;
  unsigned j = i + (FIB_SZ - FIB_TAP);
  uint32 x;
  if (j >= FIB_SZ)
    j -= FIB_SZ;
  x = f->x[i] = U32(f->x[i] + f->x[j]);
  i++;
  if (i >= FIB_SZ)
    i = 0;
  f->i = i;
  return (x);
}

/* --- @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.
 */

void fibrand_lcseed(fibrand *f, uint32 seed)
{
  int i;
  unsigned p = 0;

  for (i = 0; i < FIB_SZ; i++)
    p |= f->x[i] = seed = lcrand(seed);
  if (!(p & 1)) {
    i = lcrand_range(&seed, FIB_SZ);
    f->x[i] |= 1;
  }
  f->i = 0;
}

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

uint32 fibrand_range(fibrand *f, uint32 m)
{
  uint32 r = 0xffffffff - (0xffffffff % m);
  uint x;

  /* --- Now generate numbers until a good one comes along --- */

  do x = fibrand_step(f); while (x >= r);
  return (x / (r / m));
}

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