#ifndef lint
static const char	RCSid[] = "$Id: urand.c,v 2.5 2003/02/22 02:07:22 greg Exp $";
#endif
/*
 * Anticorrelated random function due to Christophe Schlick
 */

/* ====================================================================
 * The Radiance Software License, Version 1.0
 *
 * Copyright (c) 1990 - 2002 The Regents of the University of California,
 * through Lawrence Berkeley National Laboratory.   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 end-user documentation included with the redistribution,
 *           if any, must include the following acknowledgment:
 *             "This product includes Radiance software
 *                 (http://radsite.lbl.gov/)
 *                 developed by the Lawrence Berkeley National Laboratory
 *               (http://www.lbl.gov/)."
 *       Alternately, this acknowledgment may appear in the software itself,
 *       if and wherever such third-party acknowledgments normally appear.
 *
 * 4. The names "Radiance," "Lawrence Berkeley National Laboratory"
 *       and "The Regents of the University of California" must
 *       not be used to endorse or promote products derived from this
 *       software without prior written permission. For written
 *       permission, please contact radiance@radsite.lbl.gov.
 *
 * 5. Products derived from this software may not be called "Radiance",
 *       nor may "Radiance" appear in their name, without prior written
 *       permission of Lawrence Berkeley National Laboratory.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED 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 Lawrence Berkeley National Laboratory OR
 * ITS 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.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of Lawrence Berkeley National Laboratory.   For more
 * information on Lawrence Berkeley National Laboratory, please see
 * <http://www.lbl.gov/>.
 */

#include  <stdlib.h>
#include  "random.h"

#undef initurand

#define  MAXORDER	(8*sizeof(unsigned short))

unsigned short  *urperm = NULL;	/* urand() permutation */
int  urmask;		/* bits used in permutation */

int
initurand(size)		/* initialize urand() for size entries */
int  size;
{
	int  order, n;
	register int  i, offset;

	if (urperm != NULL)
		free((void *)urperm);
	if (--size <= 0) {
		urperm = NULL;
		urmask = 0;
		return(0);
	}
	for (i = 1; size >>= 1; i++)
		;
	order = i>MAXORDER ? MAXORDER : i;
	urmask = (1<<i) - 1;
	urperm = (unsigned short *)malloc((urmask+1)*sizeof(unsigned short));
	if (urperm == NULL) {
		eputs("out of memory in initurand\n");
		quit(1);
	}
	urperm[0] = 0;
	for (n = 1, offset = 1; n <= order; n++, offset <<= 1)
		for (i = offset; i--; ) {
			urperm[i] =
			urperm[i+offset] = 2*urperm[i];
			if (random() & 0x4000)
				urperm[i]++;
			else
				urperm[i+offset]++;
		}
	return(1<<order);
}


int
ilhash(d, n)			/* hash a set of integer values */
register int  *d;
register int  n;
{
	static int  tab[8] = {13623,353,1637,5831,2314,3887,5832,8737};
	register int  hval;

	hval = 0;
	while (n-- > 0)
		hval += *d++ * tab[n&7];
	return(hval);
}