ranny.c   [plain text]

/*
 * Random number generator is:
 *
 *	Copyright 1988 by Rayan S. Zachariassen, all rights reserved.
 *	This will be free software, but only when it is finished.
 *
 * Used in ntp by permission of the author.  If copyright is
 * annoying to you, read no further.  Instead, look up the reference,
 * write me an equivalent to this and send it back to me.
 */

/*
 * Random number generator; see Knuth Vol 2. 2nd ed. p.27 (section 3.2.2)
 */
#include "ntp_stdlib.h"

extern	time_t	time		P((time_t *loc));

/*
 * 55 random numbers, not all even.  Note we don't initialize ran_y
 * directly since I have had thoughts of putting this in an EPROM
 */
static time_t ran_y[55];

static time_t init_ran_y[55] = {
	1860909544, 231033423, 437666411, 1349655137, 2014584962,
	504613712, 656256107, 1246027206, 573713775, 643466871,
	540235388, 1630565153, 443649364, 729302839, 1933991552,
	944681982, 949111118, 406212522, 1065063137, 1712954727,
	73280612, 787623973, 1874130997, 801658492, 73395958,
	739165367, 596047144, 490055249, 1131094323, 662727104,
	483614097, 844520219, 893760527, 921280508, 46691708,
	760861842, 1425894220, 702947816, 2006889048, 1999607995,
	1346414687, 399640789, 1482689501, 1790064052, 1128943628,
	1269197405, 587262386, 2078054746, 1675409928, 1652325524,
	1643525825, 1748690540, 292465849, 1370173174, 402865384
};

static int ran_j;
static int ran_k;


/*
 * ranp2 - return a random integer in the range 0 .. (1 << m) - 1
 */
u_long
ranp2(
	int m
	)
{
	time_t r;

	ran_y[ran_k] += ran_y[ran_j];	/* overflow does a mod */
	r = ran_y[ran_k];
	if (ran_k-- == 0)
	    ran_k = 54;
	if (ran_j-- == 0)
	    ran_j = 54;
	return (u_long)(r & ((1 << m ) - 1));
}

/*
 * init_random - do initialization of random number routine
 */
void
init_random(void)
{
	register int i;
	register time_t now;

	ran_j = 23;
	ran_k = 54;

	/*
	 * Randomize the seed array some more.  The time of day
	 * should be initialized by now.
	 */
	now = time((time_t *)0) | 01;

	for (i = 0; i < 55; ++i)
	    ran_y[i] = now * init_ran_y[i];	/* overflow does a mod */
}