contrib/xntpd/lib/ranny.c

/* ranny.c,v 3.1 1993/07/06 01:08:43 jbj Exp
 * 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 xntp 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 U_LONG ran_y[55];

static U_LONG 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(m)
        int m;
{
        U_LONG 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 (r & ((1<<m)-1));
}

#ifdef notdef
/*
 * ranny - return a random integer in the range 0 .. m-1
 */
U_LONG
ranny(m)
        u_int m;
{
        unsigned LONG 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 (r % m);
}
#endif /* notdef */

/*
 * init_random - do initialization of random number routine
 */
void
init_random()
{
        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_t)(time((time_t *)0))|01;

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