freebsd-dev/contrib/ntp/libntp/ranny.c

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1999-12-09 13:01:21 +00:00
/*
* 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 */
}