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/*
Copyright (c) 1990 Regents of the University of California.
All rights reserved.
*/
#define _DEFAULT_SOURCE
#include <stdlib.h>
/* Pseudo-random generator based on Minimal Standard by
Lewis, Goodman, and Miller in 1969.
I[j+1] = a*I[j] (mod m)
where a = 16807
m = 2147483647
Using Schrage's algorithm, a*I[j] (mod m) can be rewritten as:
a*(I[j] mod q) - r*{I[j]/q} if >= 0
a*(I[j] mod q) - r*{I[j]/q} + m otherwise
where: {} denotes integer division
q = {m/a} = 127773
r = m (mod a) = 2836
note that the seed value of 0 cannot be used in the calculation as
it results in 0 itself
*/
int
rand_r(unsigned int *seed)
{
long k;
long s = (long)(*seed);
if (s == 0)
s = 0x12345987;
k = s / 127773;
s = 16807 * (s - k * 127773) - 2836 * k;
if (s < 0)
s += 2147483647;
(*seed) = (unsigned int)s;
return (int)(s & RAND_MAX);
}
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