🚀 go-pugleaf

#include <stdio.h>

/* This file implements the "minimal standard" RNG
   from the paper "RNGs: Good Ones are Hard to Find" by Park and
   Miller, CACM, Volume 31, Number 10, October 1988. */

static long int seed = 1;
/* static so programs will be more "orderly" in modifying the
   seed.  The setseed function is the prescribed way in which the seed
   is altered.  A good default to use is your SSN.
   Any seed from 1 to 2147483646 is equally ok. */

int setseed(long int newseed)
{
    if ((newseed < 1) || (newseed > 2147483646)) return 1;
    seed = newseed; return 0;
}

double ranpm()
     /* page 1195-right, "Integer Version 2", works iff ints are 32 bits.*/
{
    long int a=16807, m=2147483647, q=127773, r=2836;
    int lo, hi, test;

    hi = seed / q;
    lo = seed % q;
    test = a * lo - r * hi;
    seed = (test > 0) ? test : test + m;
    return (seed/ (double) m);
}

#ifdef TESTING
/* They give us one test (on page 1195-left): if seed = 1 then
   the 10001'th random number should be 1043618065.
   Apart from this, I do some superficial testing aimed at checking
   the code above is not buggy.  I'm not trying to test the
   statistical properties of the RNG. */

int main()
{
    int n; double u, sum=0.0, sum2=0.0;
    
    for (n=1; n<=10000; n++) {
	u = ranpm();
	if ((u < 0.0) || (u > 1.0)) {
	    printf("Garbage at the %dth number!\n");
	    return 1;
	}
	sum += u;
	sum2 += (u*u);
    }
    printf("The current value of seed is : %10d\n", seed);
    printf("The Truth is %17s 1043618065\n\n", " ");

    printf("Mean of 1st 10k nums is %f, variance is %f\n",
	   sum/10000, sum2/9999);
    printf("Expect .5018 and .3355\n");
    return 0;
}
#endif /* TESTING */
-- 
Ajay Shah, (213)749-8133, ajayshah@usc.edu