Arduino LCG play-set

test.c

#include <stdlib.h>
#include <stdio.h>

static int do_rand(unsigned long *ctx)
{
	/*
	 * Compute x = (7^5 * x) mod (2^31 - 1)
	 * wihout overflowing 31 bits:
	 *      (2^31 - 1) = 127773 * (7^5) + 2836
	 * From "Random number generators: good ones are hard to find",
	 * Park and Miller, Communications of the ACM, vol. 31, no. 10,
	 * October 1988, p. 1195.
	 */
	long hi, lo, x;

	x = *ctx;
	/* Can't be initialized with 0, so use another value. */
	if (x == 0)
		x = 123459876L;
	hi = x / 127773L;
	lo = x % 127773L;
	x = 16807L * lo - 2836L * hi;
	if (x < 0)
		x += 0x7fffffffL;
	return ((*ctx = x) % ((unsigned long)RAND_MAX + 1));
}

static unsigned long next = 1;

int rand(void)
{
	return do_rand(&next);
}

void srand(unsigned int seed)
{
	next = seed;
}


int main(int argc, char **argv)
{
	char *p;
	long conv = strtol(argv[1], &p, 10);
	srand(conv); // seed with input
	unsigned long start = rand(); // get starting number
        if ((start & 0xffff) == 0){
		      printf("%04x\n", start);
        }

	long unsigned int t;
	//for (int i=0; i<8000000; i++) {
	while(1){
		t = rand();
		if (t == start){
			printf("We are done!");
			return 0;
		}
		if ((t & 0xffff) == 0){
			printf("%04x\n", t);
		}
	}

}