uniqueness test for Linear congruential generator

uniq_test.c

#include <stdio.h>
#include <time.h>

#define NSUB (1L<<32)
#define NBIT 48
//#define NSUB (1<<4)
//#define NBIT 8
#define COUNT(isub, iseg) (isub*((long)NSUB)+iseg)
#define PRINT_COUNT(msg, count) printf("%s: iSub= %ld\tcount= %ld\tr1= %ld\tr2=%ld\telapse= %f\n", msg, isub, count, r1, r2, elapse)
#define PRINT(msg) PRINT_COUNT(msg, COUNT(isub, iseg))

typedef long index_t;

long random_next(long seed) {
	return  (seed * 0x5DEECE66DL + 0xBL) & ((1L << NBIT) - 1);
}

clock_t start_timer() {
	return clock();
}
clock_t duration_timer(start_clock) {
	return ((double) (clock() - start_clock)) / CLOCKS_PER_SEC;
}

int main() {
	long seed = 1;
	long r1;
	long r2;
	index_t isub;
	index_t iseg;
	long count_all = 0;
	double elapse = 0;

	// first loop to detect loop
	isub = 0;
	r1 = seed;
	r2 = seed;
	while (1) {
		clock_t start = start_timer();
		iseg=0;
		while (iseg<NSUB) {
			r1 = random_next(r1);
			r2 = random_next(random_next(r2));
			if (r1 == r2) break;
			iseg++;
		}
		if (r1 == r2) break;
		elapse += duration_timer(start);
		PRINT("PROC1");
		isub++;
	}
	count_all += COUNT(isub, iseg);
	PRINT("FND1");

	// if meet point is a seed, which means "complete circlular",
	// no need to second loop.
	if (r1 == seed) goto done;

	// Second loop to find start of loop
	isub = 0;
	r2 = seed;
	while (1) {
		clock_t start = start_timer();
		iseg=0;
		while (iseg<NSUB) {
			r1 = random_next(r1);
			r2 = random_next(r2);
			if (r1 == r2) break;
			iseg++;
		}
		if (r1 == r2) break;
		elapse += duration_timer(start);
		PRINT("PROC2");
		isub++;
	}
	count_all += COUNT(isub, iseg);
	PRINT("FND2");

done:
	PRINT_COUNT("DONE", count_all);
	return 0;
}