stochastik_ws19_nr2.c

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

// Must be a multiply of 8
const int TOTAL = 1000000;

int main() {
    struct timespec start;
    clock_gettime(CLOCK_REALTIME, &start);

    // Seed the random generator
    srand(time(NULL));
    
    int sum = 0;
    // In each iteration of the loop we get 8 random pairs, so we
    // run the loop only TOTAL/8 times.
    for (int i = 0; i < TOTAL / 8; i++) {
        int rand_value = rand();

        for (int j = 0; j < 8; j++) {
            // Take 4 bit from the random value for 8 times.
            // This results in 32 bit which is the size of an int.

            // First random value are the lower 2 bits
            int r1 = (rand_value & 0b11);
            rand_value >>= 2;
            // Second random value are the higher 2 bits
            int r2 = (rand_value & 0b11);
            rand_value >>= 2;

            if (r1 == r2) {
                sum++;
            }
        }
        sum += rand_value;
    }
    double probability = (double)sum / TOTAL;
    struct timespec end;
    clock_gettime(CLOCK_REALTIME, &end);

    printf("Probability %f\n", probability);
    printf("%lus %fms\n", end.tv_sec-start.tv_sec, (double)(end.tv_nsec - start.tv_nsec)/1e6);
    return 0;
}