Bit-magic division by 100

// div100 a 1000000
// div100 t 1000000

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

int div100(long long dividend) {
    const long long divisor = 0x28f5c29;
    return ((divisor * dividend) >> 32) & 0xffffffff;
}

//

unsigned long microseconds() {
    struct timeval tv;
    gettimeofday(&tv,NULL);
    return  1000000 * tv.tv_sec + tv.tv_usec;
}

void testCorrect(long long size) {
    int counter = 0;
        for (long long i = 0; i < size; i++) {
                int expected = i / 100;
                int value = div100(i);
                if (expected != value) {
                        printf("FAILED: %lld\t/ 100 = %d\t but value is %d\n", i, expected, value);
                        counter++;
                }
        }
    if (counter == 0)
        printf("Succuss\n");
    else
        printf("Failed %d times\n", counter);
}

void testTime(long long size) {
    unsigned long last, cur;

    last = microseconds();
    for (long long i = 0; i < size; i++) {
    int value = div100(i);
    }

    cur = microseconds();
    printf("Standart division: %ldµs\n", cur - last);

    last = microseconds();
    for (long long i = 0; i < size; i++) {
        int value = i / 100;
    }

    cur = microseconds();
    printf("Bit-magic division: %ldµs\n", cur - last);
}

int main(int argc, char **argv) {
    if (*argv[1] == 'a') { // Check results
        long long size = atoll(argv[2]);
        printf("Test correct: %lld\n", size);
        testCorrect(size);
    }
    else if (*argv[1] == 't') { // Check time
        long long size = atoll(argv[2]);
        printf("Test time: %lld\n", size);
        testTime(size);
    }
    else {
        printf("Unknown option: %c", *argv[1]);
    }
    return 0;
}