#include <stdio.h>
#include <time.h>
#include <sys/time.h>
// Ivan Novick, May 16, 2009
// gcc time_test.c -o time_test -lrt

#define NUM_TESTS 10000000

struct timespec diff_timespec(struct timespec start, struct timespec end);
long long microsec_elapsed(struct timespec diff);

int main(int argc, char** argv){

    struct timespec start;
    struct timespec end;
    struct timespec diff;
    long long i;

    time_t tmp1;
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 1; i < NUM_TESTS; ++i){
        tmp1 = time(NULL);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("time function took:         %.3f microseconds on average\n", (double)microsec_elapsed(diff)/NUM_TESTS);

    struct timeval tmp2;
    clock_gettime(CLOCK_MONOTONIC, &start);
    for (i = 1; i < NUM_TESTS; ++i){
        gettimeofday(&tmp2, NULL);
    }
    clock_gettime(CLOCK_MONOTONIC, &end);
    diff = diff_timespec(start, end);
    printf("gettimeofday function took: %.3f microseconds on average\n", (double)microsec_elapsed(diff)/NUM_TESTS);

    return 0;
}

struct timespec diff_timespec(struct timespec start, struct timespec end)
{
    struct timespec result;

    if (end.tv_nsec < start.tv_nsec){ // peform carry like in normal subtraction
        //                123456789
        result.tv_nsec = 1000000000 + end.tv_nsec - start.tv_nsec;        
        result.tv_sec = end.tv_sec - 1 - start.tv_sec;
    }
    else{
        result.tv_nsec = end.tv_nsec - start.tv_nsec;        
        result.tv_sec = end.tv_sec - start.tv_sec;
    }

    return result;
}

long long microsec_elapsed(struct timespec diff){
    //                                123456                     123
    return ((long long)diff.tv_sec * 1000000) + (diff.tv_nsec / 1000);
}