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

// interval timing functions used to do performance testing of some sorts
// these functions used to use gettimeofday which is not the correct way to
// do this: search on google gettimeofday clock_gettime
// originally written Nov-2007, revised Mar-2009

// compile and link as follows:
// gcc elapsed.c -o elapsed -lrt

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

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

long long nanosec_elapsed(struct timespec diff){
    //                                123456789
    return ((long long)diff.tv_sec * 1000000000) + diff.tv_nsec;
}

int main(int argc, char** argv)
{
    struct timespec start;
    struct timespec end;
    struct timespec diff;
    int i;

    clock_gettime(CLOCK_MONOTONIC, &start);

    for (i = 0 ; i < 1234567; ++i)
    {
        fprintf(stderr, "%d\n", i);
    }

    clock_gettime(CLOCK_MONOTONIC, &end);

    diff = diff_timespec(start, end);

    printf("operations took %lld milliseconds\n", millisec_elapsed(diff));
    printf("operations took %lld microseconds\n", microsec_elapsed(diff));
    printf("operations took %lld nanoseconds\n", nanosec_elapsed(diff));

    return 0;
}