/* Ivan Novick
   This code is completely free to be used by anyone for any purpose.
   April 7, 2010
   gettimeofday_diff.c
*/

#include <stdio.h>
#include <sys/time.h>
#include <unistd.h> /* required for testcode only not for micros_elapsed function */

unsigned int micros_elapsed (struct timeval *begin, struct timeval *end)
{
    const unsigned int million = 1000000;

    unsigned int result;
    unsigned int end_tv_sec;
    unsigned int end_tv_usec;

    /* do the carry */
    if (end->tv_usec < begin->tv_usec)
    {
        end_tv_sec = end->tv_sec - 1;
        end_tv_usec = end->tv_usec + million;
    }
    else
    {
        end_tv_sec = end->tv_sec;
        end_tv_usec = end->tv_usec;
    }

    result = end_tv_sec - begin->tv_sec;
    result *= million;
    result += (end_tv_usec - begin->tv_usec);

    return result;
}    


int main(int argc, char** argv)
{
    const unsigned int million = 1000000;
    struct timeval begin;
    struct timeval end;
    unsigned int elapsed;
    unsigned int testsleep = million;

    while (1)
    {
        printf("sleep   = %d micros\n", testsleep);

        gettimeofday(&begin, NULL);
        usleep(testsleep);
        gettimeofday(&end, NULL);

        elapsed = micros_elapsed(&begin, &end);
        printf("elapsed = %d micros\n\n", elapsed);

        /* gradually adjust sleep so it sometimes is below 1 second and sometimes above
            the purpose is to verify the carry code in the subtraction is working fine */
        if (elapsed < million)
        {
            testsleep += 5;
        }
        else
        {
            testsleep -= 5;
        }
    }

    return 0;
}