Measure the distance between milliseconds using div and milliseconds using shift

measure_distance_get_milliseconds.c

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

long get_milliseconds_using_div(void)
{
    struct timespec tp;
    clock_gettime(CLOCK_REALTIME, &tp);
    return ((tp.tv_sec * 1000) + (tp.tv_nsec / 1000000L));
}

long get_milliseconds_using_shift(void)
{
    struct timespec tp;
    clock_gettime(CLOCK_REALTIME, &tp);
    return ((tp.tv_sec << 10) | (tp.tv_nsec >> 20));
}

void measure_distance()
{
        long div = get_milliseconds_using_div();
        long shift = get_milliseconds_using_shift();
        
        printf("timestamp using div:   %ld ms\n", div);
        printf("timestamp using shift: %ld ms\n", shift);
        printf("distance in seconds:   %ld s\n", (shift - div) / 1000);
        printf("distance in days:      %ld days\n", (shift - div) / 1000 / 60 / 60 / 24);
}

int main()
{
    measure_distance(); // measure the difference between timestamps TODAY
}

OUTPUT:

user@computer:~$ gcc -O0 measure_distance_get_milliseconds.c && ./a.out 
timestamp using div:   1691404335877 ms
timestamp using shift: 1731998039876 ms
distance in seconds:   40593703 s
distance in days:      469 days