nix-public-expressions/rand/main.c

#define _POSIX_C_SOURCE 200809L

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

/**
 * Return a random number between 0 and limit inclusive.
 *
 */
int rand_lim(int limit) {

    int divisor = RAND_MAX/(limit+1);
    int retval;

    do { 
        retval = rand() / divisor;
    } while (retval > limit);

    return retval;
}

void print_current_time_with_ms (void) {
    long            ms; // Milliseconds
    time_t          s;  // Seconds
    struct timespec spec;

    clock_gettime(CLOCK_REALTIME, &spec);

    s  = spec.tv_sec;
    ms = round(spec.tv_nsec / 1.0e6); // Convert nanoseconds to milliseconds

    printf  ( "Current time: %ld.%03ld seconds since the Epoch\n"
            , (intmax_t)s
            , ms
            );
}

long int get_current_time_ms_part (void) {
    long            milliseconds;
    time_t          seconds;
    struct timespec spec;

    clock_gettime(CLOCK_REALTIME, &spec);

    seconds  = spec.tv_sec;
    milliseconds = round(spec.tv_nsec / 1.0e6); // Convert nanoseconds to milliseconds
    return spec.tv_nsec;
}

int main(int argc, char **argv) {
    /**
     * time precision is 1 second. 2+ calls in same second return same value
     */
    //srand(time(NULL));
    srand(get_current_time_ms_part());

    int random_value = rand_lim(1);

    //printf("value: %d\n", random_value);
    printf("%d", random_value);

    //return rand_lim(1);
    return random_value;
};