thread safe, but non-portable randamize function.

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

//
// returns random number from zero to max.
// to compile this, run the following command.
// $ gcc -Wall -lm -lrt filename
//
double getRand(struct drand48_data *data, int max)
{
    double rand = 0;
    drand48_r(data, &rand);
    rand = floor(rand * max);
    return rand;
}

int initRand(struct drand48_data *data)
{
    struct timespec time;
    int result = clock_gettime(CLOCK_REALTIME, &time);
    if (result == -1) {
        perror("clock_gettime");
        return -1;
    }

    srand48_r(time.tv_nsec, data);
    return 0;
}

int main(int argc, char *argv[])
{
    int c, result;
    struct drand48_data data;
    result = initRand(&data);
    if (result == -1) {
        return result;
    }
    for (c = 0; c < 100; c++) {
        printf("%.0f\n", getRand(&data, 500)); 
    }
    return 0;
}