Attempted implementation of generating a unit vector from a given offset.

unit vector

double *randomVector(double v[2], int x, int y){
    /* generates two coordinates on a unit circle which are used
     * for the 4 vectors from each grid point.
     */
    srand(time(NULL));
    double r;
    int cont = 1;
    /* http://burtleburtle.net/bob/rand/unitvec.html */
    do {
        double m = (double)rand()/(double)(RAND_MAX-1);
        double n = (double)rand()/(double)(RAND_MAX-1);
        v[0] = 2*m-1;
        v[1] = 2*n-1;
        r = (v[0]*v[0])+(v[1]*v[1]);
    } while (r > 1.0 || r == 0);
    double l = sqrt(-2*log(r)/r);
    // v[0]: x, v[1]: y
    v[0] = v[0]*l+x;
    v[1] = v[1]*l+y;
    printf("v0: %f, v1: %f\n", v[0], v[1]);
    return v;
}