static int iGetRoots(double abc[], double xx[])
    // Returns real roots of a quadratic form
    // M.Lampton UCB SSL 2003, 2011
    {
        double a = abc[0]; 
        double b = abc[1]; 
        double c = abc[2]; 
        xx[0] = xx[1] = -0.0; 

        if (a == 0.0)
        {
            if (b == 0.0)
              return 0; 
            xx[0] = xx[1] = -c/b; 
            return 1; 
        }
        if (c == 0.0)
        {
            xx[0] = 0.0; 
            xx[1] = -b/a; 
            return 2;
        }
        if (b == 0.0)
        {
            if (c/a > 0.0)
              return 0;
            xx[0]= Math.sqrt(-c/a); 
            xx[1] = -xx[0];  
            return 2;
        }

        //-------abc all nonzero-----

        double discrim = b*b-4.0*a*c; 
        if (discrim < 0.0)
          return 0; 
        if (discrim == 0.0)
        {
            xx[0] = xx[1] = -b/(2*a); 
            return 2; 
        }
        double root = Math.sqrt(discrim); 
        double q = (b>0.0) ? (b+root)/2 : (b-root)/2; 
        xx[0] = -c/q; 
        xx[1] = -q/a; 
        return 2;       
    }