function erfc3(y) {
    var ysq = 1 / (y * y);
    var xnum = P[2][5] * ysq;
    var xden = ysq;
    var i;

    for (i = 0; i < 4; i += 1) {
      xnum = (xnum + P[2][i]) * ysq;
      xden = (xden + Q[2][i]) * ysq;
    }

    var result = ysq * (xnum + P[2][4]) / (xden + Q[2][4]);
    result = (SQRPI - result) / y;
    ysq = parseInt(y * 16) / 16;
    var del = (y - ysq) * (y + ysq);
    return Math.exp(-ysq * ysq) * Math.exp(-del) * result;
  }
Approximates the complement of the error function erfc() for x > 4.0 using
this function:

erfc(x) = (e^(-x^2) / x) * [ 1/sqrt(pi) +
              n
   1/(x^2) * sum (p_j * x^(-2j)) / (q_j * x^(-2j)) ]
             j=0