docs: public static double cdf(double val, double dof) {
      double v = val * val * .5;
      // regularizedGammaP will return NaN for infinite values!
      return val < 0. ? 0. : v < Double.POSITIVE_INFINITY ? GammaDistribution.regularizedGammaP(dof * .5, v) : v == v ? 1. : Double.NaN;
    }