code: public static double logcdf(double val, double loc, double scale, double shape) {
      val = (val - loc) / scale;
      return FastMath.log1p(FastMath.exp(-val)) * -shape;
    }
docs: log Cumulative density function.
  
  TODO: untested.
  
  @param val Value
  @param loc Location
  @param scale Scale
  @param shape Shape
  @return log PDF