s = 1.0 / x * (scale ? 1.0 : Math.exp(-x))
            result_c = ChebyshevSeries.eval((40.0 / x + 7.0) / 3.0, :ae12, with_error)
            result_c, result_c_err = result_c if with_error
            result   = s * (1.0 + result_c)
            error ||= (s * result_c_err) + 2.0 * Float::EPSILON * result.abs