* @return inverse hyperbolic sine of a
     */
    public static double asinh(double a) {
        boolean negative = false;
        if (a < 0) {
            negative = true;
            a = -a;
        }

        double absAsinh;
        if (a > 0.167) {
            absAsinh = FastMath.log(FastMath.sqrt(a * a + 1) + a);
        } else {
            final double a2 = a * a;
            if (a > 0.097) {
                absAsinh = a * (1 - a2 * (F_1_3 - a2 * (F_1_5 - a2 * (F_1_7 - a2 * (F_1_9 - a2 * (F_1_11 - a2 * (F_1_13 - a2 * (F_1_15 - a2 * F_1_17 * F_15_16) * F_13_14) * F_11_12) * F_9_10) * F_7_8) * F_5_6) * F_3_4) * F_1_2);
            } else if (a > 0.036) {
                absAsinh = a * (1 - a2 * (F_1_3 - a2 * (F_1_5 - a2 * (F_1_7 - a2 * (F_1_9 - a2 * (F_1_11 - a2 * F_1_13 * F_11_12) * F_9_10) * F_7_8) * F_5_6) * F_3_4) * F_1_2);
            } else if (a > 0.0036) {
                absAsinh = a * (1 - a2 * (F_1_3 - a2 * (F_1_5 - a2 * (F_1_7 - a2 * F_1_9 * F_7_8) * F_5_6) * F_3_4) * F_1_2);
            } else {
                absAsinh = a * (1 - a2 * (F_1_3 - a2 * F_1_5 * F_3_4) * F_1_2);
            }
        }

        return negative ? -absAsinh : absAsinh;
    }