module math

// sinh calculates hyperbolic sine.
pub fn sinh(x_ f64) f64 {
    mut x := x_
    // The coefficients are #2029 from Hart & Cheney. (20.36D)
    p0 := -0.6307673640497716991184787251e+6
    p1 := -0.8991272022039509355398013511e+5
    p2 := -0.2894211355989563807284660366e+4
    p3 := -0.2630563213397497062819489e+2
    q0 := -0.6307673640497716991212077277e+6
    q1 := 0.1521517378790019070696485176e+5
    q2 := -0.173678953558233699533450911e+3
    mut neg := false
    if x < 0 {
        x = -x
        neg = true
    }
    mut temp := 0.0
    if x > 21 {
        temp = exp(x) * 0.5
    } else if x > 0.5 {
        ex := exp(x)
        temp = (ex - 1.0 / ex) * 0.5
    } else {
        sq := x * x
        temp = (((p3 * sq + p2) * sq + p1) * sq + p0) * x
        temp = temp / (((sq + q2) * sq + q1) * sq + q0)
    }
    if neg {
        temp = -temp
    }
    return temp
}

// cosh returns the hyperbolic cosine of x in radians
//
// special cases are:
// cosh(±0) = 1
// cosh(±inf) = +inf
// cosh(nan) = nan
pub fn cosh(x f64) f64 {
    abs_x := abs(x)
    if abs_x > 21 {
        return exp(abs_x) * 0.5
    }
    ex := exp(abs_x)
    return (ex + 1.0 / ex) * 0.5
}