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module math
const (
tanh_p = [
-9.64399179425052238628e-1,
-9.92877231001918586564e+1,
-1.61468768441708447952e+3,
]
tanh_q = [
1.12811678491632931402e+2,
2.23548839060100448583e+3,
4.84406305325125486048e+3,
]
)
// tanh returns the hyperbolic tangent of x.
//
// special cases are:
// tanh(±0) = ±0
// tanh(±inf) = ±1
// tanh(nan) = nan
pub fn tanh(x f64) f64 {
maxlog := 8.8029691931113054295988e+01 // log(2**127)
mut z := abs(x)
if z > 0.5 * maxlog {
if x < 0 {
return f64(-1)
}
return 1.0
} else if z >= 0.625 {
s := exp(2.0 * z)
z = 1.0 - 2.0 / (s + 1.0)
if x < 0 {
z = -z
}
} else {
if x == 0 {
return x
}
s := x * x
z = x + x * s * ((math.tanh_p[0] * s + math.tanh_p[1]) * s + math.tanh_p[2]) / (((s +
math.tanh_q[0]) * s + math.tanh_q[1]) * s + math.tanh_q[2])
}
return z
}
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