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