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111: Implement tanh r=japaric a=porglezomp Closes #37 Co-authored-by: C Jones <code@calebjones.net>
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,52 @@ | ||
use super::expm1; | ||
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/* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x)) | ||
* = (exp(2*x) - 1)/(exp(2*x) - 1 + 2) | ||
* = (1 - exp(-2*x))/(exp(-2*x) - 1 + 2) | ||
*/ | ||
pub fn tanh(mut x: f64) -> f64 { | ||
let mut uf: f64 = x; | ||
let mut ui: u64 = f64::to_bits(uf); | ||
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let w: u32; | ||
let sign: bool; | ||
let mut t: f64; | ||
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/* x = |x| */ | ||
sign = ui >> 63 != 0; | ||
ui &= !1 / 2; | ||
uf = f64::from_bits(ui); | ||
x = uf; | ||
w = (ui >> 32) as u32; | ||
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if w > 0x3fe193ea { | ||
/* |x| > log(3)/2 ~= 0.5493 or nan */ | ||
if w > 0x40340000 { | ||
/* |x| > 20 or nan */ | ||
/* note: this branch avoids raising overflow */ | ||
t = 1.0 - 0.0 / x; | ||
} else { | ||
t = expm1(2.0 * x); | ||
t = 1.0 - 2.0 / (t + 2.0); | ||
} | ||
} else if w > 0x3fd058ae { | ||
/* |x| > log(5/3)/2 ~= 0.2554 */ | ||
t = expm1(2.0 * x); | ||
t = t / (t + 2.0); | ||
} else if w >= 0x00100000 { | ||
/* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */ | ||
t = expm1(-2.0 * x); | ||
t = -t / (t + 2.0); | ||
} else { | ||
/* |x| is subnormal */ | ||
/* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */ | ||
force_eval!(x as f32); | ||
t = x; | ||
} | ||
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if sign { | ||
-t | ||
} else { | ||
t | ||
} | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -717,7 +717,7 @@ f64_f64! { | |
sinh, | ||
sqrt, | ||
tan, | ||
// tanh, | ||
tanh, | ||
trunc, | ||
fabs, | ||
} | ||
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