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use super::expm1;
/* 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)
*/
#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
pub fn tanh(mut x: f64) -> f64 {
let mut uf: f64 = x;
let mut ui: u64 = f64::to_bits(uf);
let w: u32;
let sign: bool;
let mut t: f64;
/* x = |x| */
sign = ui >> 63 != 0;
ui &= !1 / 2;
uf = f64::from_bits(ui);
x = uf;
w = (ui >> 32) as u32;
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;
}
if sign {
-t
} else {
t
}
}