1 use super::expm1; 2 3 /* tanh(x) = (exp(x) - exp(-x))/(exp(x) + exp(-x)) 4 * = (exp(2*x) - 1)/(exp(2*x) - 1 + 2) 5 * = (1 - exp(-2*x))/(exp(-2*x) - 1 + 2) 6 */ 7 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] tanh(mut x: f64) -> f648pub fn tanh(mut x: f64) -> f64 { 9 let mut uf: f64 = x; 10 let mut ui: u64 = f64::to_bits(uf); 11 12 let w: u32; 13 let sign: bool; 14 let mut t: f64; 15 16 /* x = |x| */ 17 sign = ui >> 63 != 0; 18 ui &= !1 / 2; 19 uf = f64::from_bits(ui); 20 x = uf; 21 w = (ui >> 32) as u32; 22 23 if w > 0x3fe193ea { 24 /* |x| > log(3)/2 ~= 0.5493 or nan */ 25 if w > 0x40340000 { 26 /* |x| > 20 or nan */ 27 /* note: this branch avoids raising overflow */ 28 t = 1.0 - 0.0 / x; 29 } else { 30 t = expm1(2.0 * x); 31 t = 1.0 - 2.0 / (t + 2.0); 32 } 33 } else if w > 0x3fd058ae { 34 /* |x| > log(5/3)/2 ~= 0.2554 */ 35 t = expm1(2.0 * x); 36 t = t / (t + 2.0); 37 } else if w >= 0x00100000 { 38 /* |x| >= 0x1p-1022, up to 2ulp error in [0.1,0.2554] */ 39 t = expm1(-2.0 * x); 40 t = -t / (t + 2.0); 41 } else { 42 /* |x| is subnormal */ 43 /* note: the branch above would not raise underflow in [0x1p-1023,0x1p-1022) */ 44 force_eval!(x as f32); 45 t = x; 46 } 47 48 if sign { 49 -t 50 } else { 51 t 52 } 53 } 54