1use super::log1pf;
2
3/* atanh(x) = log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2 ~= x + x^3/3 + o(x^5) */
4/// Inverse hyperbolic tangent (f32)
5///
6/// Calculates the inverse hyperbolic tangent of `x`.
7/// Is defined as `log((1+x)/(1-x))/2 = log1p(2x/(1-x))/2`.
8#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
9pub fn atanhf(mut x: f32) -> f32 {
10 let mut u = x.to_bits();
11 let sign = (u >> 31) != 0;
12
13 /* |x| */
14 u &= 0x7fffffff;
15 x = f32::from_bits(u);
16
17 if u < 0x3f800000 - (1 << 23) {
18 if u < 0x3f800000 - (32 << 23) {
19 /* handle underflow */
20 if u < (1 << 23) {
21 force_eval!((x * x) as f32);
22 }
23 } else {
24 /* |x| < 0.5, up to 1.7ulp error */
25 x = 0.5 * log1pf(2.0 * x + 2.0 * x * x / (1.0 - x));
26 }
27 } else {
28 /* avoid overflow */
29 x = 0.5 * log1pf(2.0 * (x / (1.0 - x)));
30 }
31
32 if sign { -x } else { x }
33}
34