1 use 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)]
atanhf(mut x: f32) -> f329 pub 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 {
33         -x
34     } else {
35         x
36     }
37 }
38