libm/math/
acoshf.rs

1use super::{log1pf, logf, sqrtf};
2
3const LN2: f32 = 0.693147180559945309417232121458176568;
4
5/// Inverse hyperbolic cosine (f32)
6///
7/// Calculates the inverse hyperbolic cosine of `x`.
8/// Is defined as `log(x + sqrt(x*x-1))`.
9/// `x` must be a number greater than or equal to 1.
10#[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
11pub fn acoshf(x: f32) -> f32 {
12    let u = x.to_bits();
13    let a = u & 0x7fffffff;
14
15    if a < 0x3f800000 + (1 << 23) {
16        /* |x| < 2, invalid if x < 1 or nan */
17        /* up to 2ulp error in [1,1.125] */
18        return log1pf(x - 1.0 + sqrtf((x - 1.0) * (x - 1.0) + 2.0 * (x - 1.0)));
19    }
20    if a < 0x3f800000 + (12 << 23) {
21        /* |x| < 0x1p12 */
22        return logf(2.0 * x - 1.0 / (x + sqrtf(x * x - 1.0)));
23    }
24    /* x >= 0x1p12 */
25    return logf(x) + LN2;
26}