| use super::{log, log1p, sqrt}; |
| |
| const LN2: f64 = 0.693147180559945309417232121458176568; /* 0x3fe62e42, 0xfefa39ef*/ |
| |
| /// Inverse hyperbolic cosine (f64) |
| /// |
| /// Calculates the inverse hyperbolic cosine of `x`. |
| /// Is defined as `log(x + sqrt(x*x-1))`. |
| /// `x` must be a number greater than or equal to 1. |
| pub fn acosh(x: f64) -> f64 { |
| let u = x.to_bits(); |
| let e = ((u >> 52) as usize) & 0x7ff; |
| |
| /* x < 1 domain error is handled in the called functions */ |
| |
| if e < 0x3ff + 1 { |
| /* |x| < 2, up to 2ulp error in [1,1.125] */ |
| return log1p(x - 1.0 + sqrt((x - 1.0) * (x - 1.0) + 2.0 * (x - 1.0))); |
| } |
| if e < 0x3ff + 26 { |
| /* |x| < 0x1p26 */ |
| return log(2.0 * x - 1.0 / (x + sqrt(x * x - 1.0))); |
| } |
| /* |x| >= 0x1p26 or nan */ |
| return log(x) + LN2; |
| } |
