| use super::{log1pf, logf, sqrtf}; |
| |
| const LN2: f32 = 0.693147180559945309417232121458176568; |
| |
| /// Inverse hyperbolic cosine (f32) |
| /// |
| /// 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. |
| #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)] |
| pub fn acoshf(x: f32) -> f32 { |
| let u = x.to_bits(); |
| let a = u & 0x7fffffff; |
| |
| if a < 0x3f800000 + (1 << 23) { |
| /* |x| < 2, invalid if x < 1 or nan */ |
| /* up to 2ulp error in [1,1.125] */ |
| return log1pf(x - 1.0 + sqrtf((x - 1.0) * (x - 1.0) + 2.0 * (x - 1.0))); |
| } |
| if a < 0x3f800000 + (12 << 23) { |
| /* |x| < 0x1p12 */ |
| return logf(2.0 * x - 1.0 / (x + sqrtf(x * x - 1.0))); |
| } |
| /* x >= 0x1p12 */ |
| return logf(x) + LN2; |
| } |
