Function expm1 

pub fn expm1(x: f64) -> f64

e^x - 1, accurate for small x (no catastrophic cancellation).

use mathverse_core::float::expm1;
assert!((expm1(1e-10) - 1e-10).abs() < 1e-20);
assert!((expm1(1.0) - (core::f64::consts::E - 1.0)).abs() < 1e-15);