Function cbrt 

pub fn cbrt(x: f64) -> f64

Cube root, fdlibm’s cbrt.

A first estimate from the high word divided by 3 (5 bits), a rational correction (23 bits), the estimate chopped to 20 bits and nudged up, then one Newton step. cbrt(±0), cbrt(±inf) and cbrt(NaN) return the argument.