Function fast_log2f 

pub unsafe extern "C" fn fast_log2f(x: f32) -> f32

Calculate the fast approximate base 2 logarithm of the input argument x.

Nvidia docs

Returns

Returns an approximation to . For accuracy information for this function see the CUDA C Programming Guide, Appendix D.2, Table 9. Input and output in the denormal range is flushed to sign preserving 0.0.