Function signf 

pub fn signf(x: f64) -> f64

Returns -1.0 if x is negative, 1.0 if x is positive, and 0.0 if x is zero. For nan values of x it returns 0.0.

signf(-6.5) # Returns -1.0
signf(0.0)  # Returns 0.0
signf(6.5)  # Returns 1.0
signf(NAN)  # Returns 0.0