Function bitncmp 

pub fn bitncmp(l: &[u8; 16], r: &[u8; 16], n: u8) -> i32

bitncmp: the order of the first n bits of two addresses. PostgreSQL compares the whole bytes with memcmp, which gives the difference of the first bytes that differ on the reference server, and then the bits of the last byte, which give 1 or -1.