Macro unsigned_ones_complement_impl 

macro_rules! unsigned_ones_complement_impl {
    ($SelfT:ty, $BITS:expr_2021, $InnerT:ty, $SignedPeerT:ty) => { ... };
}

This macro implements the base functionality of the unsigned types. The SelfT argument is the name of the (unsigned in this case) type we are defining. BITS is the bit width of the type we are defining. InnerT is the name of the native type which will store those bits. SignedPeerT is the name of the equivalent signed type having the same width (e.g. for Unsigned18Bit this should be Signed18Bit).