Macro impl_discrete_steps_integer 

macro_rules! impl_discrete_steps_integer {
    (@common $u_source:ident) => { ... };
    ($u_source:ident $i_source:ident; $($u_narrower:ident $i_narrower:ident),*; $($u_wider:ident $i_wider:ident),*) => { ... };
}