bitfields.rs

#![feature(macro_rules)]
#![feature(globs)]
use std::fmt::*;

macro_rules! bitfield(
    { $name:ident: $repr:ty,
      $(($getter:ident, $setter:ident): $width:expr),+ } => (
        #[packed]
        #[deriving(Show)]
        struct $name($repr);
        impl $name {
            fn repr(&self) -> $repr {
                match *self {
                    $name(r) => r
                }
            }
            
            fn repr_mut<'a>(&'a mut self) -> &'a mut $repr {
                match *self {
                    $name(ref mut r) => r
                }
            }
        }
        bitfield_fields!($name, $repr, 0, $(($getter, $setter): $width,)*)
    );
)

macro_rules! bitfield_fields(
    ($name:ident, $repr:ty, $offset:expr) => {};
    ($name:ident, $repr:ty, $offset:expr,) => {};
    ($name:ident, $repr:ty, $offset:expr, ($getter:ident, $setter:ident): $width:expr $($args:tt)*) => {
        impl $name {
            fn $getter(&self) -> $repr {
                (self.repr() >> ($offset)) & ((1 << $width) - 1)
            }
            
            fn $setter(&mut self, val: $repr) {
                *self.repr_mut() &= !(((1 << $width) - 1) << $offset);
                *self.repr_mut() |= val << ($offset);
            }
        }
        bitfield_fields!($name, $repr, $offset + $width $($args)*)
    }
)

bitfield! { MyBitField: u16,
    (get_a, set_a): 2,
    (get_b, set_b): 5
}

fn main() {
    let mut bits = MyBitField(0);
    bits.set_a(0b11);
    bits.set_b(0b11011);
    println!("{:t}", bits.repr());
}