register.rs

#![feature(unsafe_destructor)]

use std::ty::Unsafe;
use std::kinds::marker::InvariantType;

/// This represents a register
struct RegValue<Packed, Unpacked> {
  value: Unsafe<Packed>,
}

/// This represents the value of a particular register named AReg1 and
/// can be used to manipulate the fields of this register atomically
struct AReg1<'a> {
  value: u32,
  mask: u32,
  // this may need to turn into a raw pointer due to unsafe destructors
  reg: *mut u32,
}

impl<'a> AReg1<'a> {
  /// bit 0
  pub fn set_field1<'b>(&'b mut self, value: bool) -> &'b mut AReg1<'a> {
    self.value = (!(1<<0) & self.value) | ((value as u32 & 1) << 0);
    self.mask = self.mask | 1;
    self
  }

  /// bits 1..4
  pub fn set_field2<'b>(&'b mut self, value: u32) -> &'b mut AReg1<'a> {
    self.value = (!(7<<1) & self.value) | ((value as u32 & 0x7) << 1);
    self.mask = self.mask | (7<<1);
    self
  }
}

/*
impl<'b> Deref<AReg1<'b>> for RegValue<u32, AReg1<'b>> {
  fn deref<'a>(&'a self) -> &'a AReg1<'a> {
    &AReg1 {value: *self.value.get(), mask: 0, reg: self}
  }
}
*/

impl<'a> RegValue<u32, AReg1<'a>> {
  pub fn get_field1(&mut self) -> bool {
    unsafe {
      (*self.value.get() >> 0) & 1 != 0
    }
  }

  pub fn set_field1(&mut self, val: bool) -> AReg1<'a> {
    let val = if val { 1 } else { 0 };
    unsafe {
      AReg1 {value: val, mask: 1<<0, reg: self.value.get()}
    }
  }
  pub fn get_field2(&mut self) -> u32 {
    unsafe {
      (*self.value.get() >> 1) & 7
    }
  }

  pub fn set_field2(&mut self, val: u32) -> AReg1<'a> {
    let val = (val & 7) << 1;
    unsafe {
      AReg1 {value: val, mask: 7<<1, reg: self.value.get()}
    }
  }
}

#[unsafe_destructor]
impl<'a> Drop for AReg1<'a> {
  fn drop(&mut self) {
    unsafe {
      *self.reg = self.value | (*self.reg & !self.mask);
    }
  }
}

static mut areg1: RegValue<u32, AReg1<'static>> =
  RegValue { value: Unsafe {value: 0,
                            marker1: InvariantType }};

fn main() {
  unsafe {
    areg1
      .set_field1(true)
      .set_field2(5);
    println!("field1 = {}", areg1.get_field1());
    println!("field2 = {}", areg1.get_field2());
  }
}