bitfield.rs

use vec;

pub trait BitField {
    fn get(&self, index: u8) -> bool;
    fn set(&mut self, index: u8, value: bool);
    fn ensure_size(&mut self, byte: u8);
}

pub struct U8BitField {
    u8s: ~[u8],
    alloc: u8
}

impl BitField for U8BitField {
    fn set(&mut self, index: u8, value: bool) {
        let bit = index % 8;
        let idx = index - (bit * 8);
        self.ensure_size(idx + 1);
        
        let byte = self.u8s[idx];
        
        if (value) {
            self.u8s[idx] = byte | (1 << bit)
        } else {
            self.u8s[idx] = byte & !((1 << bit) as u8)
        }
    }
    
    fn get(&self, index: u8) -> bool {
        let bit = index % 8;
        let idx = index - (bit * 8);
        
        if (self.alloc < idx + 1) {
            return false
        }
        
        let byte = self.u8s[idx];
        (byte & (1 << bit)) > 0
    }
    
    fn ensure_size(&mut self, byte: u8) {
        unsafe {
            while (self.alloc < byte) {
                self.u8s.push_fast(0);
                self.alloc += 1
            }
        }
    }
}