Mersenne Twister 19937 PRNG

mersenne_twister.rs

fn initialize_generator(mt: &mut [uint], index: &mut uint, seed: uint)
{
    mt[0] = seed;
    *index = 0;

    for i in range(1, 624) {
        mt[i] = (
            (
                1812433253 * (mt[i-1] ^ (mt[i-1] >> 30))
            ) + i
        ) % (1 << 32);
    }
}


fn extract_number(mt: &mut [uint], index: &mut uint) -> uint
{
    if *index == 0 {
        generate_numbers(mt);
    }

    let mut y = mt[*index];
    y = y ^ (y >> 11);
    y = y ^ ((y << 7) & 2636928640);
    y = y ^ ((y << 15) & 4022730752);
    y = y ^ (y >> 18);
    
    *index = (*index + 1) % 624;

    y
}


fn generate_numbers(mt: &mut [uint])
{
    for i in range(0u, 623u) {
        let y = (mt[i] & 0x80000000) + (mt[(i+1) % 624] & 0x7fffffff);

        mt[i] = mt[(i+397) % 624] ^ (y >> 1);

        if y % 2 != 0 {
            mt[i] ^= 2567483615
        }
    }
}


fn main() {
    let mut mt = [0u, .. 624];
    let mut index = 0u;
    let my_seed = 10u;

    initialize_generator(&mut mt, &mut index, my_seed);

    for i in range(0u, 10u) {
        let n = extract_number(&mut mt, &mut index);
        println!("@ {} {}", i, n);
    }
}