lighthouse-pulse/lighthouse/shuffling/mod.rs

extern crate blake2_rfc;

mod rng;

use self::rng::ShuffleRng;

#[derive(Debug)]
pub enum ShuffleErr {
    ExceedsListLength,
}

/// Performs a deterministic, in-place shuffle of a vector of bytes. 
/// The final order of the shuffle is determined by successive hashes
/// of the supplied `seed`.
pub fn shuffle(
    seed: &[u8],
    mut list: Vec<usize>) 
    -> Result<Vec<usize>, ShuffleErr>
{
    let mut rng = ShuffleRng::new(seed);
    if list.len() > rng.rand_max as usize {
        return Err(ShuffleErr::ExceedsListLength);
    } 
    for i in 0..(list.len() - 1) {
        let n = list.len() - i;
        let j = rng.rand_range(n as u32) as usize + i;
        list.swap(i, j);
    }
    Ok(list)
}


#[cfg(test)]
mod tests {
    use super::*;
    use super::blake2_rfc::blake2s::{ blake2s, Blake2sResult };

    fn hash(seed: &[u8]) -> Blake2sResult {
        blake2s(32, &[], seed)
    }

    #[test]
    fn test_shuffling() {
        let seed = hash(b"4kn4driuctg8");
        let list: Vec<usize> = (0..12).collect();
        let s = shuffle(seed.as_bytes(), list).unwrap();
        assert_eq!(
            s,
            vec![7, 4, 8, 6, 5, 3, 0, 11, 1, 2, 10, 9],
        )
    }
}