fn main() {
    let mut result = [0x00; HASH_SIZE];
    for (hash_items, res) in password_hash.chunks(2).zip(result.iter_mut()) {
        let hn = magic_transform(*hash_items.first().unwrap());
        let ln = magic_transform(*hash_items.last().unwrap());
        *res = (hn << 4) | ln;
    }

    // isn't it the same as

    let result = password_hash
        .map(|elem| {
            if elem > b'9' {
                elem + 10 - b'A'
            } else {
                elem.wrapping_sub(b'0')
            }
        })
        .chunks(2)
        .map(|pair| (pair[0] << 4) | pair[1])
        .collect();

    // ?
}