Kademlia DHT finding bucket index for a node

Question

I am trying to implement a Kademlia distributed hash table in rust and I am wondering if there is a mistake with the way im implementing find_node_bucket_index in the routing table. Correct me if im wrong, but the way that I understood how nodes are placed in the routing table is:

1. you get the distance of the two nodes using the xor metric (distance function below).
2. then do the xor for the distance found and the node id using the same distance function.
3. Then, you find the prefix length of the matching bits between the node Id and the distance using the result of step 2.

Hopefully that made sense, if not, here is the code:

distance function:

    fn distance_from(&self, b: &Self) -> [u8; GUID_LEN] {
        let mut res = [0; GUID_LEN];
        for (i, val) in self.0.iter().enumerate() {
            res[i] = val ^ b.0[i]
        }

        res
    }

find bucket index function:

    pub fn find_index(id: &GUID, node_id: &GUID) -> usize {
        let dist = node_id.distance_from(id);
        let diff = dist.distance_from(&node_id.0);

        for i in 0..GUID_LEN {
            for j in (0..8).rev() {
                let bit = diff[i] & (1 << j);
                if bit != 0 {
                    return 8 * i + j;
                }
            }
        }

        GUID_LEN * 8 - 1
    }