lighthouse/eth2/utils/cached_tree_hash/src/impls/vec.rs

use super::*;
use crate::merkleize::{merkleize, num_sanitized_leaves, sanitise_bytes};

impl<T> CachedTreeHash<Vec<T>> for Vec<T>
where
    T: CachedTreeHash<T> + TreeHash,
{
    fn new_tree_hash_cache(&self, depth: usize) -> Result<TreeHashCache, Error> {
        let overlay = self.tree_hash_cache_overlay(0, depth)?;

        let mut cache = match T::tree_hash_type() {
            TreeHashType::Basic => TreeHashCache::from_bytes(
                merkleize(get_packed_leaves(self)?),
                false,
                Some(overlay.clone()),
            ),
            TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
                let subtrees = self
                    .iter()
                    .map(|item| TreeHashCache::new(item, depth + 1))
                    .collect::<Result<Vec<TreeHashCache>, _>>()?;

                TreeHashCache::from_leaves_and_subtrees(self, subtrees, depth)
            }
        }?;

        cache.add_length_nodes(overlay.chunk_range(), self.len())?;

        Ok(cache)
    }

    fn num_tree_hash_cache_chunks(&self) -> usize {
        BTreeOverlay::new(self, 0, 0)
            .and_then(|o| Ok(o.num_chunks()))
            .unwrap_or_else(|_| 1)
            + 2
    }

    fn tree_hash_cache_overlay(
        &self,
        chunk_offset: usize,
        depth: usize,
    ) -> Result<BTreeOverlay, Error> {
        let lengths = match T::tree_hash_type() {
            TreeHashType::Basic => {
                // Ceil division.
                let num_leaves = (self.len() + T::tree_hash_packing_factor() - 1)
                    / T::tree_hash_packing_factor();

                // Disallow zero-length as an empty list still has one all-padding node.
                vec![1; std::cmp::max(1, num_leaves)]
            }
            TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
                let mut lengths = vec![];

                for item in self {
                    lengths.push(item.num_tree_hash_cache_chunks())
                }

                // Disallow zero-length as an empty list still has one all-padding node.
                if lengths.is_empty() {
                    lengths.push(1);
                }

                lengths
            }
        };

        BTreeOverlay::from_lengths(chunk_offset, self.len(), depth, lengths)
    }

    fn update_tree_hash_cache(&self, cache: &mut TreeHashCache) -> Result<(), Error> {
        // Skip the length-mixed-in root node.
        cache.chunk_index += 1;

        let old_overlay = cache.get_overlay(cache.overlay_index, cache.chunk_index)?;
        let new_overlay = BTreeOverlay::new(self, cache.chunk_index, old_overlay.depth)?;

        cache.replace_overlay(cache.overlay_index, cache.chunk_index, new_overlay.clone())?;

        cache.overlay_index += 1;

        match T::tree_hash_type() {
            TreeHashType::Basic => {
                let mut buf = vec![0; HASHSIZE];
                let item_bytes = HASHSIZE / T::tree_hash_packing_factor();

                // Iterate through each of the leaf nodes.
                for i in 0..new_overlay.num_leaf_nodes() {
                    // Iterate through the number of items that may be packing into the leaf node.
                    for j in 0..T::tree_hash_packing_factor() {
                        // Create a mut slice that can be filled with either a serialized item or
                        // padding.
                        let buf_slice = &mut buf[j * item_bytes..(j + 1) * item_bytes];

                        // Attempt to get the item for this portion of the chunk. If it exists,
                        // update `buf` with it's serialized bytes. If it doesn't exist, update
                        // `buf` with padding.
                        match self.get(i * T::tree_hash_packing_factor() + j) {
                            Some(item) => {
                                buf_slice.copy_from_slice(&item.tree_hash_packed_encoding());
                            }
                            None => buf_slice.copy_from_slice(&vec![0; item_bytes]),
                        }
                    }

                    // Update the chunk if the generated `buf` is not the same as the cache.
                    let chunk = new_overlay.first_leaf_node() + i;
                    cache.maybe_update_chunk(chunk, &buf)?;
                }
            }
            TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
                for i in 0..new_overlay.num_leaf_nodes() {
                    // Adjust `i` so it is a leaf node for each of the overlays.
                    let old_i = i + old_overlay.num_internal_nodes();
                    let new_i = i + new_overlay.num_internal_nodes();

                    match (
                        old_overlay.get_leaf_node(old_i)?,
                        new_overlay.get_leaf_node(new_i)?,
                    ) {
                        // The item existed in the previous list and exists in the current list.
                        (Some(_old), Some(new)) => {
                            cache.chunk_index = new.start;

                            self[i].update_tree_hash_cache(cache)?;
                        }
                        // The item did not exist in the previous list but does exist in this list.
                        //
                        // Viz., the list has been lengthened.
                        (None, Some(new)) => {
                            let (bytes, mut bools, overlays) =
                                TreeHashCache::new(&self[i], new_overlay.depth + 1)?
                                    .into_components();

                            // Record the number of overlays, this will be used later in the fn.
                            let num_overlays = overlays.len();

                            // Flag the root node of the new tree as dirty.
                            bools[0] = true;

                            cache.splice(new.start..new.start + 1, bytes, bools);
                            cache
                                .overlays
                                .splice(cache.overlay_index..cache.overlay_index, overlays);

                            cache.overlay_index += num_overlays;
                        }
                        // The item existed in the previous list but does not exist in this list.
                        //
                        // Viz., the list has been shortened.
                        (Some(old), None) => {
                            if new_overlay.num_items == 0 {
                                // In this case, the list has been made empty and we should make
                                // this node padding.
                                cache.maybe_update_chunk(new_overlay.root(), &[0; HASHSIZE])?;
                            } else {
                                // In this case, there are some items in the new list and we should
                                // splice out the entire tree of the removed node, replacing it
                                // with a single padding node.
                                cache.splice(old, vec![0; HASHSIZE], vec![true]);
                            }
                        }
                        // The item didn't exist in the old list and doesn't exist in the new list,
                        // nothing to do.
                        (None, None) => {}
                    }
                }

                // Clean out any excess overlays that may or may not be remaining if the list was
                // shortened.
                cache.remove_proceeding_child_overlays(cache.overlay_index, new_overlay.depth);
            }
        }

        cache.update_internal_nodes(&new_overlay)?;

        // Mix in length
        cache.mix_in_length(new_overlay.chunk_range(), self.len())?;

        // Skip an extra node to clear the length node.
        cache.chunk_index = new_overlay.next_node() + 1;

        Ok(())
    }
}

fn get_packed_leaves<T>(vec: &Vec<T>) -> Result<Vec<u8>, Error>
where
    T: CachedTreeHash<T>,
{
    let num_packed_bytes = (BYTES_PER_CHUNK / T::tree_hash_packing_factor()) * vec.len();
    let num_leaves = num_sanitized_leaves(num_packed_bytes);

    let mut packed = Vec::with_capacity(num_leaves * HASHSIZE);

    for item in vec {
        packed.append(&mut item.tree_hash_packed_encoding());
    }

    Ok(sanitise_bytes(packed))
}