Implement CachedTreeHash for TreeHashVector

eth2/types/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2018"
 [dependencies]
 bls = { path = "../utils/bls" }
 boolean-bitfield = { path = "../utils/boolean-bitfield" }
+cached_tree_hash = { path = "../utils/cached_tree_hash" }
 dirs = "1.0"
 derivative = "1.0"
 ethereum-types = "0.5"

eth2/types/src/tree_hash_vector.rs

@@ -1,4 +1,5 @@
 use crate::test_utils::{RngCore, TestRandom};
+use cached_tree_hash::CachedTreeHash;
 use serde_derive::{Deserialize, Serialize};
 use ssz::{Decodable, DecodeError, Encodable, SszStream};
 use std::ops::{Deref, DerefMut};
@@ -54,6 +55,43 @@ where
     }
 }
 
+impl<T> CachedTreeHash<TreeHashVector<T>> for TreeHashVector<T>
+where
+    T: CachedTreeHash<T> + TreeHash,
+{
+    fn new_tree_hash_cache(
+        &self,
+        depth: usize,
+    ) -> Result<cached_tree_hash::TreeHashCache, cached_tree_hash::Error> {
+        let (cache, _overlay) = cached_tree_hash::impls::vec::new_tree_hash_cache(self, depth)?;
+
+        Ok(cache)
+    }
+
+    fn num_tree_hash_cache_chunks(&self) -> usize {
+        cached_tree_hash::BTreeOverlay::new(self, 0, 0)
+            .and_then(|o| Ok(o.num_chunks()))
+            .unwrap_or_else(|_| 1)
+    }
+
+    fn tree_hash_cache_overlay(
+        &self,
+        chunk_offset: usize,
+        depth: usize,
+    ) -> Result<cached_tree_hash::BTreeOverlay, cached_tree_hash::Error> {
+        cached_tree_hash::impls::vec::produce_overlay(self, chunk_offset, depth)
+    }
+
+    fn update_tree_hash_cache(
+        &self,
+        cache: &mut cached_tree_hash::TreeHashCache,
+    ) -> Result<(), cached_tree_hash::Error> {
+        cached_tree_hash::impls::vec::update_tree_hash_cache(self, cache)?;
+
+        Ok(())
+    }
+}
+
 impl<T> Encodable for TreeHashVector<T>
 where
     T: Encodable,

eth2/utils/cached_tree_hash/src/impls.rs

@@ -1,7 +1,7 @@
 use super::*;
 use crate::merkleize::merkleize;
 
-mod vec;
+pub mod vec;
 
 impl CachedTreeHash<u64> for u64 {
     fn new_tree_hash_cache(&self, _depth: usize) -> Result<TreeHashCache, Error> {

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

@@ -6,23 +6,7 @@ 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)
-            }
-        }?;
+        let (mut cache, overlay) = new_tree_hash_cache(self, depth)?;
 
         cache.add_length_nodes(overlay.chunk_range(), self.len())?;
 
@@ -33,7 +17,7 @@ where
         BTreeOverlay::new(self, 0, 0)
             .and_then(|o| Ok(o.num_chunks()))
             .unwrap_or_else(|_| 1)
-            + 2
+            + 2 // Add two extra nodes to cater for the length.
     }
 
     fn tree_hash_cache_overlay(
@@ -41,11 +25,61 @@ where
         chunk_offset: usize,
         depth: usize,
     ) -> Result<BTreeOverlay, Error> {
+        produce_overlay(self, chunk_offset, depth)
+    }
+
+    fn update_tree_hash_cache(&self, cache: &mut TreeHashCache) -> Result<(), Error> {
+        // Skip the length-mixed-in root node.
+        cache.chunk_index += 1;
+
+        // Update the cache, returning the new overlay.
+        let new_overlay = update_tree_hash_cache(self, cache)?;
+
+        // 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(())
+    }
+}
+
+pub fn new_tree_hash_cache<T: CachedTreeHash<T>>(
+    vec: &Vec<T>,
+    depth: usize,
+) -> Result<(TreeHashCache, BTreeOverlay), Error> {
+    let overlay = vec.tree_hash_cache_overlay(0, depth)?;
+
+    let cache = match T::tree_hash_type() {
+        TreeHashType::Basic => TreeHashCache::from_bytes(
+            merkleize(get_packed_leaves(vec)?),
+            false,
+            Some(overlay.clone()),
+        ),
+        TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
+            let subtrees = vec
+                .iter()
+                .map(|item| TreeHashCache::new(item, depth + 1))
+                .collect::<Result<Vec<TreeHashCache>, _>>()?;
+
+            TreeHashCache::from_leaves_and_subtrees(vec, subtrees, depth)
+        }
+    }?;
+
+    Ok((cache, overlay))
+}
+
+pub fn produce_overlay<T: CachedTreeHash<T>>(
+    vec: &Vec<T>,
+    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();
+            let num_leaves =
+                (vec.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)]
@@ -53,7 +87,7 @@ where
         TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
             let mut lengths = vec![];
 
-                for item in self {
+            for item in vec {
                 lengths.push(item.num_tree_hash_cache_chunks())
             }
 
@@ -66,15 +100,15 @@ where
         }
     };
 
-        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;
+    BTreeOverlay::from_lengths(chunk_offset, vec.len(), depth, lengths)
+}
 
+pub fn update_tree_hash_cache<T: CachedTreeHash<T>>(
+    vec: &Vec<T>,
+    cache: &mut TreeHashCache,
+) -> Result<BTreeOverlay, Error> {
     let old_overlay = cache.get_overlay(cache.overlay_index, cache.chunk_index)?;
-        let new_overlay = BTreeOverlay::new(self, cache.chunk_index, old_overlay.depth)?;
+    let new_overlay = BTreeOverlay::new(vec, cache.chunk_index, old_overlay.depth)?;
 
     cache.replace_overlay(cache.overlay_index, cache.chunk_index, new_overlay.clone())?;
 
@@ -96,7 +130,7 @@ where
                     // 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) {
+                    match vec.get(i * T::tree_hash_packing_factor() + j) {
                         Some(item) => {
                             buf_slice.copy_from_slice(&item.tree_hash_packed_encoding());
                         }
@@ -123,15 +157,14 @@ where
                     (Some(_old), Some(new)) => {
                         cache.chunk_index = new.start;
 
-                            self[i].update_tree_hash_cache(cache)?;
+                        vec[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();
+                            TreeHashCache::new(&vec[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();
@@ -175,14 +208,7 @@ where
 
     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(())
-    }
+    Ok(new_overlay)
 }
 
 fn get_packed_leaves<T>(vec: &Vec<T>) -> Result<Vec<u8>, Error>

eth2/utils/cached_tree_hash/src/lib.rs

@@ -4,7 +4,7 @@ use tree_hash::{TreeHash, TreeHashType, BYTES_PER_CHUNK, HASHSIZE};
 
 mod btree_overlay;
 mod errors;
-mod impls;
+pub mod impls;
 pub mod merkleize;
 mod resize;
 mod tree_hash_cache;

eth2/utils/tree_hash/src/impls.rs

@@ -56,11 +56,11 @@ impl TreeHash for [u8; 4] {
     }
 
     fn tree_hash_packed_encoding(&self) -> Vec<u8> {
-        panic!("bytesN should never be packed.")
+        unreachable!("bytesN should never be packed.")
     }
 
     fn tree_hash_packing_factor() -> usize {
-        panic!("bytesN should never be packed.")
+        unreachable!("bytesN should never be packed.")
     }
 
     fn tree_hash_root(&self) -> Vec<u8> {

eth2/utils/tree_hash/src/lib.rs

@@ -49,6 +49,7 @@ macro_rules! tree_hash_ssz_encoding_as_vector {
         }
     };
 }
+
 #[macro_export]
 macro_rules! tree_hash_ssz_encoding_as_list {
     ($type: ident) => {