Create cached_tree_hash crate.

eth2/utils/cached_tree_hash/src/lib.rs

@@ -0,0 +1,66 @@
+use hashing::hash;
+use std::ops::Range;
+use tree_hash::{TreeHash, TreeHashType, BYTES_PER_CHUNK, HASHSIZE};
+
+mod btree_overlay;
+mod errors;
+mod impls;
+pub mod merkleize;
+mod resize;
+mod tree_hash_cache;
+
+pub use btree_overlay::BTreeOverlay;
+pub use errors::Error;
+pub use tree_hash_cache::TreeHashCache;
+
+pub trait CachedTreeHash<Item>: TreeHash {
+    fn tree_hash_cache_overlay(
+        &self,
+        chunk_offset: usize,
+        depth: usize,
+    ) -> Result<BTreeOverlay, Error>;
+
+    fn num_tree_hash_cache_chunks(&self) -> usize;
+
+    fn new_tree_hash_cache(&self, depth: usize) -> Result<TreeHashCache, Error>;
+
+    fn update_tree_hash_cache(&self, cache: &mut TreeHashCache) -> Result<(), Error>;
+}
+
+#[derive(Debug, PartialEq)]
+pub struct CachedTreeHasher {
+    cache: TreeHashCache,
+}
+
+impl CachedTreeHasher {
+    pub fn new<T>(item: &T) -> Result<Self, Error>
+    where
+        T: CachedTreeHash<T>,
+    {
+        Ok(Self {
+            cache: TreeHashCache::new(item, 0)?,
+        })
+    }
+
+    pub fn update<T>(&mut self, item: &T) -> Result<(), Error>
+    where
+        T: CachedTreeHash<T>,
+    {
+        // Reset the per-hash counters.
+        self.cache.chunk_index = 0;
+        self.cache.overlay_index = 0;
+
+        // Reset the "modified" flags for the cache.
+        self.cache.reset_modifications();
+
+        // Update the cache with the (maybe) changed object.
+        item.update_tree_hash_cache(&mut self.cache)?;
+
+        Ok(())
+    }
+
+    pub fn tree_hash_root(&self) -> Result<Vec<u8>, Error> {
+        // Return the root of the cache -- the merkle root.
+        Ok(self.cache.root()?.to_vec())
+    }
+}