Directory Restructure (#1163)

* Move tests -> testing

* Directory restructure

* Update Cargo.toml during restructure

* Update Makefile during restructure

* Fix arbitrary path

consensus/cached_tree_hash/src/lib.rs

@@ -0,0 +1,47 @@
+mod cache;
+mod cache_arena;
+mod impls;
+#[cfg(test)]
+mod test;
+use smallvec::SmallVec;
+
+type SmallVec8<T> = SmallVec<[T; 8]>;
+pub type CacheArena = cache_arena::CacheArena<Hash256>;
+
+pub use crate::cache::TreeHashCache;
+pub use crate::impls::int_log;
+use ethereum_types::H256 as Hash256;
+use tree_hash::TreeHash;
+
+#[derive(Debug, PartialEq, Clone)]
+pub enum Error {
+    /// Attempting to provide more than 2^depth leaves to a Merkle tree is disallowed.
+    TooManyLeaves,
+    /// Shrinking a Merkle tree cache by providing it with less leaves than it currently has is
+    /// disallowed (for simplicity).
+    CannotShrink,
+    /// Cache is inconsistent with the list of dirty indices provided.
+    CacheInconsistent,
+    CacheArenaError(cache_arena::Error),
+    /// Unable to find left index in Merkle tree.
+    MissingLeftIdx(usize),
+}
+
+impl From<cache_arena::Error> for Error {
+    fn from(e: cache_arena::Error) -> Error {
+        Error::CacheArenaError(e)
+    }
+}
+
+/// Trait for types which can make use of a cache to accelerate calculation of their tree hash root.
+pub trait CachedTreeHash<Cache>: TreeHash {
+    /// Create a new cache appropriate for use with values of this type.
+    fn new_tree_hash_cache(&self, arena: &mut CacheArena) -> Cache;
+
+    /// Update the cache and use it to compute the tree hash root for `self`.
+    fn recalculate_tree_hash_root(
+        &self,
+        arena: &mut CacheArena,
+        cache: &mut Cache,
+    ) -> Result<Hash256, Error>;
+}