Move tree_hash from ssz into own crate

eth2/utils/tree_hash/src/impls.rs

@@ -0,0 +1,239 @@
+use super::resize::{grow_merkle_cache, shrink_merkle_cache};
+use super::*;
+use ssz::ssz_encode;
+
+impl CachedTreeHash<u64> for u64 {
+    fn item_type() -> ItemType {
+        ItemType::Basic
+    }
+
+    fn build_tree_hash_cache(&self) -> Result<TreeHashCache, Error> {
+        Ok(TreeHashCache::from_bytes(
+            merkleize(ssz_encode(self)),
+            false,
+        )?)
+    }
+
+    fn num_bytes(&self) -> usize {
+        8
+    }
+
+    fn offsets(&self) -> Result<Vec<usize>, Error> {
+        Err(Error::ShouldNotProduceBTreeOverlay)
+    }
+
+    fn num_child_nodes(&self) -> usize {
+        0
+    }
+
+    fn packed_encoding(&self) -> Vec<u8> {
+        ssz_encode(self)
+    }
+
+    fn packing_factor() -> usize {
+        32 / 8
+    }
+
+    fn cached_hash_tree_root(
+        &self,
+        other: &Self,
+        cache: &mut TreeHashCache,
+        chunk: usize,
+    ) -> Result<usize, Error> {
+        if self != other {
+            let leaf = merkleize(ssz_encode(self));
+            cache.modify_chunk(chunk, &leaf)?;
+        }
+
+        Ok(chunk + 1)
+    }
+}
+
+impl<T> CachedTreeHash<Vec<T>> for Vec<T>
+where
+    T: CachedTreeHash<T>,
+{
+    fn item_type() -> ItemType {
+        ItemType::List
+    }
+
+    fn build_tree_hash_cache(&self) -> Result<TreeHashCache, Error> {
+        match T::item_type() {
+            ItemType::Basic => TreeHashCache::from_bytes(merkleize(get_packed_leaves(self)), false),
+            ItemType::Composite | ItemType::List => {
+                let subtrees = self
+                    .iter()
+                    .map(|item| TreeHashCache::new(item))
+                    .collect::<Result<Vec<TreeHashCache>, _>>()?;
+
+                TreeHashCache::from_leaves_and_subtrees(self, subtrees)
+            }
+        }
+    }
+
+    fn offsets(&self) -> Result<Vec<usize>, Error> {
+        let offsets = match T::item_type() {
+            ItemType::Basic => vec![1; self.len() / T::packing_factor()],
+            ItemType::Composite | ItemType::List => {
+                let mut offsets = vec![];
+
+                for item in self {
+                    offsets.push(BTreeOverlay::new(item, 0)?.total_nodes())
+                }
+
+                offsets
+            }
+        };
+
+        Ok(offsets)
+    }
+
+    fn num_child_nodes(&self) -> usize {
+        // TODO
+        42
+    }
+
+    fn num_bytes(&self) -> usize {
+        self.iter().fold(0, |acc, item| acc + item.num_bytes())
+    }
+
+    fn packed_encoding(&self) -> Vec<u8> {
+        panic!("List should never be packed")
+    }
+
+    fn packing_factor() -> usize {
+        1
+    }
+
+    fn cached_hash_tree_root(
+        &self,
+        other: &Vec<T>,
+        cache: &mut TreeHashCache,
+        chunk: usize,
+    ) -> Result<usize, Error> {
+        let offset_handler = BTreeOverlay::new(self, chunk)?;
+        let old_offset_handler = BTreeOverlay::new(other, chunk)?;
+
+        if offset_handler.num_leaf_nodes != old_offset_handler.num_leaf_nodes {
+            let old_offset_handler = BTreeOverlay::new(other, chunk)?;
+
+            // Get slices of the exsiting tree from the cache.
+            let (old_bytes, old_flags) = cache
+                .slices(old_offset_handler.chunk_range())
+                .ok_or_else(|| Error::UnableToObtainSlices)?;
+
+            let (new_bytes, new_flags) =
+                if offset_handler.num_leaf_nodes > old_offset_handler.num_leaf_nodes {
+                    grow_merkle_cache(
+                        old_bytes,
+                        old_flags,
+                        old_offset_handler.height(),
+                        offset_handler.height(),
+                    )
+                    .ok_or_else(|| Error::UnableToGrowMerkleTree)?
+                } else {
+                    shrink_merkle_cache(
+                        old_bytes,
+                        old_flags,
+                        old_offset_handler.height(),
+                        offset_handler.height(),
+                        offset_handler.total_chunks(),
+                    )
+                    .ok_or_else(|| Error::UnableToShrinkMerkleTree)?
+                };
+
+            // Create a `TreeHashCache` from the raw elements.
+            let modified_cache = TreeHashCache::from_elems(new_bytes, new_flags);
+
+            // Splice the newly created `TreeHashCache` over the existing elements.
+            cache.splice(old_offset_handler.chunk_range(), modified_cache);
+        }
+
+        match T::item_type() {
+            ItemType::Basic => {
+                let leaves = get_packed_leaves(self);
+
+                for (i, chunk) in offset_handler.iter_leaf_nodes().enumerate() {
+                    if let Some(latest) = leaves.get(i * HASHSIZE..(i + 1) * HASHSIZE) {
+                        cache.maybe_update_chunk(*chunk, latest)?;
+                    }
+                }
+                let first_leaf_chunk = offset_handler.first_leaf_node()?;
+
+                cache.splice(
+                    first_leaf_chunk..offset_handler.next_node,
+                    TreeHashCache::from_bytes(leaves, true)?,
+                );
+            }
+            ItemType::Composite | ItemType::List => {
+                let mut i = offset_handler.num_leaf_nodes;
+                for &start_chunk in offset_handler.iter_leaf_nodes().rev() {
+                    i -= 1;
+                    match (other.get(i), self.get(i)) {
+                        // The item existed in the previous list and exsits in the current list.
+                        (Some(old), Some(new)) => {
+                            new.cached_hash_tree_root(old, cache, start_chunk)?;
+                        }
+                        // The item existed in the previous list but does not exist in this list.
+                        //
+                        // I.e., the list has been shortened.
+                        (Some(old), None) => {
+                            // Splice out the entire tree of the removed node, replacing it with a
+                            // single padding node.
+                            let end_chunk = BTreeOverlay::new(old, start_chunk)?.next_node();
+
+                            cache.splice(
+                                start_chunk..end_chunk,
+                                TreeHashCache::from_bytes(vec![0; HASHSIZE], true)?,
+                            );
+                        }
+                        // The item existed in the previous list but does exist in this list.
+                        //
+                        // I.e., the list has been lengthened.
+                        (None, Some(new)) => {
+                            let bytes: Vec<u8> = TreeHashCache::new(new)?.into();
+
+                            cache.splice(
+                                start_chunk..start_chunk + 1,
+                                TreeHashCache::from_bytes(bytes, true)?,
+                            );
+                        }
+                        // The item didn't exist in the old list and doesn't exist in the new list,
+                        // nothing to do.
+                        (None, None) => {}
+                    };
+                }
+            }
+        }
+
+        for (&parent, children) in offset_handler.iter_internal_nodes().rev() {
+            if cache.either_modified(children)? {
+                cache.modify_chunk(parent, &cache.hash_children(children)?)?;
+            }
+        }
+
+        // If the root node or the length has changed, mix in the length of the list.
+        let root_node = offset_handler.root();
+        if cache.changed(root_node)? | (self.len() != other.len()) {
+            cache.modify_chunk(root_node, &cache.mix_in_length(root_node, self.len())?)?;
+        }
+
+        Ok(offset_handler.next_node())
+    }
+}
+
+fn get_packed_leaves<T>(vec: &Vec<T>) -> Vec<u8>
+where
+    T: CachedTreeHash<T>,
+{
+    let num_packed_bytes = vec.num_bytes();
+    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.packed_encoding());
+    }
+
+    sanitise_bytes(packed)
+}