Merge pull request #6394 from paritytech/trie_recursion

removed recursion from triedbmut::lookup

util/src/trie/triedbmut.rs

@@ -367,44 +367,50 @@ impl<'a> TrieDBMut<'a> {
 	}
 
 	// walk the trie, attempting to find the key's node.
-	fn lookup<'x, 'key>(&'x self, partial: NibbleSlice<'key>, handle: &NodeHandle) -> super::Result<Option<DBValue>>
+	fn lookup<'x, 'key>(&'x self, mut partial: NibbleSlice<'key>, handle: &NodeHandle) -> super::Result<Option<DBValue>>
 		where 'x: 'key
 	{
-		match *handle {
-			NodeHandle::Hash(ref hash) => Lookup {
+		let mut handle = handle;
+		loop {
+			let (mid, child) = match *handle {
+				NodeHandle::Hash(ref hash) => return Lookup {
 					db: &*self.db,
 					query: DBValue::from_slice,
 					hash: hash.clone(),
 				}.look_up(partial),
 				NodeHandle::InMemory(ref handle) => match self.storage[handle] {
-				Node::Empty => Ok(None),
+					Node::Empty => return Ok(None),
 					Node::Leaf(ref key, ref value) => {
 						if NibbleSlice::from_encoded(key).0 == partial {
-						Ok(Some(DBValue::from_slice(value)))
+							return Ok(Some(DBValue::from_slice(value)));
 						} else {
-						Ok(None)
+							return Ok(None);
 						}
 					}
 					Node::Extension(ref slice, ref child) => {
 						let slice = NibbleSlice::from_encoded(slice).0;
 						if partial.starts_with(&slice) {
-						self.lookup(partial.mid(slice.len()), child)
+							(slice.len(), child)
 						} else {
-						Ok(None)
+							return Ok(None);
 						}
 					}
 					Node::Branch(ref children, ref value) => {
 						if partial.is_empty() {
-						Ok(value.as_ref().map(|v| DBValue::from_slice(v)))
+							return Ok(value.as_ref().map(|v| DBValue::from_slice(v)));
 						} else {
 							let idx = partial.at(0);
 							match children[idx as usize].as_ref() {
-							Some(child) => self.lookup(partial.mid(1), child),
-							None => Ok(None),
+								Some(child) => (1, child),
+								None => return Ok(None),
 							}
 						}
 					}
 				}
+			};
+
+			partial = partial.mid(mid);
+			handle = child;
 		}
 	}