Making Trie.iter non-recursive (#2733)

util/benches/trie.rs

@@ -21,7 +21,7 @@ extern crate ethcore_util;
 #[macro_use]
 extern crate log;
 
-use test::Bencher;
+use test::{Bencher, black_box};
 use ethcore_util::hash::*;
 use ethcore_util::bytes::*;
 use ethcore_util::trie::*;
@@ -78,6 +78,32 @@ fn trie_insertions_32_mir_1k(b: &mut Bencher) {
 	});
 //	println!("hash_count: {}", hash_count);
 }
+#[bench]
+fn trie_iter(b: &mut Bencher) {
+	let st = StandardMap {
+		alphabet: Alphabet::All,
+		min_key: 32,
+		journal_key: 0,
+		value_mode: ValueMode::Mirror,
+		count: 1000,
+	};
+	let d = st.make();
+	let mut memdb = MemoryDB::new();
+	let mut root = H256::new();
+	{
+		let mut t = TrieDBMut::new(&mut memdb, &mut root);
+		for i in d.iter() {
+			t.insert(&i.0, &i.1).unwrap();
+		}
+	}
+
+	b.iter(&mut ||{
+		let t = TrieDB::new(&memdb, &root).unwrap();
+		for n in t.iter().unwrap() {
+			black_box(n).unwrap();
+		}
+	});
+}
 
 #[bench]
 fn triehash_insertions_32_mir_1k(b: &mut Bencher) {

util/src/trie/triedb.rs

@@ -304,14 +304,6 @@ impl<'a> TrieDBIterator<'a> {
 		Ok(())
 	}
 
-	/// Descend into a payload and get the next item.
-	fn descend_next(&mut self, d: &'a [u8]) -> Option<TrieItem<'a>> {
-		match self.descend(d) {
-			Ok(()) => self.next(),
-			Err(e) => Some(Err(e)),
-		}
-	}
-
 	/// The present key.
 	fn key(&self) -> Bytes {
 		// collapse the key_nibbles down to bytes.
@@ -323,6 +315,7 @@ impl<'a> Iterator for TrieDBIterator<'a> {
 	type Item = TrieItem<'a>;
 
 	fn next(&mut self) -> Option<Self::Item> {
+		loop {
 			let b = match self.trail.last_mut() {
 				Some(mut b) => { b.increment(); b.clone() },
 				None => return None,
@@ -338,26 +331,39 @@ impl<'a> Iterator for TrieDBIterator<'a> {
 						_ => {}
 					}
 					self.trail.pop();
-				self.next()
+					// continue
 				},
-			(Status::At, Node::Leaf(_, v)) | (Status::At, Node::Branch(_, Some(v))) => Some(Ok((self.key(), v))),
-			(Status::At, Node::Extension(_, d)) => self.descend_next(d),
-			(Status::At, Node::Branch(_, _)) => self.next(),
+				(Status::At, Node::Leaf(_, v)) | (Status::At, Node::Branch(_, Some(v))) => {
+					return Some(Ok((self.key(), v)));
+				},
+				(Status::At, Node::Extension(_, d)) => {
+					if let Err(e) = self.descend(d) {
+						return Some(Err(e));
+					}
+					// continue
+				},
+				(Status::At, Node::Branch(_, _)) => {},
 				(Status::AtChild(i), Node::Branch(children, _)) if children[i].len() > 0 => {
 					match i {
 						0 => self.key_nibbles.push(0),
 						i => *self.key_nibbles.last_mut().unwrap() = i as u8,
 					}
-				self.descend_next(children[i])
+					if let Err(e) = self.descend(children[i]) {
+						return Some(Err(e));
+					}
+					// continue
 				},
 				(Status::AtChild(i), Node::Branch(_, _)) => {
-				if i == 0 { self.key_nibbles.push(0); }
-				self.next()
+					if i == 0 {
+						self.key_nibbles.push(0);
+					}
+					// continue
 				},
 				_ => panic!() // Should never see Entering or AtChild without a Branch here.
 			}
 		}
 	}
+}
 
 impl<'db> Trie for TrieDB<'db> {
 	fn iter<'a>(&'a self) -> super::Result<Box<Iterator<Item = TrieItem> + 'a>> {