From d1fb6e1f55c603241e1180f5ec80b5fd8b5f4aaf Mon Sep 17 00:00:00 2001
From: Roy Crihfield <roy@manteia.ltd>
Date: Wed, 6 Sep 2023 20:12:59 +0800
Subject: [PATCH] symdiff - skip identical subtrees

---
 utils/iterator.go      | 10 +++++-----
 utils/iterator_test.go |  2 +-
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/utils/iterator.go b/utils/iterator.go
index a2486df..d02cff7 100644
--- a/utils/iterator.go
+++ b/utils/iterator.go
@@ -138,10 +138,13 @@ func (it *symmDiffIterator) seek() {
 			it.yieldFromA = false
 			return
 		case 0:
-			if it.a.Next(true) {
+			// if A and B have the same path and non-zero hash, they are identical and we can skip
+			// the whole subtree
+			noHash := it.a.Hash() == common.Hash{}
+			if it.a.Next(noHash) {
 				it.count++
 			}
-			if it.b.Next(true) {
+			if it.b.Next(noHash) {
 				it.count++
 			}
 		}
@@ -156,9 +159,6 @@ func (it *symmDiffIterator) Error() error {
 }
 
 func compareNodes(a, b trie.NodeIterator) int {
-	// if cmp := bytes.Compare(a.Path(), b.Path()); cmp != 0 {
-	// 	return cmp
-	// }
 	if a.Leaf() && !b.Leaf() {
 		return -1
 	} else if b.Leaf() && !a.Leaf() {
diff --git a/utils/iterator_test.go b/utils/iterator_test.go
index 3473c63..0ce0078 100644
--- a/utils/iterator_test.go
+++ b/utils/iterator_test.go
@@ -50,7 +50,7 @@ func TestSymmetricDifferenceIterator(t *testing.T) {
 		for di.Next(true) {
 			t.Errorf("iterator should not yield any elements")
 		}
-		assert.Equal(t, 4, *count)
+		assert.Equal(t, 2, *count)
 
 		trieb := trie.NewEmpty(db)
 		di, count = utils.NewSymmetricDifferenceIterator(triea.NodeIterator([]byte("food")), trieb.NodeIterator(nil))