feat: reorganise extension node insertion to use separate pointers fo…

…r the child node

proofs.go

@@ -193,17 +193,6 @@ func (proof *SparseMerkleClosestProof) Unmarshal(bz []byte) error {
 	return dec.Decode(proof)
 }
 
-// GetValueHash returns the value hash of the closest proof.
-func (proof *SparseMerkleClosestProof) GetValueHash(spec *TrieSpec) []byte {
-	if proof.ClosestValueHash == nil {
-		return nil
-	}
-	if spec.sumTrie {
-		return proof.ClosestValueHash[:len(proof.ClosestValueHash)-sumSize]
-	}
-	return proof.ClosestValueHash
-}
-
 func (proof *SparseMerkleClosestProof) validateBasic(spec *TrieSpec) error {
 	// ensure the depth of the leaf node being proven is within the path size
 	if proof.Depth < 0 || proof.Depth > spec.ph.PathSize()*8 {

smt.go

@@ -178,19 +178,36 @@ func (smt *SMT) update(
 		}
 		// We insert an "extension" representing multiple single-branch inner nodes
 		last := &node
+		var newInner *innerNode
+		if getPathBit(path, prefixlen) == left {
+			newInner = &innerNode{
+				leftChild:  newLeaf,
+				rightChild: leaf,
+			}
+		} else {
+			newInner = &innerNode{
+				leftChild:  leaf,
+				rightChild: newLeaf,
+			}
+		}
+		// Determine if we need to insert an extension or a branch
 		if depth < prefixlen {
 			// note: this keeps path slice alive - GC inefficiency?
 			if depth > 0xff {
 				panic("invalid depth")
 			}
-			ext := extensionNode{path: path, pathBounds: [2]byte{byte(depth), byte(prefixlen)}}
+			ext := extensionNode{
+				child: newInner,
+				path:  path,
+				pathBounds: [2]byte{
+					byte(depth), byte(prefixlen),
+				},
+			}
+			// Dereference the last node to replace it with the extension node
 			*last = &ext
-			last = &ext.child
-		}
-		if getPathBit(path, prefixlen) == left {
-			*last = &innerNode{leftChild: newLeaf, rightChild: leaf}
 		} else {
-			*last = &innerNode{leftChild: leaf, rightChild: newLeaf}
+			// Dereference the last node to replace it with the new inner node
+			*last = newInner
 		}
 		return node, nil
 	}