zone: optimization of a frequently used function

src/knot/zone/node.c

@@ -193,15 +193,10 @@ int binode_prepare_change(zone_node_t *node, knot_mm_t *mm)
 
 zone_node_t *binode_node(zone_node_t *node, bool second)
 {
-	if (node != NULL && (node->flags & NODE_FLAGS_BINODE)) {
-		if (second && !(node->flags & NODE_FLAGS_SECOND)) {
-			return node + 1;
-		}
-		if (!second && (node->flags & NODE_FLAGS_SECOND)) {
-			return node - 1;
-		}
+	if (unlikely(node == NULL || !(node->flags & NODE_FLAGS_BINODE))) {
+		return node;
 	}
-	return node;
+	return node + (second - (int)((node->flags & NODE_FLAGS_SECOND) >> 9));
 }
 
 bool binode_rdata_shared(zone_node_t *node, uint16_t type)

src/knot/zone/node.h

@@ -85,9 +85,9 @@ enum node_flags {
 	/*! \brief Node is the zone Apex. */
 	NODE_FLAGS_APEX =            1 << 6,
 	/*! \brief Is this i bi-node? */
-	NODE_FLAGS_BINODE =          1 << 8,
+	NODE_FLAGS_BINODE =          1 << 8, // this value shall be fixed
 	/*! \brief Is this the second half of bi-node? */
-	NODE_FLAGS_SECOND =          1 << 9,
+	NODE_FLAGS_SECOND =          1 << 9, // this value shall be fixed
 	/*! \brief The node shall be deleted. It's just not because it's a bi-node and the counterpart still exists. */
 	NODE_FLAGS_DELETED =         1 << 10,
 };