Adding Preorder trversal

avl_tree.c

@@ -787,3 +787,35 @@ avl_tree_remove(struct avl_tree_node **root_ptr, struct avl_tree_node *node)
 							   -1, &left_deleted);
 	} while (parent);
 }
+
+/* Starts a preorder traversal of the tree.  */
+struct avl_tree_node *
+avl_tree_first_in_preorder(const struct avl_tree_node *root)
+{
+	return (struct avl_tree_node *)root;
+}
+
+/* Continues a preorder traversal of the tree. @prev_parent must be its saved
+ * parent node.  Returns NULL if there are no more nodes (i.e. @prev was the
+ * root of the tree).  */
+struct avl_tree_node *
+avl_tree_next_in_preorder(const struct avl_tree_node *prev,
+			   const struct avl_tree_node *prev_parent)
+{
+    const struct avl_tree_node *next = NULL;
+
+    if (prev && (prev->left || prev->right))
+        next = prev->left ? prev->left : prev->right;
+    else
+        for (;
+            prev_parent;
+            prev = prev_parent, prev_parent = avl_get_parent(prev_parent))
+            if (prev_parent->right && prev_parent->right != prev)
+            {
+                next = prev_parent->right;
+                break;
+            }
+
+    return (struct avl_tree_node *)next;
+}
+

avl_tree.h

@@ -285,6 +285,13 @@ avl_tree_next_in_order(const struct avl_tree_node *node);
 extern struct avl_tree_node *
 avl_tree_prev_in_order(const struct avl_tree_node *node);
 
+extern struct avl_tree_node *
+avl_tree_first_in_preorder(const struct avl_tree_node *root);
+
+extern struct avl_tree_node *
+avl_tree_next_in_preorder(const struct avl_tree_node *prev,
+			   const struct avl_tree_node *prev_parent);
+
 extern struct avl_tree_node *
 avl_tree_first_in_postorder(const struct avl_tree_node *root);
 
@@ -342,18 +349,33 @@ avl_tree_next_in_postorder(const struct avl_tree_node *prev,
 				     struct_member), 1);		\
 	     _cur = avl_tree_prev_in_order(_cur))
 
+
+#define avl_tree_for_each(child_struct, root,       \
+                       struct_name, struct_member, order)  \
+	for (struct avl_tree_node *_cur =				\
+		avl_tree_first_in_##order(root), *_parent;		\
+	     _cur && ((child_struct) =					\
+		      avl_tree_entry(_cur, struct_name,			\
+				     struct_member), 1)			\
+	          && (_parent = avl_get_parent(_cur), 1);		\
+	     _cur = avl_tree_next_in_##order(_cur, _parent))
+
 /*
  * Like avl_tree_for_each_in_order(), but iterates through the nodes in
  * postorder, so the current node may be deleted or freed.
  */
 #define avl_tree_for_each_in_postorder(child_struct, root,		\
+                       struct_name, struct_member)	\
+    avl_tree_for_each(child_struct, root,       \
+                       struct_name, struct_member, postorder)
+
+/*
+ * Like avl_tree_for_each_in_order(), but iterates through the nodes in
+ * preorder.
+ */
+#define avl_tree_for_each_in_preorder(child_struct, root,		\
 				       struct_name, struct_member)	\
-	for (struct avl_tree_node *_cur =				\
-		avl_tree_first_in_postorder(root), *_parent;		\
-	     _cur && ((child_struct) =					\
-		      avl_tree_entry(_cur, struct_name,			\
-				     struct_member), 1)			\
-	          && (_parent = avl_get_parent(_cur), 1);		\
-	     _cur = avl_tree_next_in_postorder(_cur, _parent))
+    avl_tree_for_each(child_struct, root,       \
+                       struct_name, struct_member, preorder)
 
 #endif /* _AVL_TREE_H_ */

test.c

@@ -192,6 +192,20 @@ verify(const int *data, int count)
 		assert(!cur->right  || TEST_NODE(cur->right)->reached);
 	}
 	assert(x == count);
+
+	/* Check preorder traversal.  */
+	for (cur = avl_tree_first_in_preorder(root), x = 0;
+	     cur;
+	     cur = avl_tree_next_in_preorder(cur, avl_get_parent(cur)), x++)
+	{
+		assert(TEST_NODE(cur)->reached);
+		TEST_NODE(cur)->reached = 0;
+		assert(!avl_get_parent(cur) ||
+		       !(TEST_NODE(avl_get_parent(cur))->reached));
+		assert(!cur->left   || TEST_NODE(cur->left)->reached);
+		assert(!cur->right  || TEST_NODE(cur->right)->reached);
+	}
+	assert(x == count);
 }
 #endif