wavltree is a portable, easy-to-use C language balanced binary search tree,
using the rebalancing weak AVL algorithm described in [Haeupler et. al][1].
The weak AVL (or wavl for short) tree is a relaxation of the constraints enforced on AVL trees. This relaxation permits much less complex rebalancing of the tree after node removals than what AVL trees enforce, giving a wavl tree worst case performance similar to a red-black tree for workloads that include a mix of deletions.
For workloads that are insertion-only, the worst case search time for a wavl tree is equivalent to that of an AVL tree, with a slightly less complex set of rebalancing operations.
Not all wavl trees are AVL trees (but those that are insertion-only are), but interestingly, all wavl trees are valid red-black trees. Red-Black trees, however, are a superset of wavl trees. Thus, not all red-black trees are valid wavl trees. How's that for an interesting result?
The wavl tree implementation uses an embedded state struct that contains 3 pointers and a boolean value to indicate the rank parity of the current node.
The rank parity could fairly easily be encoded as a high-order bit in one of these pointers. The groundwork, sort of, has been laid by not having any of the main algorithms refer to the rank parity field directly, but there is still some work to be done.
The wavltree library depends only on the C standard library. The code is
written to compile with any C99-capable compiler. If you want to use wavltree
as a part of your project, you can simply copy wavltree.c into your project,
and put wavltree.h and wavltree_priv.h wherever you keep your project's
headers.
All functions and structures have Doxygen documentation describing members, any library-level functions and their usage.
The wavltree implementation is licensed under a 2-clause BSD-style license.
For more information, please see the COPYING file in the project directory.
Phil got nerd sniped. :-(
- Haeupler, Sen, Tarjan, "Rank-Balanced Trees" (see [http://sidsen.azurewebsites.net//papers/rb-trees-talg.pdf])