BOSTree -- An order statistic, self-balancing AVL tree implementation in C

An order statistic tree is a tree structure with two additional methods,
rank(node) and select(index), which allow array-like access in O(log n) time.
The idea is to simply store, for each node, the number of child-nodes.
Self-balancing search trees maintain a minimal height by rebalancing their
sub-trees.

I did not find a C reference implementation for such a tree, so I wrote one
myself. This implementation uses map semantics, that is, stores key and value
as separate pointers.

It stores some not strictly necessary numbers, such as the number of sub-nodes
of the right child of a node. This allows to calculate the overall count
quickly, but can be removed to make the structure's overhead smaller.

The code has been extensively tested, is apparently AFL-proof, and leaks no
memory whatsoever according to valgrind. BOSTree has been in use in pqiv for
some time now.


ALTERNATIVES:

· In GNU/C++, Policy-Based Data Structures can be used according to
  http://stackoverflow.com/questions/11230734/c-stl-order-statistic-tree
  That code probably is much more mature. Use it if this is an option!

· If you do not need the order statistic part, there are plenty of balanced
  tree implementations which suit your use case better. They are better tested
  and much faster because they do not have the overhead of order statistics. For
  example, see glib:
  https://developer.gnome.org/glib/stable/glib-Balanced-Binary-Trees.html

· glib appears to have a concealed order statistic balanced binary tree
  implementation, only they name this sequences:
  https://developer.gnome.org/glib/stable/glib-Sequences.html


Licensed under the terms of the GPLv3.