This library provides a C99 implementation of the Adaptive Radix Tree or ART. The ART operates similar to a traditional radix tree but avoids the wasted space of internal nodes by changing the node size. It makes use of 4 node sizes (4, 16, 48, 256), and can guarantee that the overhead is no more than 52 bytes per key, though in practice it is much lower.

As a radix tree, it provides the following:

• O(k) operations. In many cases, this can be faster than a hash table since the hash function is an O(k) operation, and hash tables have very poor cache locality.
• Minimum / Maximum value lookups
• Prefix compression
• Ordered iteration
• Prefix based iteration

Building the test code will generate errors if libcheck is not available. To build the test code successfully, do the following::

$ cd deps/check-0.9.8/
$ ./configure
$ make
# make install
# ldconfig (necessary on some Linux distros)
$ cd ../../
$ scons
$ ./test_runner

Or, if you prefer, you can skip the installation of libcheck and the test will adapt to it being in the tree (leave out make install):

 $ LD_LIBRARY_PATH=deps/check-0.9.8/src/.libs:. ./test_runner

This build will produce a test_runner executable for testing and a shared_object (libart.so on *NIX systems) for linking with.

Related works:

• The Adaptive Radix Tree: ARTful Indexing for Main-Memory Databases