Thanks! There are much better indexing algorithms if you don't have such tight resource constraints, but it may be a useful trick to speed up inner loops in some other algorithms.

I realized yesterday that it can also be used as the basis for a linear-time sorting algorithm: https://gist.github.com/silentbicycle/8389129

Benchmarking indicates that it's probably not competitive speed-wise compared to counting sort (of which it is a variant), but the implementation should be pretty easy to understand. It may be good for pedagogical purposes.