(after much thought!)
I think the extra code complication is reasonable given the perormance requirement,  but I do think we should try not to make it *more* obscure than it already was -- if we aren't writing this software just for ourselves..

I tried adding a few comments myself to explain the 'tricky' bits, and it didn't seem that much
 -- check it out here : https://github.com/pp-mo/iris/commit/a8444da097cff9af1eab27437e413503eef2ffca

And actually, some of that can probably be reduced further.
Can you incorporate something like this, just as pointers to the key complications ?