Oh wow. That's beautifully done. Simple comments that explain clearly what the code is doing, pretty clear choice of variable names so little head-scratching going on.
The documentation of redis is really good for a large open source project. I am not a contributor, but still read the source code from time to time. Full credit to antirez for taking the time to make it easy to contribute to redis!
More remarkable is the fact that antirez updated the documentation in response to a post in Reddit. https://www.reddit.com/r/redis/comments/3re0aw/any_pointers_... Thank you antirez! :-)