Interesting how the obfuscated code is explained by slowly unobfuscating it step by step. This is the reverse of how obfuscated code is normally created: by starting with understandable code, and then slowly obfuscating it bit by bit (as I explained for this IOCCC submission [1]).
I say normally because one could also have a superoptimizer search for a minimal program that achieves some desired behaviour, and then one has to understand it by slowly unraveling the generated code.