>Actually, the start of the function isn't that bad, but scroll down halfway and you'll find this: [...] Oh no, there's no way I'm going to be able to figure out all this byte manipulation in my head.

I know the author says later that they don't do C development, but note that most of this code is just reading two consecutive bytes as a 16-bit integer, except for x[9] and x[17] where the high bit has a special meaning.