Very cool! Writing emulators for simple CPUs is challenging enough because it's extremely easy to overlook a quirk or implement a flag calculation incorrectly that is used infrequently and have it silently lurking like a mine waiting for the rare piece of code to trip it. x86 is very complex. Instruction decoding alone looks like a nightmare. I guess the one saving grace here is that since most of us still run on x86, side-by-side validation is a lot easier.