If you want to write the most compact emulator, not necessarily the fastest, you can use the octal structure of the instruction encoding to condense your code greatly.

https://news.ycombinator.com/item?id=13045558

The first ~1/4 of the first-page opcode space is ALU ops, the next 1/4 is inc/dec/push/pop reg. The second half is less regular but you can still find big chunks that can be taken care of with only a few lines of code (e.g. 9x are exchanges with eAX, Bx are all immediate moves.)