I made one a 68010 emulator in C in 1994.

For the opcode dispatch, I made a file which consisted of regex and name pairs. The regexes matched strings of 0s and 1s: the bit patterns of the opcode space. The names mapped these to C functions. A script processed the file, generating the dispatch switch.

I seem to remember that on a 66 MHz 486 DX2 box running Linux, the thing was emulating about half a million instructions per second.

Code: totally lost to the sands of time.