It's probably worth noting that this is only a runtime assembler, i.e. it does no parsing. It also doesn't support all of the addressing modes for the instructions that it does support. Nonetheless it does show that assemblers aren't that hard. Adding support for the various addressing modes and amd64 does complicate things but not too badly. Moving forward from this you'd probably want a better scheme for handling the various "extra" bytes (SIB, REX, etc.).
It's probably worth noting that this is only a runtime assembler, i.e. it does no parsing. It also doesn't support all of the addressing modes for the instructions that it does support. Nonetheless it does show that assemblers aren't that hard. Adding support for the various addressing modes and amd64 does complicate things but not too badly. Moving forward from this you'd probably want a better scheme for handling the various "extra" bytes (SIB, REX, etc.).