Move to using function-pointers.

[skx]

Rather than having a giant switch statement, with a case for each opcode, we should break out the implementations of the opcodes into their own functions.

If we define an array of 255-opcodes in the svm_t function then we can use function pointers to invoke the correct function.

• Pros
  • The code becomes more readable.
  • We could have a default handler which dumps "unknown instruction" for debugging purposes.
  • This would allow host-applications to define host-specific opcodes.
• Cons
  • Significant churn.
  • Wastes 255 * (function-pointer size) bytes per svm_t instance.
  • We have some repetition setting up the opcode handlers - both defining the function and then allocating it.

[skx]

I have a workable proof of concept at the moment, but there are implications I'd not forseen.

• The "running" flag isn't accessible to the op_exit primitive, so it must be moved to part of the CPU-state.
• The use of the restart label (+ associated goto) to allow updating IP via jump instructions won't work.

For the moment I've updated my operations signature to this:

Bool op_foo( void * input );

If that function returns TRUE then it is assumed IP has been updated and it is left alone, otherwise it increments appropriately. This works but it feels a little unclean.

Will commit shortly. Just tweaking the emacs macro to mass-edit ;)