atari2600land's Blog

If you're using Assembly Language, then you should be able to do something similar to the "Select Case" or "On X Goto" statement in BASIC dialects. As a matter of fact, such "switch" statements are just very slightly removed from Assembly's dispatch tables.

 

I do not know your specific Assembly dialect, but the typical construct is something like this (in pseudo code):

  1. Move In Value to Register
  2. Add base address of dispatch table to Register
  3. Move In address pointed to by Register (indirect mode) to Program Counter

If your language does not support moving an address from a Register to the Program Counter then:
  3. Move In address pointed to by Register (indirect mode) to Index Register
  4. Branch to Index Register

I hope that helps!

 

-dZ.

The Dispatch Table is just an array of addresses to the individual procedures.

 

Basically, you are using the value of a variable as an index into the array, and jumping to that address.