Re: [stella] Re: Help with efficient code

Subject: Re: [stella] Re: Help with efficient code
From: jimn8@xxxxxxxxxx (Jim Nitchals)
Date: Mon, 29 Sep 1997 17:42:34 -0700 (PDT)
> 		beq  pointers,x

This isn't a valid instruction.  Conditional branches can only go to one
fixed location +/- 127 bytes away from the branch instruction itself.

If you have a single state in "VARIABLE", as your example did, try:

        lda variable
        cmp #num_entries
        bcs not_in_table
        lda jump_table,x
        sta temp     ; temp should be 2 bytes somewhere in RAM
        lda jump_table+1,x
        sta temp+1
        jmp (temp)   ; jump indirect through temp
; continue with rest of program

        dc.w framistat    ; your assembler may prefer .word
        dc.w dohickey
        dc.w whachamacallit
        dc.w thingy
        dc.w dodad
num_entries equ (*-jump_table)/2    ; some assemblers use $, not *
                                    ; to refer to current address
(or if all else fails:)
num_entries equ 5         ; but it isn't as nice

It's possible to rearrange the jump table into two halves (low and
high byte of the addresses in separate tables) but doing so only 
saves 1 instruction and makes the code harder to change.  Give this
method a try.

Archives updated once/day at
Unsubscribing and other info at

Current Thread