How do you do signed comparing statements in 65816

[undisbeliever]

I'm having a bit of trouble working with signed values in my SNES Small C Compiler. It currentaly supports unsigned values, but I want it to support signed variables.

Super Mario World uses signed values: As shown here

Code: Select all

LDA lifecounter
BMI +
CMP #99
BCS +
; do code here
+

This is the code to do a signed comparing on the life counter. (it first checks if it is neg then if it is less then 4 (I think)

Anyway, If the first value is in the stack and the second value is in the accumulator, how do I write a piece of code that will work in all situations???

[undisbeliever]

Currentally I'm using unsigned values.

With signed values (a == b) and (a != b) are the same, but when I use (a < b) it tends to get complicated.

This is what I currentlally have for unsigned value (assume 16 bit acc,index):

Code: Select all

;first value in stack
;next value in acc

  CMP $01,S  ;if(a < b)
  BGE +      ; = if(!(b >=a))
  LDA #$FFFF ;     true
  BRA ++
+            ;   else
  LDA #$0000 ;     false
++
  PLY

I'm thinking that I should be able to do this if I divide this into two sections, positive and negitive (but it starts etting confusing)

Can Any suggestions be made???

[anomie]

Have you tried that with BPL/BMI instead of BGE/BLT?

[undisbeliever]

That's the idea. I need to first check the sign of the two variables and then compare them, The above example is what I used for UNSIGNED values.