This is one I saw in another thread that made me scratch my head for a while is using add dx,dx to simultaneously test and clear a "flag". For example you have a loop where you are setting a flag from 0 to 1 if something occurred. Then at the end of the loop you check the flag to see if you need to loop again and reset the flag (sorting routine I did this in).
Instead of:
Code:
.loop:
moveq #0,d0 ;reset flag
...
;If something occured, flag it
moveq #1,d0
...
;Do we need to loop again?
tst.w d0
bne.s .loop
Do this:
Code:
moveq #0,d0 ;reset flag once
.loop:
...
;If something occured, flag it
moveq #-128,d0 ;set flag = $80 ($fffffff80)
...
;Do we need to loop again? Also reset flag
add.b d0,d0
bcs.s .loop
Can do the same thing with subq and bmi, but I liked the use of carry
