> Can someone please find _and_ explain it to me? :-)
Well, this isn't an eor-trick. But fairly efficient.
Depends on what's your poison... code size or speed.
ldy FrameCounter
lda NextFrame,y
sta FrameCounter
NextFrame
.byte 1,2,0
That's just about the quickest I know... 10 cycles
It also uses 10 bytes.
How about this one....
lda FrameCounter
cmp #2
adc #1
and #3
sta FrameCounter
That's pretty cool! If the number is < 2 (ie 0 or 1) it will clear the
carry, and just add 1.
If its >=2 (ie: 2) it will set the carry, therefore adding two - taking it
to 4
The and with 3 will then restore that to 0
Not better than the first version, though. This one is 12 cycles and 10
bytes.
Still, fun :)
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----- Original Message -----
From: "Manuel Polik" <manuel.polik@xxxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Wednesday, March 07, 2001 10:02 PM
Subject: [stella] Very BASIC ASM Info needed...
> Mornin'
>
> Supposed I want to have a counter which does 0/1/2 and then repeats.
> Straightforward everybody will come up with something like this:
>
> INC frameCounter
> LDA frameCounter
> CMP #$03
> BNE CounterOk
> LDA #$00
> STA frameCounter
>
> Now, I'm almost 100% certain, that there must be a more elegant EOR
> trick here.
>
> Can someone please find _and_ explain it to me? :-)
>
> Greetings,
> Manuel
>
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