> Initialize FrameCounter to 00x01x10 (x doesn't matter), then do:
That's a pretty neat trick, Russ.... you can drop the clc and replace the
first rol by an asl (saving a byte, and 2 cycles)
lda FrameCounter
asl
rol
rol
sta FrameCounter
I think, though, that we should count the extra cycles to trim off the low
bits and transfer to an index register - the table lookup is a clear winner
when this is taken into account. But still, your idea... at just 7 bytes...
very impressive!
Cheers
A
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----- Original Message -----
From: "Russ Perry Jr" <slapdash@xxxxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Thursday, March 08, 2001 4:54 PM
Subject: Re: [stella] Very BASIC ASM Info needed...
> At 10:25 PM +1100 3/7/01, Andrew Davie wrote:
> >How about this one....
> >
> > lda FrameCounter
> > cmp #2
> > adc #1
> > and #3
> > sta FrameCounter
> >
> >Not better than the first version, though. This one is 12 cycles and 10
> >bytes.
>
> I'm not up on counting, as I don't really know 6502 assembly...
> I guess the LDA and STA are two bytes each and 3 cycles because
> they are using FrameCounter in zeropage?
>
> Anyway, I started thinking there was another way, and I guess there
> is, though it isn't quicker...
>
> Initialize FrameCounter to 00x01x10 (x doesn't matter), then do:
>
> lda FrameCounter
> clc
> rol
> rol
> rol
> sta FrameCounter
>
> If I counted right, that's 14 cycles, but only 8 bytes. If you need
> more room than time...
> --
> //*================================================================++
> || Russ Perry Jr 2175 S Tonne Dr #114 Arlington Hts IL 60005 ||
> || 847-952-9729 slapdash@xxxxxxxxxxxx VIDEOGAME COLLECTOR! ||
> ++================================================================*//
>
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