Re: [stella] Qb: BETA 1.0

Subject: Re: [stella] Qb: BETA 1.0
From: Thomas Jentzsch <tjentzsch@xxxxxx>
Date: Sat, 3 Mar 2001 15:04:43 +0100
Andrew Davie wrote:
> ... sneaky.  I've not used this yet, as I've only JUST understood it.  Got
> the flu :(

Get well soon!

>> 9. exchange x and y here:
>> ZapPF   sta playfield,y

> I'm not sure what you're suggesting, and why, on the above.  Due to absolute
> addressing??

Yes, the 6502 has no opcode for sta ZP,y, so the compiler
uses sta ABS,y instead, which costs one byte. I'm
always trying to use x for zero-page RAM access and y
for reading ROM tables.
Look at the DASM listing file (just search for 00 in
the 3rd opcode column) and you might spot other places
(i.E. initscore) where you could optimize.

So, if you replace:
    sta playfield,y   ; = 3 bytes
    sta playfield,x   ; = 2 bytes

you will gain 2 bytes at ZapPF.

Have fun!
Thomas Jentzsch         | *** Every bit is sacred ! ***
tjentzsch at web dot de |

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