Aw: Aw: [stella] Playfield ram usage

Subject: Aw: Aw: [stella] Playfield ram usage
From: cybergoth@xxxxxxxx
Date: Wed, 22 Aug 2001 10:39:55 +0200 (CEST)
Hi Glenn!

Uhm... forget what I wrote in the other mail. You'll have the tombstones
appear/disappear while playing a level, right?

What about not limiting the # but the possible positions instead?
Let's say you've only one tombstone per PF byte?
Then you'd have a simple table like:

PFVals:
     .byte %00000001
     .byte %00000010
     .byte %00000100
     .byte %00001000
     .byte %00010000
     .byte %00100000
     .byte %01000000
     .byte %10000000

Now you'd only need 3 bit to decode your data. Hm... add another 8 vals...

PFVals:
     .byte %00000001\
     .byte %00000010
     .byte %00000100
     .byte %00001000  one tomstone
     .byte %00010000
     .byte %00100000
     .byte %01000000
     .byte %10000000/
     .byte %00010001\
     .byte %00100010
     .byte %01000100
     .byte %10001000  two tombstones
     .byte %00010001
     .byte %00100010
     .byte %01000100
     .byte %10001000/

Ok, now we need 4 Bit to decode PF areas with 1 or 2 tombstones.
That reduces your byte usage by 50% and shouldn't be too hard to
unpack. Uhm... I've a very dirty trick... might work... do the
table like this:

ORG FX00 ; 16 low nibbles
PFVals:
     .byte %00000001\
     .byte %00000010
     .byte %00000100
     .byte %00001000  one tomstone
     .byte %00010000
     .byte %00100000
     .byte %01000000
     .byte %10000000/
     .byte %00010001\
     .byte %00100010
     .byte %01000100
     .byte %10001000  two tombstones
     .byte %00010001
     .byte %00100010
     .byte %01000100
     .byte %10001000/

ORG FX10 ; first high nibble
     .byte %00000001\
ORG FX20 ; second high nibble
     .byte %00000010
ORG FX30 ; third high nibble
     .byte %00000100
ORG FX40 ; fourth high nibble
     .byte %00001000

...

Hehe, cool! Now you can decode the high/low nibbles
ultra fast... :-)

Greetings,
     Manuel



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