Re: [stella] Starmaster disassembled

Subject: Re: [stella] Starmaster disassembled
From: "Thomas Jentzsch" <tjentzsch@xxxxxx>
Date: Thu, 2 Aug 2001 11:48:09 +0200
Glenn Saunders wrote:
> >>
> This was not the first game for the 2600 Alan wrote, so maybe somebody else
> started or was involved into the project.

Yes, that could be, or he reused old code from other of his games. I have to look at Checkers, there could be a similar encoding code.

> <<
> Al invented playfield bitmaps in Surround.  That's no easy feat.  Take a 
> look at Surround and see if there are any LSRs.  I find it hard to believe 
> that he didn't know the entire 6502 instruction set by the time Starmaster 
> was coded

I had a look at disassembled Surround code, look what i found (there are several similar parts):

       LDA    $F6     ;3
       AND    #$F0    ;2
       LSR    A       ;2
       LSR    A       ;2
       LSR    A       ;2
       LSR    A       ;2
       TAY            ;2
       LDA    LF78F,Y ;4
       CLC            ;2
       ADC    LF799,X ;4

He is masking out the lower 4 bits with AND #$F0 and(!) later he is clearing the carry. It's unneccessary to do both, he should have chosen CLC, because it's uses only 1 byte. 

To me it looks, like he sometimes(?) had some problems with shifting to the right :)

> Starmaster is 4K or 8K?  I could understand having some "slop" in an 8K game 
> if there was plenty of room to spare and if the programmer was trying to 
> crank out product.  David Crane was especially prolific.  Al Miller less so, 
> but also no slouch.

It's only 4K, with some size optimizations like overlapping tables etc. He definitely was short of ROM space.

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

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