Subject: Re: [stella] Arrrg, Arrrg, and Double Arrrg!!!|
From: Chris Wilkson <cwilkson@xxxxxxxxxxxxx>
Date: Wed, 15 Apr 1998 14:48:51 -0700 (PDT)
> How the heckety heck did you figure out that the branch wasn't being > taken after $7F? > > Changing the BPL to BNE fixed the problem, although I don't know why the > problem existed in the first place. I can't see what would make the > BLOW routine stop at $7F with a BPL in there, unless there is something > about the nature of BPL that I just don't understand. Doesn't it just > branch if the result is a positive number? BEQ branches if the result is > zero, BMI branches if the result is a negative number, and BNE branches if > the result is anything other than zero. Well, you're right. BPL does branch if the result is a positive number. But this is a BINARY positive/negative. Bit 7 is the sign bit: 0=pos 1=neg. (and $FF= -1, and $FE= -2, etc). And don't feel bad...I've got a good one along the same lines. I'll post it to the list later... -Chris -- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/stella.html Don't post pirate BINs to Stellalist. Be a programmer, not a pirate. Write the best game, win framed autographs of famous Atari alumni!!