Subject: Re: [stella] Programming tricks guide From: Memblers <jparsell317@xxxxxxxxxxx> Date: Sun, 09 Feb 2003 15:18:16 -0500 |
On 9 Feb 2003 at 15:35, KirkIsrael@xxxxxxxxxxxxx wrote: > What would be most helpful to me is something that covered some > basic things...for instance, I had trouble figuring out how to > do the equivalent of "comparison if then"--i.e. in pseudo code > > if X < Y then > do this > end if It sounds difficult, but it's actually quite simple once you understand how the CMP instruction works. An older program I made used to do a bunch of INCs or DECs with a compare to see which was greater. (that was _really_ slow and dumb, heheh) CMP is like the SBC instruction, the difference is that only the status flags are affected. In this case, you'll use the carry flag. LDA #20 CMP #10 BCC 20_is_greater_than_10 or.. LDA #10 CMP #20 BCS 10_is_less_than_20 See? CMP subtracts the given value from the accumulator, and sets the flags appropriately. I hope that helps. peace. Memblers http://www.parodius.com/~memblers/ ---------------------------------------------------------------------------------------------- Archives (includes files) at http://www.biglist.com/lists/stella/archives/ Unsub & more at http://www.biglist.com/lists/stella/
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