Re: [stella] Bit flip

Subject: Re: [stella] Bit flip
From: Glenn Saunders <cybpunks2@xxxxxxxxxxxxx>
Date: Mon, 10 Sep 2001 01:51:08 -0700
At 06:36 PM 9/10/2001 +1000, you wrote:
Table-lookup, 256 bytes. Index your original value to get the bit-flipped

It wouldn't need 256 bytes because if only 1 bit is set then there can only be 8 possible values:


Would need to index a table containing:


But how do you use a number like that to create an index?

Would you left shift the accumulator and test for zero and increment the X register until it reaches zero, then LDA Lookup,X?

To be more specific, I'm starting to think (getting ahead of myself, before I even have a working kernel) of how to translate an X/Y coordinate of a collision into a playfield bitmap RAM write. Because the playfield registers are stored in alternating normal and reversed bit order I can't just write directly. I need to potentially reverse the bit order before I OR it with the proper RAM location.

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