4 ms·
The buggy AND is really interesting to me -- the comment suggests that maybe the programmer meant to use an ORA instead, which would have been a clever way to c
by NobodyNada 4y ago
The buggy AND is really interesting to me -- the comment suggests that maybe the programmer meant to use an ORA instead, which would have been a clever way to check if both bytes of the Y position were zero. But that's still not something that makes sense to check, right? Assuming I'm understanding the video right, that'd only unlock the scroll if Mario was way up above the top of the screen...
- raldi 4y agoI believe the NES's 6502 didn't have a logical-OR operator (which is what the situation calls for), only bitwise. The apparent goal was to find out, "Are either PLYPS0 or PLYPS1 equal to 0?" They probably started with ORA, and when that didn't work, tried AND, and that seemed to work, so they went with it.
- NobodyNada 4y agoOhhh, that makes sense. Thanks!