3 ms·
Perhaps they meant to increment another variable and typed the label or address wrong (labels back then were generally much more limited in length on the averag
by LocalH 4y ago
Perhaps they meant to increment another variable and typed the label or address wrong (labels back then were generally much more limited in length on the average development system, I bet that the actual name for the variable in question was nowhere near the length of WarpZoneCtrl, most likely it was limited to 6 or 8 characters). I don't know the low level logic of the engine enough to know if there is a different variable that it would actually make sense to increment in this place.
- raldi 4y agoBased on the original leaked source code, it appears they really did intend to increment the variable they did. The comment matches the name and purpose: BEQ PLTMRT ; Scrool stopping ? ; : yes ! LDA PLYPS1 AND <PLYPS0 BNE PLTMRT ; Player Y pos = 0 ? ; STA SRSTFG ; yes ! INC CMSLFG ; Chimney select flag
- NobodyNada 4y agoThe 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!