Home/Envision/Memorabilia/Evil Bug

This page shows the DEY/BPL bug that had me tearing my hair out for almost two months (off and on). I very nearly abandoned the project altogether because of it. Then I learned about two's-complement signed arithmetic and saw the error of my ways.
The bug (indicated by the two red dots) occurs because the maximum number of columns (MAXCOLS) can be greater than 127, in which case the code flow just falls right out of the blasted loop.

Evil bug

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