Yeah, my code is dirty in many aspects, not warning-free and not 64-bit compatible. I warned JD about that. Negative array indices are allowed by C (C 99 standard, 126.96.36.199, 188.8.131.52), provided that an array is effectively a pointer into another array, which is the case here. It's a dangerous programming practice, though. leftup and the likes should be signed, as I suggested on the previous page. In r6390 JD made them unsigned, it may be (just a guess) a cause for crashes on 64 bit machines. One option is to exclude VI filters entirely until the clean implementation is written. Another option is to roll back altogether and then add functionality from my code in parts.