rjmccall added inline comments.
================ Comment at: clang/lib/Basic/FixedPoint.cpp:242 + } else + Overflowed = Result < Min || Result > Max; + ---------------- If the maximum expressible value is *k*, and the fully-precise multiplication yields *k+e* for some epsilon *e* that isn't representable in the result semantics, is that considered an overflow? If so, I think you need to do the shift after these bound checks, since the shift destroys the difference between *k* and *k+e*. That is, unless there's a compelling mathematical argument that it's not possible to overflow only in the fully-precision multiplication — but while I think that's possibly true of `_Fract` (since *k^2 < k*), it seems unlikely to be true of `_Accum`, although I haven't looked for a counter-example. And if there is a compelling argument, it should probably be at least alluded to in a comment. Would this algorithm be simpler if you took advantage of the fact that `APFixedPointSemantics` doesn't have to correspond to a real type? You could probably just convert to a double-width common semantics, right? Repository: rG LLVM Github Monorepo CHANGES SINCE LAST ACTION https://reviews.llvm.org/D73186/new/ https://reviews.llvm.org/D73186 _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
