[PATCH] D52835: [Diagnostics] Check integer to floating point number implicit conversions

[Craig Topper via Phabricator via cfe-commits]

craig.topper added inline comments.


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Comment at: lib/Sema/SemaChecking.cpp:110
+/// are usually useless
+static unsigned AdjustPrecision(unsigned precision) {
+  return (precision * 59 + 195) / 196;
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scanon wrote:
> erichkeane wrote:
> > Hmm.... I don't terribly understand how this function works.  Also, comment above needs to end in a period.  
> > 
> > Can you elaborate further as to how this works?  Those are 3 pretty suspect looking magic numbers...
> It's attempting to compute the number of good base-10 digits (59/196 ~= log2(10)). We should really just make APFloat print the shortest round-trippable digit sequence instead. Yes, this is tricky to implement, but we don't need to implement it. There are two recent high-quality implementations available, which are both significantly faster than previous algorithms: Ryu and Swift's (https://github.com/apple/swift/blob/master/stdlib/public/runtime/SwiftDtoa.cpp). Swift's has the virtue of already being used in LLVM-family languages and having a tidy single-file implementation, but either would be perfectly usable, I think.
> 
> Neither supports float128 yet, but we could simply drop them in for float, double, and float80.
Function names should start with lower case I think?


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Comment at: lib/Sema/SemaChecking.cpp:111
+static unsigned AdjustPrecision(unsigned precision) {
+  return (precision * 59 + 195) / 196;
+}
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Can we use divideCeil from llvm/Support/MathExtras.h?


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Comment at: lib/Sema/SemaChecking.cpp:10881
+          SmallString<16> PrettySourceValue;
+          unsigned precision = llvm::APFloat::semanticsPrecision(*FloatSem);
+          precision = AdjustPrecision(precision);
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Variable name should start with uppercase


https://reviews.llvm.org/D52835