scanon added inline comments.
================
Comment at: lib/Sema/SemaChecking.cpp:110
+/// are usually useless
+static unsigned AdjustPrecision(unsigned precision) {
+ return (precision * 59 + 195) / 196;
----------------
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.
https://reviews.llvm.org/D52835
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