tbkka 110e5136c1 Float16 optimal formatting (#30862) ...

Extend SwiftDtoa to provide optimal formatting for Float16 and use that for `Float16.description` and `Float16.debugDescription`.

Notes on signaling NaNs: LLVM's Float16 support passes Float16s on x86
by legalizing to Float32.  This works well for most purposes but incidentally
loses the signaling marker from any NaN (because it's a conversion as far
as the hardware is concerned), with a side effect that the print code never
actually sees a true sNaN.  This is similar to what happens with Float and
Double on i386 backends.  The earlier code here tried to detect sNaN in a
different way, but that approach isn't guaranteed to work so we decided to
make this code use the correct detection logic -- sNaN printing will just be
broken until we can get a better argument passing convention.

Resolves rdar://61414101

2020-04-09 09:37:38 -04:00

5.7 KiB

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