[libc-commits] [libc] [libc][math][c23] Add log10p1f16 C23 math function (PR #184739)

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zimmermann6 wrote:

assuming LLVM libc supports underflow after rounding, the spurious underflow is gone. However, I get a missing underflow:
```
zimmerma at croissant:~/svn/core-math$ CORE_MATH_CHECK_STD=true LIBM=$L ./check.sh log10p1f16
Running exhaustive check in --rndn mode...
all ok
Running exhaustive check in --rndz mode...
all ok
Running exhaustive check in --rndu mode...
Missing underflow exception for x=0x1.268p-13 (y=0x1p-14)
```
Indeed, the result is ```0x1.ff9....p-15```, which rounds upwards with full precision to ```0.x1ffcp-15```. Since this number is not representable, there is underflow.

https://github.com/llvm/llvm-project/pull/184739