[PATCH 0/3] ARM with only 32-bit floats do not have fast 64-bit FMA

[Corinna Vinschen]

Hi Szabolcs,

ok to push?


Thanks,
Corinna

On Aug  8 15:34, Keith Packard via Newlib wrote:
> I added some new test configurations to my CI system for picolibc and
> discovered that when the new math code was built on 32-bit ARM
> processors with only single-precision floating hardware, several math
> functions were returning imprecise results. I got the expected results
> on processors with no FPU and on processors with both 32- and 64- bit
> FPUs.
> 
> I discovered that the affected functions were using the 'fma' function
> on this hardware, even though (lacking 64-bit HW support), that
> function was being emulated without the required precision.
> 
> This all boiled down to math_config.h incorrectly detecting 64-bit FMA
> support on ARM processors.
> 
> This patch series contains three changes:
> 
>  1. fix the fast FMA process so that 32-bit ARM processors without 64-bit FMA
>     support don't use 'fma' for the new math functions
> 
>  2. Add detection of fast FMAF, which 32-bit ARM processors with only
>     32-bit FPUs *do* support.
> 
>  3. Add ARM versions of fma and fmaf which are used when those
>     instructions are available.
> 

-- 
Corinna Vinschen
Cygwin Maintainer
Red Hat