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

[Eric Bresie]

Not directly related (and as I’m not really an expert on these things, nor able to change in any way) but was looking at the code mentioned and saw line like:

if (x == 0.0 || y == 0.0)

return (x * y + z);

If either x or y is zero would it be better to just return z and avoid an extra multiplication operation here?
Eric Bresie
Ebresie@gmail.com

> On September 2, 2020 at 12:59:43 PM CDT, Sebastian Huber <sebastian.huber@embedded-brains.de> wrote:
> On 02/09/2020 19:12, Joseph Myers wrote:
>
> > On Wed, 2 Sep 2020, Sebastian Huber wrote:
> >
> > > https://sourceware.org/git/?p=glibc.git;a=blob;f=math/s_fma.c;h=4d73af4f65d511594b2395d032a135721c578484;hb=HEAD
> > No glibc configurations use that; they all use either a hardware
> > instruction, an implementation based on sticky rounding as described by
> > Boldo and Melquiond, or, in the absence of hardware exceptions and
> > rounding modes, a soft-fp implementation.
>
> Sorry for pointing to this dead code in glibc.
>
> Maybe we can use the FreeBSD implementation:
>
> https://github.com/freebsd/freebsd/blob/master/lib/msun/src/s_fma.c
>
> It is probably also used by Bionic:
>
> https://android.googlesource.com/platform/bionic/+/refs/heads/master/libm/upstream-freebsd/lib/msun/src/s_fma.c
>