Re: use of fma

[Tulio Magno Quites Machado Filho <tuliom@ascii.art.br>]

Paul Zimmermann <Paul.Zimmermann@inria.fr> writes:

>> Side note: single and double-precision multiply-add have been available since
>> the PPC ISA and POWER1 ISA respectively.
>> So, they're also available by default on powerpc64 and powerpc builds
>> supporting hw fpu.
>
> thank you Tulio Magno. By the way, does anyone know of any hardware with
> extended double and/or quadruple precision multiply-add?

That's a good example of FMA that is not available by default on any of the
ABIs because it has been added to the POWER ISA 3.0 (e.g. POWER9).  :-D

You need a new enough compiler (GCC >= 7.4), but you can use gcc135 (POWER9)
from the GCC Compile Farm project:

[tuliom@gcc135 ~]$ /opt/at12.0/bin/gcc -O2 -mcpu=power9 -g -dM -E -xc /dev/null | grep __FP_FAST_FMA
#define __FP_FAST_FMAF128 1
#define __FP_FAST_FMAF 1
#define __FP_FAST_FMAF64x 1
#define __FP_FAST_FMAF32 1
#define __FP_FAST_FMAF64 1
#define __FP_FAST_FMAF32x 1
#define __FP_FAST_FMA 1

Notice I used -mcpu instead of -march.

-- 
Tulio Magno