From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: Keith Packard <keithp@keithp.com>, newlib@sourceware.org
Subject: Re: [PATCH 0/3] ARM with only 32-bit floats do not have fast 64-bit FMA
Date: Mon, 10 Aug 2020 15:43:16 +0100 [thread overview]
Message-ID: <20200810144316.GM14398@arm.com> (raw)
In-Reply-To: <20200810093057.GD53219@calimero.vinschen.de>
The 08/10/2020 11:30, Corinna Vinschen wrote:
> Hi Szabolcs,
>
> ok to push?
>
this looks ok.
i would have used the arm specific macros
( __ARM_FEATURE_FMA, __ARM_FP) directly
in arm specific code.
but using HAVE_FAST_FMA{F} works too.
(note that these macros currently only
do something useful on aarch64 and arm.)
>
> 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
>
--
next prev parent reply other threads:[~2020-08-10 14:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-08 22:34 Keith Packard
2020-08-08 22:34 ` [PATCH 1/3] libm: ARM without HW double does not have fast FMA Keith Packard
2020-08-08 22:34 ` [PATCH 2/3] libm: Detect fast fmaf support Keith Packard
2020-08-08 22:34 ` [PATCH 3/3] libm/machine/arm: Add optimized fmaf and fma when available Keith Packard
2020-08-10 9:30 ` [PATCH 0/3] ARM with only 32-bit floats do not have fast 64-bit FMA Corinna Vinschen
2020-08-10 14:43 ` Szabolcs Nagy [this message]
2020-08-10 15:19 ` Keith Packard
2020-08-10 19:06 ` Corinna Vinschen
2020-09-01 16:32 ` Sebastian Huber
2020-09-01 17:21 ` Sebastian Huber
2020-09-01 18:04 ` Sebastian Huber
2020-09-01 19:28 ` Keith Packard
2020-09-01 21:16 ` Joseph Myers
2020-09-01 23:06 ` Keith Packard
2020-09-02 4:41 ` Sebastian Huber
2020-09-02 5:25 ` Keith Packard
2020-09-02 5:35 ` Keith Packard
2020-09-02 17:12 ` Joseph Myers
2020-09-02 17:59 ` Sebastian Huber
2020-09-02 20:39 ` Keith Packard
2020-09-01 19:50 ` Keith Packard
2020-09-07 14:09 Eric Bresie
2020-09-07 17:16 ` Keith Packard
2020-09-07 20:16 ` Brian Inglis
2020-09-07 22:23 ` Keith Packard
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