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Re: [Qemu-devel] [PATCH] tcg/i386: fix unsigned vector saturating arithm

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH] tcg/i386: fix unsigned vector saturating arithmetic
Date: Fri, 8 Feb 2019 11:09:30 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

On 2/8/19 10:09 AM, Mark Cave-Ayland wrote:
> On 08/02/2019 17:39, Richard Henderson wrote:
>> On 2/7/19 2:42 PM, Mark Cave-Ayland wrote:
>>> Due to a cut/paste error in the original implementation, the unsigned vector
>>> saturating arithmetic was erroneously being calculated as signed vector 
>>> saturating
>>> arithmetic.
>>> Fixes: 8ffafbcec2 ("tcg/i386: Implement vector saturating arithmetic")
>>> Signed-off-by: Mark Cave-Ayland <address@hidden>
>>> ---
>>>  tcg/i386/tcg-target.inc.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> Ooof.  Thanks.
> AFAICT none of the other TCG backends currently make use of it, but it was 
> this bug
> causing the graphical corruption that myself and Howard saw testing the PPC 
> vector
> patchset.

I would have seen the error if I had done ARM SVE regression testing.
But I only did ARM NEON testing, which does not make use of this, and
I had forgotten that.

Like PPC, NEON sets a "saw saturation" bit.  I think I'll do the same
trick as we did for ppc to compute that with vector insns.

> FWIW I've now rebased and repushed the outstanding patches from your patchset 
> along
> with this fix to https://github.com/mcayland/qemu/commits/ppc-altivec-v6 as 
> it would
> be great if this could make it into 4.0.

I've given all of my r-b...


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