From: Richard Henderson <richard.henderson@linaro.org>
To: Paolo Bonzini <pbonzini@redhat.com>, qemu-devel@nongnu.org
Subject: Re: [PATCH] i386: DPPS rounding fix
Date: Thu, 25 Aug 2022 10:08:31 -0700 [thread overview]
Message-ID: <4c084547-cacd-585c-13c9-1f63ef9cc1f8@linaro.org> (raw)
In-Reply-To: <20220825164827.392942-1-pbonzini@redhat.com>
On 8/25/22 09:48, Paolo Bonzini wrote:
> The DPPS (Dot Product) instruction is defined to first sum pairs of
> intermediate results, then sum those values to get the final result.
> i.e. (A+B)+(C+D)
>
> We incrementally sum the results, i.e. ((A+B)+C)+D, which can result
> in incorrect rouding.
>
> For consistency, also change the variable names to the ones used
> in the Intel SDM and implement DPPD following the manual.
>
> Based on a patch by Paul Brook<paul@nowt.org>.
>
> Signed-off-by: Paolo Bonzini<pbonzini@redhat.com>
> ---
> target/i386/ops_sse.h | 67 ++++++++++++++++++++++---------------------
> 1 file changed, 35 insertions(+), 32 deletions(-)
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
r~
next prev parent reply other threads:[~2022-08-25 17:14 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-25 16:48 [PATCH] i386: DPPS rounding fix Paolo Bonzini
2022-08-25 17:08 ` Richard Henderson [this message]
-- strict thread matches above, loose matches on Subject: below --
2022-08-25 16:49 [PATCH] tests/i386: SSE tests Paolo Bonzini
2022-08-25 16:49 ` [PATCH] i386: DPPS rounding fix Paolo Bonzini
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