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From: Nikunj Dadhania <nikunj.dadhania@gmail.com>
To: Richard Henderson <rth@twiddle.net>
Cc: qemu-devel@nongnu.org, qemu-ppc@nongnu.org,
	Nikunj A Dadhania <nikunj@linux.vnet.ibm.com>,
	David Gibson <david@gibson.dropbear.id.au>,
	bharata@linux.vnet.ibm.com
Subject: Re: [Qemu-devel] [Qemu-ppc] [PATCH v1] target/ppc: rewrite f[n]m[add, sub] using float64_muladd
Date: Thu, 2 Mar 2017 09:38:14 +0530	[thread overview]
Message-ID: <CALAZu3_e8AWbOpASxY9s97AyNd+CX=BYCMx3g4KrG2Ki6w1CZg@mail.gmail.com> (raw)
In-Reply-To: <32926f1f-ec40-420f-210b-8f5991cc9d67@twiddle.net>

On 02-Mar-2017 7:53 AM, "Richard Henderson" <rth@twiddle.net> wrote:

On 03/02/2017 11:29 AM, David Gibson wrote:

> On Wed, Mar 01, 2017 at 08:54:14PM +0530, Nikunj A Dadhania wrote:
>
>> Use the softfloat api for fused multiply-add. Also, generate VXISI using
>> a helper function by computing intermediate result.
>>
>
> Um.. I really need some information on why this is a good thing to
> do.  Is it a bugfix?  Enhancement? Simplification?
>

Looks like a bugfix to me.  Previously we were attempting the operation via
float128 as an intermediate type, which can result in double rounding
errors.

Was discussed here

https://lists.gnu.org/archive/html/qemu-devel/2016-10/msg02000.html

Nikunj

  reply	other threads:[~2017-03-02  4:08 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-01 15:24 [Qemu-devel] [PATCH v1] target/ppc: rewrite f[n]m[add, sub] using float64_muladd Nikunj A Dadhania
2017-03-02  0:29 ` David Gibson
2017-03-02  2:22   ` Richard Henderson
2017-03-02  4:08     ` Nikunj Dadhania [this message]
2017-03-02  5:03       ` [Qemu-devel] [Qemu-ppc] " Nikunj A Dadhania
2017-03-02  2:36 ` [Qemu-devel] " Richard Henderson
2017-03-02  4:14   ` [Qemu-devel] [Qemu-ppc] " Nikunj Dadhania
2017-03-02  5:04     ` Nikunj A Dadhania

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