From: Joseph Myers <joseph@codesourcery.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-devel@nongnu.org, ehabkost@redhat.com, rth@twiddle.net
Subject: Re: [PATCH v2] target/i386: reimplement fpatan using floatx80 operations
Date: Tue, 23 Jun 2020 14:23:13 +0000 [thread overview]
Message-ID: <alpine.DEB.2.21.2006231411570.29757@digraph.polyomino.org.uk> (raw)
In-Reply-To: <27588539-95cc-f10f-b8c2-c263b56c921a@redhat.com>
On Tue, 23 Jun 2020, Paolo Bonzini wrote:
> On 23/06/20 02:01, Joseph Myers wrote:
> > The x87 fpatan emulation is currently based around conversion to
> > double. This is inherently unsuitable for a good emulation of any
> > floatx80 operation. Reimplement using the soft-float operations, as
> > for other such instructions.
> >
> > Signed-off-by: Joseph Myers <joseph@codesourcery.com>
>
> Queued, thanks.
>
> Just one question: do recent processors still use the same CORDIC
> approximations as the 8087, and if so would it be better or simpler to
> do that instead of using a good implementation such as this one?
I don't know what approximations the processors use, but they're
definitely different for at least some instructions between Intel and AMD
processors (as shown by glibc test ulps baselines created on one processor
sometimes needing increasing to work on other processors; avoiding test
problems means the emulation needs to be at least as accurate as
hardware). (Whereas the AVX-512 approximation instructions have reference
implementations for their exact semantics.)
--
Joseph S. Myers
joseph@codesourcery.com
next prev parent reply other threads:[~2020-06-23 14:24 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 0:01 [PATCH v2] target/i386: reimplement fpatan using floatx80 operations Joseph Myers
2020-06-23 0:31 ` Paolo Bonzini
2020-06-23 0:33 ` Paolo Bonzini
2020-06-23 14:23 ` Joseph Myers [this message]
2020-06-23 1:32 ` no-reply
2020-06-23 1:33 ` no-reply
2020-06-23 1:35 ` no-reply
2020-06-23 1:39 ` no-reply
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