From: Michael Matz <matz@suse.de>
To: Joseph Myers <joseph@codesourcery.com>
Cc: James Greenhalgh <james.greenhalgh@arm.com>,
"pinskia@gmail.com" <pinskia@gmail.com>,
"gcc-patches@gcc.gnu.org" <gcc-patches@gcc.gnu.org>
Subject: Re: [Patch match.pd] Add a simplify rule for x * copysign (1.0, y);
Date: Thu, 01 Oct 2015 16:15:00 -0000 [thread overview]
Message-ID: <alpine.LSU.2.20.1510011809420.1349@wotan.suse.de> (raw)
In-Reply-To: <alpine.DEB.2.10.1510011555060.25019@digraph.polyomino.org.uk>
Hi,
On Thu, 1 Oct 2015, Joseph Myers wrote:
> On Thu, 1 Oct 2015, Michael Matz wrote:
>
> > both cases. The catch is that strictly speaking (NaN * -1.0) needs to
> > deliver NaN, not -NaN (operations involving quiet NaNs need to provide
> > one of the input NaNs as result), and here both are not equivalent. OTOH
> > the sign of NaNs isn't specified, so I think we could reasonably decide to
> > not care about this case (it would have to be checked if the hardware
> > multiplication even follows that rule, otherwise it's moot anyway).
>
> "For all other operations, this standard does not specify the sign bit of
> a NaN result, even when there is only one input NaN, or when the NaN is
> produced from an invalid operation." (IEEE 754-2008, 6.3 The sign bit).
> So no need to care about this case.
Ah. I was looking at an old version; thanks.
Ciao,
Michael.
next prev parent reply other threads:[~2015-10-01 16:15 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-01 13:57 James Greenhalgh
2015-10-01 14:28 ` pinskia
2015-10-01 14:51 ` James Greenhalgh
2015-10-01 15:03 ` pinskia
2015-10-01 15:43 ` Michael Matz
2015-10-01 15:49 ` Jakub Jelinek
2015-10-01 16:09 ` Michael Matz
2015-10-01 15:59 ` Joseph Myers
2015-10-01 16:15 ` Michael Matz [this message]
2015-10-01 18:36 ` Jakub Jelinek
2015-10-02 8:18 ` Richard Biener
2015-10-02 9:04 ` Jakub Jelinek
2015-10-02 9:11 ` Richard Biener
2015-10-02 9:27 ` Jakub Jelinek
2015-10-02 9:45 ` Richard Biener
2015-10-02 9:58 ` Jakub Jelinek
2015-10-02 10:07 ` Marek Polacek
2015-10-02 10:24 ` James Greenhalgh
2015-10-02 10:29 ` Marek Polacek
2015-10-02 10:32 ` Richard Biener
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