From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <glibc-bugs-return-16885-listarch-glibc-bugs=sources.redhat.com@sourceware.org>
Received: (qmail 3981 invoked by alias); 29 Sep 2012 11:44:54 -0000
Received: (qmail 3919 invoked by uid 48); 29 Sep 2012 11:44:40 -0000
From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sources.redhat.com
Subject: [Bug math/14645] New: Incorrect sign of inexact zero result from fma
Date: Sat, 29 Sep 2012 11:44:00 -0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: glibc
X-Bugzilla-Component: math
X-Bugzilla-Keywords:
X-Bugzilla-Severity: normal
X-Bugzilla-Who: jsm28 at gcc dot gnu.org
X-Bugzilla-Status: NEW
X-Bugzilla-Priority: P2
X-Bugzilla-Assigned-To: unassigned at sourceware dot org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Changed-Fields:
Message-ID: <bug-14645-131@http.sourceware.org/bugzilla/>
X-Bugzilla-URL: http://sourceware.org/bugzilla/
Auto-Submitted: auto-generated
Content-Type: text/plain; charset="UTF-8"
MIME-Version: 1.0
Mailing-List: contact glibc-bugs-help@sourceware.org; run by ezmlm
Precedence: bulk
List-Id: <glibc-bugs.sourceware.org>
List-Subscribe: <mailto:glibc-bugs-subscribe@sourceware.org>
List-Post: <mailto:glibc-bugs@sourceware.org>
List-Help: <mailto:glibc-bugs-help@sourceware.org>, <http://sourceware.org/lists.html#faqs>
Sender: glibc-bugs-owner@sourceware.org
X-SW-Source: 2012-09/txt/msg00287.txt.bz2


http://sourceware.org/bugzilla/show_bug.cgi?id=14645

             Bug #: 14645
           Summary: Incorrect sign of inexact zero result from fma
           Product: glibc
           Version: 2.16
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: jsm28@gcc.gnu.org
    Classification: Unclassified


Various fma functions produce zero results with incorrect sign in the case
where the zero is (underflowing multiplication) + 0.  In such a case, IEEE
754-2008 (6.3 The sign bit) explicitly says "the zero result takes the sign of
the exact result".  But for example fmal (-LDBL_MIN, LDBL_MIN, 0.0L) wrongly
returns +0.0L instead of -0.0L on x86 because the implementation adds the -0.0L
from the multiplication to the +0.0L, so changing its sign to +0.0L (in
round-to-nearest mode).  This is the case even after my patch
http://sourceware.org/ml/libc-alpha/2012-09/msg00792.html for bug 14638 (signs
of *exact* zero results), which doesn't change the relevant code.

-- 
Configure bugmail: http://sourceware.org/bugzilla/userprefs.cgi?tab=email
------- You are receiving this mail because: -------
You are on the CC list for the bug.