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* [Bug math/14645] New: Incorrect sign of inexact zero result from fma
@ 2012-09-29 11:44 jsm28 at gcc dot gnu.org
2012-10-01 8:32 ` [Bug math/14645] " jsm28 at gcc dot gnu.org
2014-06-17 4:13 ` fweimer at redhat dot com
0 siblings, 2 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-09-29 11:44 UTC (permalink / raw)
To: glibc-bugs
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.
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* [Bug math/14645] Incorrect sign of inexact zero result from fma
2012-09-29 11:44 [Bug math/14645] New: Incorrect sign of inexact zero result from fma jsm28 at gcc dot gnu.org
@ 2012-10-01 8:32 ` jsm28 at gcc dot gnu.org
2014-06-17 4:13 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-10-01 8:32 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14645
Joseph Myers <jsm28 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
--- Comment #1 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-10-01 08:32:37 UTC ---
Fixed by:
commit bec749fda1cbc1934f7e58dd2763603f4f207f26
Author: Joseph Myers <joseph@codesourcery.com>
Date: Mon Oct 1 08:30:06 2012 +0000
Fix sign of inexact zero return from fma (bug 14645).
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* [Bug math/14645] Incorrect sign of inexact zero result from fma
2012-09-29 11:44 [Bug math/14645] New: Incorrect sign of inexact zero result from fma jsm28 at gcc dot gnu.org
2012-10-01 8:32 ` [Bug math/14645] " jsm28 at gcc dot gnu.org
@ 2014-06-17 4:13 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: fweimer at redhat dot com @ 2014-06-17 4:13 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=14645
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2012-09-29 11:44 [Bug math/14645] New: Incorrect sign of inexact zero result from fma jsm28 at gcc dot gnu.org
2012-10-01 8:32 ` [Bug math/14645] " jsm28 at gcc dot gnu.org
2014-06-17 4:13 ` fweimer at redhat dot com
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