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* [Bug math/14783] New: Incorrect subnormal fma results in non-default rounding modes
@ 2012-10-29 23:56 jsm28 at gcc dot gnu.org
2012-10-30 13:57 ` [Bug math/14783] " jsm28 at gcc dot gnu.org
2014-06-14 11:17 ` fweimer at redhat dot com
0 siblings, 2 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-10-29 23:56 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14783
Bug #: 14783
Summary: Incorrect subnormal fma results in non-default
rounding modes
Product: glibc
Version: 2.16
Status: NEW
Severity: normal
Priority: P2
Component: math
AssignedTo: unassigned@sourceware.org
ReportedBy: jsm28@gcc.gnu.org
Classification: Unclassified
The various fma implementations have logic for scaling down results, in the
case of subnormal results that are at least half the smallest positive normal
value in magnitude, that assumes round-to-nearest and so is incorrect in other
rounding modes. (The code at fault is the same as in bug 14152, but from the
user perspective they are separate bugs, missing exceptions (any rounding mode)
versus incorrect results (non-default rounding modes).)
For example, on x86, fmal (0x1.4p-16382L, 0x1.0000000000000004p-1L,
0x1p-16384L) returns 0x7.000000000000001p-16385L independent of rounding mode,
but this should be 0x7.000000000000002p-16385L in FE_UPWARD mode.
Working on a patch.
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* [Bug math/14783] Incorrect subnormal fma results in non-default rounding modes
2012-10-29 23:56 [Bug math/14783] New: Incorrect subnormal fma results in non-default rounding modes jsm28 at gcc dot gnu.org
@ 2012-10-30 13:57 ` jsm28 at gcc dot gnu.org
2014-06-14 11:17 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-10-30 13:57 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14783
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> 2012-10-30 13:56:59 UTC ---
Fixed for 2.17 by:
commit 8627a2329c5e6fc09bf9f0f070a21aca41f2b122
Author: Joseph Myers <joseph@codesourcery.com>
Date: Tue Oct 30 13:54:50 2012 +0000
Fix fma missing underflows and bad results for some subnormal results (bugs
14152, 14783).
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* [Bug math/14783] Incorrect subnormal fma results in non-default rounding modes
2012-10-29 23:56 [Bug math/14783] New: Incorrect subnormal fma results in non-default rounding modes jsm28 at gcc dot gnu.org
2012-10-30 13:57 ` [Bug math/14783] " jsm28 at gcc dot gnu.org
@ 2014-06-14 11:17 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: fweimer at redhat dot com @ 2014-06-14 11:17 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=14783
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2012-10-29 23:56 [Bug math/14783] New: Incorrect subnormal fma results in non-default rounding modes jsm28 at gcc dot gnu.org
2012-10-30 13:57 ` [Bug math/14783] " jsm28 at gcc dot gnu.org
2014-06-14 11:17 ` fweimer at redhat dot com
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