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* [Bug math/14797] New: fma use of a * b + c on overflow incorrect in directed rounding modes
@ 2012-11-01 23:47 jsm28 at gcc dot gnu.org
2012-11-04 19:27 ` [Bug math/14797] " jsm28 at gcc dot gnu.org
2014-06-14 11:16 ` fweimer at redhat dot com
0 siblings, 2 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-11-01 23:47 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14797
Bug #: 14797
Summary: fma use of a * b + c on overflow incorrect in directed
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
Various fma implementations fall back to a * b + c when a * b is known to
overflow so much that the final result would still overflow, whatever the value
of c. But this is incorrect in directed rounding modes where a * b may not be
an infinity. Example using dbl-64/s_fma.c: fma (DBL_MAX, DBL_MAX, -DBL_MIN)
should return DBL_MAX in FE_DOWNWARD mode but returns the next smaller
floating-point number instead.
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* [Bug math/14797] fma use of a * b + c on overflow incorrect in directed rounding modes
2012-11-01 23:47 [Bug math/14797] New: fma use of a * b + c on overflow incorrect in directed rounding modes jsm28 at gcc dot gnu.org
@ 2012-11-04 19:27 ` jsm28 at gcc dot gnu.org
2014-06-14 11:16 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-11-04 19:27 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=14797
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> 2012-11-04 19:27:07 UTC ---
Fixed for 2.17 by:
commit a0c2940d67e59b2f19515e2ac7280a7be9629ffa
Author: Joseph Myers <joseph@codesourcery.com>
Date: Sun Nov 4 19:26:02 2012 +0000
Fix fma overflow results outside round-to-nearest mode (bug 14797).
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* [Bug math/14797] fma use of a * b + c on overflow incorrect in directed rounding modes
2012-11-01 23:47 [Bug math/14797] New: fma use of a * b + c on overflow incorrect in directed rounding modes jsm28 at gcc dot gnu.org
2012-11-04 19:27 ` [Bug math/14797] " jsm28 at gcc dot gnu.org
@ 2014-06-14 11:16 ` fweimer at redhat dot com
1 sibling, 0 replies; 3+ messages in thread
From: fweimer at redhat dot com @ 2014-06-14 11:16 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=14797
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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2012-11-01 23:47 [Bug math/14797] New: fma use of a * b + c on overflow incorrect in directed rounding modes jsm28 at gcc dot gnu.org
2012-11-04 19:27 ` [Bug math/14797] " jsm28 at gcc dot gnu.org
2014-06-14 11:16 ` fweimer at redhat dot com
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