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[Bug math/18371] csqrt spurious underflows
- From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sourceware dot org
- Date: Tue, 23 Jun 2015 16:02:51 +0000
- Subject: [Bug math/18371] csqrt spurious underflows
- Auto-submitted: auto-generated
- References: <bug-18371-131 at http dot sourceware dot org/bugzilla/>
https://sourceware.org/bugzilla/show_bug.cgi?id=18371
--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
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The branch, master has been updated
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from b59549574efeeecf124de05c9183c120eaaa56f0 (commit)
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- Log -----------------------------------------------------------------
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=718d34a309493f8697ff9a8fefcbacbba12a2ccd
commit 718d34a309493f8697ff9a8fefcbacbba12a2ccd
Author: Joseph Myers <joseph@codesourcery.com>
Date: Tue Jun 23 16:01:54 2015 +0000
Fix csqrt spurious underflows (bug 18371).
The csqrt implementations in glibc can cause spurious underflows in
some cases as a side-effect of the scaling for large arguments (when
underflow is correct for the square root of the argument that was
scaled down to avoid overflow, but not for the original argument).
This patch arranges to avoid the underflowing intermediate computation
(eliminating a multiplication in 0.5 in the problem cases where a
subsequent scaling by 2 would follow).
Tested for x86_64 and x86 and ulps updated accordingly (only needed
for x86).
[BZ #18371]
* math/s_csqrt.c (__csqrt): Avoid multiplication by 0.5 where
intermediate but not final result might underflow.
* math/s_csqrtf.c (__csqrtf): Likewise.
* math/s_csqrtl.c (__csqrtl): Likewise.
* math/auto-libm-test-in: Add more tests of csqrt.
* math/auto-libm-test-out: Regenerated.
* sysdeps/i386/fpu/libm-test-ulps: Update.
-----------------------------------------------------------------------
Summary of changes:
ChangeLog | 9 +
NEWS | 10 +-
math/auto-libm-test-in | 7 +
math/auto-libm-test-out | 766 +++++++++++++++++++++++++++++++++++++++
math/s_csqrt.c | 20 +-
math/s_csqrtf.c | 20 +-
math/s_csqrtl.c | 20 +-
sysdeps/i386/fpu/libm-test-ulps | 2 +
8 files changed, 843 insertions(+), 11 deletions(-)
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