Bug 828980 - glibc libm regression: 0^-inf is -inf instead of +inf
glibc libm regression: 0^-inf is -inf instead of +inf
Product: Fedora
Classification: Fedora
Component: glibc (Show other bugs)
x86_64 Linux
unspecified Severity high
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Assigned To: Jeff Law
Fedora Extras Quality Assurance
Depends On:
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Reported: 2012-06-05 13:14 EDT by Michel Alexandre Salim
Modified: 2016-11-24 11:13 EST (History)
6 users (show)

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Fixed In Version:
Doc Type: Bug Fix
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Last Closed: 2012-06-14 14:54:29 EDT
Type: Bug
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Attachments (Terms of Use)
Test case reproducing the regression (216 bytes, application/octet-stream)
2012-06-05 13:14 EDT, Michel Alexandre Salim
no flags Details

External Trackers
Tracker ID Priority Status Summary Last Updated
Sourceware 14241 None None None Never

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Description Michel Alexandre Salim 2012-06-05 13:14:05 EDT
Created attachment 589588 [details]
Test case reproducing the regression

Description of problem:
ISO/IEC 9899:TC3, Annex F.9.4.4 specifies that pow(0, -INFINITY) is inf, as it is in F-17's glibc-2.15-37.fc17.x86_64; however, in Rawhide's glibc, the same calculation returns -inf -- as tested by compiling the attached test case (either on F-17 or Rawhide) and running it with one glibc or the other.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. glibc -lm -o powtest powtest.c
Actual results:
pow(0.0, -INFINITY) = -inf (positive? 0)

Expected results:
pow(0.0, -INFINITY) = inf (positive? 1)

Additional info:
Noticed during a rebuild of Pure; test case provided by Pure author:
Comment 1 Michel Alexandre Salim 2012-06-05 13:14:54 EDT
(In reply to comment #0)
> Steps to Reproduce:
> 1. glibc -lm -o powtest powtest.c
That should be gcc -lm -o powtest powtest.c, of course.
Comment 2 Jeff Law 2012-06-14 14:48:40 EDT
This is due to this upstream patch:

commit 2460d3aa21f04cdf28497683bd3e29183189f779
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Mar 21 12:14:57 2012 +0000

    Fix pow of zero and infinity to large powers.
Comment 3 Jeff Law 2012-06-14 14:54:29 EDT
I'm going to let Joseph handle it upstream.  We'll pick up the fix via our normal merging processes.
Comment 4 Jeff Law 2012-06-15 11:24:31 EDT
BTW, Joseph checked in a fix upstream and I've resyncd Rawhide with the upstream sources.
Comment 5 Michel Alexandre Salim 2012-06-16 00:34:56 EDT
Could you update the bug tracker once there's a build on Koji I can test? The latest build is from June 13th and predates this fix. Thanks!
Comment 6 Jeff Law 2012-06-18 13:35:35 EDT
Just spun a fawhide build this morning which should contain this fix.
Comment 7 Michel Alexandre Salim 2012-06-19 07:22:51 EDT
Confirmed that the failing test case in pure that originally revealed this bug now passes.

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