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From: "jsm28 at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug math/15421] New: lgamma wrongly sets signgam for ISO C
Date: Tue, 30 Apr 2013 16:42:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=15421

             Bug #: 15421
           Summary: lgamma wrongly sets signgam for ISO C
           Product: glibc
           Version: 2.17
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: jsm28@gcc.gnu.org
    Classification: Unclassified


The lgamma (and likewise lgammaf, lgammal) function wrongly sets the signgam
variable even when building for strict ISO C conformance (-std=c99 / -std=c11),
although the user may define such a variable and it's only in the
implementation namespace for POSIX with XSI extensions enabled.

In http://sourceware.org/ml/libc-alpha/2013-04/msg00767.html I describe a
possible approach for fixing this, involving new symbol versions so existing
binaries get existing setting of signgam while new binaries can be built for
ISO C semantics without necessarily including <math.h>, or can define
_XOPEN_SOURCE and include <math.h> to get setting of signgam.

(The versions in bits/math-finite.h use __USE_ISOC99 as the condition for
setting signgam, which is safe for ISO C but not correct for current POSIX with
XSI extensions enabled, which is based on C99 but should set signgam.)

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