[Bug math/6778] expm1() raises bogus underflow exception for -large

[Bug math/6778] expm1() raises bogus underflow exception for -large

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=6778

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|aj at suse dot de           |unassigned at sourceware
                   |                            |dot org

--- Comment #2 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-02-29 20:59:11 UTC ---
Confirmed on x86 with current sources.  Does not appear on x86_64.  This is a
quality-of-implementation issue only, since C99 and C11 permit spurious
underflow exceptions (as well as spurious inexact exceptions, and raising
inexact even when the result is exact).

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[Bug math/6778] expm1() raises bogus underflow exception for -large

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=6778

Joseph Myers <jsm28 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|                            |FIXED

--- Comment #3 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-07-06 11:19:45 UTC ---
Fixed for 2.17 by:

commit f17ac40d7cb8e8c462476b6ab703262f6b8f6da8
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Fri Jul 6 11:17:41 2012 +0000

    Fix expm1 spurious underflow exceptions (bug 6778).

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[Bug math/6778] expm1() raises bogus underflow exception for -large

[mtk.manpages at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=6778

--- Comment #4 from Michael Kerrisk <mtk.manpages at gmail dot com> ---
Fix documented for man-pages-5.07.

commit 4f16aab8244518d9f46fb6e8d4dc8e6e73266771
Author: Michael Kerrisk <mtk.manpages@gmail.com>
Date:   Sat May 23 11:45:36 2020 +0200

    expm1.3: The expm1() bogus underflow floating-point exception has been
fixed

    Fixed in glibc 2.17.

    See https://www.sourceware.org/bugzilla/show_bug.cgi?id=6778

    Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man3/expm1.3 b/man3/expm1.3
index a1fe0f7b2..460068a6d 100644
--- a/man3/expm1.3
+++ b/man3/expm1.3
@@ -144,13 +144,14 @@ T}        Thread safety   MT-Safe
 C99, POSIX.1-2001, POSIX.1-2008.
 .\" BSD.
 .SH BUGS
-For some large negative
+Before glibc 2.17,
+.\" http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
+on certain architectures (e.g., x86, but not x86_64)
+.BR expm1 ()
+raised a bogus underflow floating-point exception
+for some large negative
 .I x
 values (where the function result approaches \-1),
-.BR expm1 ()
-raises a bogus underflow floating-point exception.
-.\" FIXME .
-.\" Bug raised: http://sources.redhat.com/bugzilla/show_bug.cgi?id=6778
 .PP
 For some large positive
 .I x

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[Bug math/6778] New: expm1() raises bogus underflow exception for -large

[mtk dot manpages at gmail dot com]

(glibc 2.8)
When expm1(x) is given a large negative x value (e.g., in the range -1e5 through
to -1e308), it correctly returns -1.

However, it also raises an underflow exception.  This is bogus.  The result has
not underflowed: the result is asymptotically close to 1 (not zero).

-- 
           Summary: expm1() raises bogus underflow exception for -large
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: aj at suse dot de
        ReportedBy: mtk dot manpages at gmail dot com
                CC: glibc-bugs at sources dot redhat dot com


http://sourceware.org/bugzilla/show_bug.cgi?id=6778

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[Bug math/6778] expm1() raises bogus underflow exception for -large

[mtk dot manpages at gmail dot com]

------- Additional Comments From mtk dot manpages at gmail dot com  2008-07-31 08:29 -------
Created an attachment (id=2843)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=2843&action=view)
test program

Example runs showing problem:

$ /tmp/mt_expm1 -- -1e5
errno == 0
fetestexcept() says:  FE_UNDERFLOW FE_INEXACT
expm1(-1.00000000000000000e+05)=-1.00000000000000000e+00
0 FE_UNDERFLOW normal

$ /tmp/mt_expm1 -- -1e308
errno == 0
fetestexcept() says:  FE_UNDERFLOW FE_INEXACT
expm1(-1.00000000000000001e+308)=-1.00000000000000000e+00
0 FE_UNDERFLOW normal


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