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* [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234
@ 2008-02-26 7:04 petrosyan at gmail dot com
2008-02-26 7:09 ` [Bug math/5794] " petrosyan at gmail dot com
` (3 more replies)
0 siblings, 4 replies; 7+ messages in thread
From: petrosyan at gmail dot com @ 2008-02-26 7:04 UTC (permalink / raw)
To: glibc-bugs
The value of (e^x - 1) is representable as a long double when x <=
11356.5234, but expm1l(x) overflows to infinity when x > 11356.1768
(approximately).
Steps to Reproduce:
Compile and run the following program:
#include <stdio.h>
#include <math.h>
main ()
{
long double a, b;
const long double x = 11356.35L;
a = expl (x) - 1.0L;
b = expm1l (x);
if (a == b) {
printf ("e^%.2Lf - 1 = %Lg\n", b);
return 0;
} else {
printf ("e^%.2Lf - 1 = %Lg; but expm1l(%.2Lf) returned %Lg\n",
x, a, x, b);
return 1;
}
}
Actual Results: e^11356.35 - 1 = 1.00032e+4932; but expm1l(11356.35)
returned inf
Expected Results: e^11356.35 - 1 = 1.00032e+4932
Additional info:
This bug probably isn't even worth reporting, except for completeness.
expm1l is designed to compute e^x-1 more accurately when x is negative, so
[at least the i386 version] uses a slightly different algorithm than expl.
This algorithm overflows for large x where expl would not. But then, expm1
really isn't intended for large x anyway.
In my own port of the math library, I circumvent the problem by calling
__ieee754_expl when x >= 64, because at that magnitude, -1 is too small to
affect the result. This is probably overkill, but it works.
--
Summary: expm1l(x) overflows when 11356.1768 < x <= 11356.5234
Product: glibc
Version: unspecified
Status: NEW
Severity: minor
Priority: P2
Component: math
AssignedTo: aj at suse dot de
ReportedBy: petrosyan at gmail dot com
CC: glibc-bugs at sources dot redhat dot com
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
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* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
2008-02-26 7:04 [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234 petrosyan at gmail dot com
2008-02-26 7:09 ` [Bug math/5794] " petrosyan at gmail dot com
@ 2008-02-26 7:09 ` petrosyan at gmail dot com
2008-07-30 10:08 ` vda dot linux at googlemail dot com
2008-08-05 22:11 ` drepper at redhat dot com
3 siblings, 0 replies; 7+ messages in thread
From: petrosyan at gmail dot com @ 2008-02-26 7:09 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From petrosyan at gmail dot com 2008-02-26 07:08 -------
original bug filed at https://bugzilla.redhat.com/show_bug.cgi?id=43354
--
What |Removed |Added
----------------------------------------------------------------------------
Version|unspecified |2.2.5
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
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^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
2008-02-26 7:04 [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234 petrosyan at gmail dot com
@ 2008-02-26 7:09 ` petrosyan at gmail dot com
2008-02-26 7:09 ` petrosyan at gmail dot com
` (2 subsequent siblings)
3 siblings, 0 replies; 7+ messages in thread
From: petrosyan at gmail dot com @ 2008-02-26 7:09 UTC (permalink / raw)
To: glibc-bugs
--
What |Removed |Added
----------------------------------------------------------------------------
Version|2.2.5 |unspecified
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
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* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
2008-02-26 7:04 [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234 petrosyan at gmail dot com
2008-02-26 7:09 ` [Bug math/5794] " petrosyan at gmail dot com
2008-02-26 7:09 ` petrosyan at gmail dot com
@ 2008-07-30 10:08 ` vda dot linux at googlemail dot com
2008-08-05 22:11 ` drepper at redhat dot com
3 siblings, 0 replies; 7+ messages in thread
From: vda dot linux at googlemail dot com @ 2008-07-30 10:08 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From vda dot linux at googlemail dot com 2008-07-30 10:07 -------
I submitted a fix, see RH bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=43354
--
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
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* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
2008-02-26 7:04 [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234 petrosyan at gmail dot com
` (2 preceding siblings ...)
2008-07-30 10:08 ` vda dot linux at googlemail dot com
@ 2008-08-05 22:11 ` drepper at redhat dot com
3 siblings, 0 replies; 7+ messages in thread
From: drepper at redhat dot com @ 2008-08-05 22:11 UTC (permalink / raw)
To: glibc-bugs
------- Additional Comments From drepper at redhat dot com 2008-08-05 22:09 -------
Fixed in cvs.
--
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
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* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
[not found] <bug-5794-131@http.sourceware.org/bugzilla/>
2012-02-29 17:49 ` jsm28 at gcc dot gnu.org
@ 2014-07-02 7:02 ` fweimer at redhat dot com
1 sibling, 0 replies; 7+ messages in thread
From: fweimer at redhat dot com @ 2014-07-02 7:02 UTC (permalink / raw)
To: glibc-bugs
https://sourceware.org/bugzilla/show_bug.cgi?id=5794
Florian Weimer <fweimer at redhat dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Flags| |security-
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* [Bug math/5794] expm1l(x) overflows when 11356.1768 < x <= 11356.5234
[not found] <bug-5794-131@http.sourceware.org/bugzilla/>
@ 2012-02-29 17:49 ` jsm28 at gcc dot gnu.org
2014-07-02 7:02 ` fweimer at redhat dot com
1 sibling, 0 replies; 7+ messages in thread
From: jsm28 at gcc dot gnu.org @ 2012-02-29 17:49 UTC (permalink / raw)
To: glibc-bugs
http://sourceware.org/bugzilla/show_bug.cgi?id=5794
Joseph Myers <jsm28 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution| |FIXED
--- Comment #4 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-02-29 17:49:28 UTC ---
This was fixed by:
2008-08-05 Ulrich Drepper <drepper@redhat.com>
[BZ #5794]
* sysdeps/i386/fpu/s_expm1l.S: Simply use exp implementation for large
parameters.
* sysdeps/x86_64/fpu/s_expm1l.S: Likewise.
Patch by Denys Vlasenko <dvlasenk@redhat.com>.
A testcase wasn't added to the testsuite at the time. I've now proposed adding
one: http://sourceware.org/ml/libc-alpha/2012-02/msg00773.html
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end of thread, other threads:[~2014-07-02 7:02 UTC | newest]
Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2008-02-26 7:04 [Bug math/5794] New: expm1l(x) overflows when 11356.1768 < x <= 11356.5234 petrosyan at gmail dot com
2008-02-26 7:09 ` [Bug math/5794] " petrosyan at gmail dot com
2008-02-26 7:09 ` petrosyan at gmail dot com
2008-07-30 10:08 ` vda dot linux at googlemail dot com
2008-08-05 22:11 ` drepper at redhat dot com
[not found] <bug-5794-131@http.sourceware.org/bugzilla/>
2012-02-29 17:49 ` jsm28 at gcc dot gnu.org
2014-07-02 7:02 ` fweimer at redhat dot com
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