[Bug math/369] New: pow problems on x86

[Bug math/369] New: pow problems on x86

[vargaz at gmail dot com]

Consider the following test program:
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
#include <stdio.h>
#include <math.h>

void main() {
        double d;

        d = pow (-2, 1E300);
        printf ("D: %f.\n", d);

        d = pow (-2, -1E300);
        printf ("D: %f.\n", d);
}
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Under x86 linux, this prints out:

D: nan.
D: nan

I think the answer should be +inf and 0, respectively. Both
solaris,
windows, and the IBM Accurate Portable Mathematical library
returns
these values, so I think this might be a bug in the assembly
language
pow routine in glibc.

-- 
           Summary: pow problems on x86
           Product: glibc
           Version: 2.3.2
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: aj at suse dot de
        ReportedBy: vargaz at gmail dot com
                CC: glibc-bugs at sources dot redhat dot com
  GCC host triplet: i686-pc-linux-gnu


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[Bug math/369] pow problems on x86

[aj at suse dot de]

------- Additional Comments From aj at suse dot de  2004-12-18 15:37 -------
The report is confirmed.  On other platforms we get the expected result.

Uli, could you look into this, please?

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           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|aj at suse dot de           |drepper at redhat dot com
             Status|NEW                         |ASSIGNED


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[Bug math/369] pow problems on x86

[steven at gcc dot gnu dot org]

------- Additional Comments From steven at gcc dot gnu dot org  2006-05-07 14:57 -------
It seems I've run into this one now, too.  What happened to this bug?


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           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |steven at gcc dot gnu dot
                   |                            |org


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[Bug math/369] pow problems on x86

[nikolay dot zhuravlev at auriga dot ru]

------- Additional Comments From nikolay dot zhuravlev at auriga dot ru  2006-06-15 09:17 -------
I built glibc from CVS on 2006/06/14 and the bug is still there.
I think the culprit is the assembler code in __ieee754_pow.

POSIX wants HUGE_VAL for pow(-2, 1E300).

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|2.3.2                       |2.4


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[Bug math/369] pow problems on x86

[nikolay dot zhuravlev at auriga dot ru]

------- Additional Comments From nikolay dot zhuravlev at auriga dot ru  2006-06-15 09:23 -------
Changed version to 'unspecified' since it is in the trunk

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
            Version|2.4                         |unspecified


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[Bug math/369] pow problems on x86

[eberlein at us dot ibm dot com]

------- Additional Comments From eberlein at us dot ibm dot com  2006-08-31 22:27 -------
Created an attachment (id=1269)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=1269&action=view)
patch for pow to return inf/0 for (-2,+/-1E300)

I've created a patch to return inf for pow(-2,1E300) and 0 for pow(-2,-1E300). 
This patch modifies the function to use |x| and filter the result if x < 0,
keeping inf or zero, otherwise return NaN.


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[Bug math/369] pow problems on x86

[eberlein at us dot ibm dot com]

------- Additional Comments From eberlein at us dot ibm dot com  2006-08-31 22:32 -------
Created an attachment (id=1270)
 --> (http://sourceware.org/bugzilla/attachment.cgi?id=1270&action=view)
patch for pow to return inf/0 for (-2,+/-1E300)

oops, fixing the diff since it had some control chars accidentally pasted into
the file.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
Attachment #1269 is|0                           |1
           obsolete|                            |


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[Bug math/369] pow problems on x86

[ismail at pardus dot org dot tr]

------- Additional Comments From ismail at pardus dot org dot tr  2007-12-15 09:46 -------
Still affects glibc 2.7

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                 CC|                            |ismail at pardus dot org dot
                   |                            |tr


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[Bug math/369] pow problems on x86

[mtk dot manpages at gmail dot com]

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           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mtk dot manpages at gmail
                   |                            |dot com


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[Bug math/369] pow problems on x86

[mtk dot manpages at gmail dot com]

------- Additional Comments From mtk dot manpages at gmail dot com  2008-07-30 09:17 -------
Still present in glibc 2.8

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[Bug math/369] pow problems on x86

[mtk dot manpages at gmail dot com]

------- Additional Comments From mtk dot manpages at gmail dot com  2010-09-12 05:44 -------
Still present in glibc 2.12.1, where we get:

D: -nan.
D: -nan.

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[Bug math/369] pow problems on x86

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=369

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

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

--- Comment #13 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-03-28 15:01:45 UTC ---
Fixed by:

commit d6270972f79fe89a96fa7a3909991dad2e317033
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Wed Mar 28 14:57:58 2012 +0000

    Fix pow of negative numbers to integer exponents (bugs 369, 2678, 3866).

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[Bug math/369] pow problems on x86

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=369

--- Comment #12 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-03-27 16:02:37 UTC ---
The attached patch is incorrect (it results in NaN for pow (-1, DBL_MAX), which
should be 1; an infinity for pow (-DBL_MAX, 1000.5), which should be NaN; zero
for pow (-DBL_MIN, 1000.5), which should be NaN).  I'm working on a different
patch.

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[Bug math/369] pow problems on x86

[bonzini at gnu dot org]

http://sourceware.org/bugzilla/show_bug.cgi?id=369

Paolo Bonzini <bonzini at gnu dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bonzini at gnu dot org

--- Comment #11 from Paolo Bonzini <bonzini at gnu dot org> 2012-03-22 23:21:04 UTC ---
The patch looks good to me from the x86 point of view, but I cannot really say
anything about the math.

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[Bug math/369] pow problems on x86

[jsm28 at gcc dot gnu.org]

http://sourceware.org/bugzilla/show_bug.cgi?id=369

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |NEW
         AssignedTo|drepper.fsp at gmail dot    |unassigned at sourceware
                   |com                         |dot org

--- Comment #10 from Joseph Myers <jsm28 at gcc dot gnu.org> 2012-02-22 21:27:13 UTC ---
Still present.  Could one of our x86 experts review Pete Eberlein's patch from
2006?

Testcases are certainly needed for libm-test.inc for a fix to go in - both
tests for the particular cases here, and tests for more normal cases of powers
of negative numbers (negative number to small (+ve and -ve) even powers,
negative number to small (+ve and -ve) odd powers).  Cases involving infinities
and zeros as arguments seem better covered in the testsuite and there are
already tests of negative numbers to fractional powers.

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