[Bug math/15388] New: Erroneous output from floating point tan

[Bug math/15388] New: Erroneous output from floating point tan

[simplyrahul17 at gmail dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15388

             Bug #: 15388
           Summary: Erroneous output from floating point tan
           Product: glibc
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: simplyrahul17@gmail.com
    Classification: Unclassified


On executing the following code (compiled with g++ 4.6.3 on Intel(R) Core(TM)
i7-2600 CPU @ 3.40GHz running Ubuntu 12.04.1 LTS):

#include<cmath>
#include<stdio.h>
using namespace std;
int main()
{
 float f = 4386557896710122704971697171202048.0;
 printf("%.16f\n", tan(f));
 return 0;
}

I get the output as 33554432.0
The expected output is 97800744.0

In hex, this means libm says
tan(0x77584625) = 0x4C000000
However, the output should be 0x4CBA8A45.

The "correct" output was obtained using WolframAlpha
(97800745.2669871207241704332677514328806018068212018723832)
and one other compiler does produce the right output
(in hex 0x4CBA8A45, in decimal 97800744.0)
for the same program.

I know that the input is a bit strange, but looking at the hex
it seems to be a valid representable floating point number.
Using double instead of float makes the problem go away.

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[Bug math/15388] Erroneous output from floating point tan

[aj at suse dot de]

http://sourceware.org/bugzilla/show_bug.cgi?id=15388

Andreas Jaeger <aj at suse dot de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING
                 CC|                            |aj at suse dot de

--- Comment #1 from Andreas Jaeger <aj at suse dot de> 2013-04-23 07:00:56 UTC ---
Compiling and running the program, I get:
./a.out 
97800744.0000000000000000

Which glibc version and which architecture is your program running on?

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[Bug math/15388] Erroneous output from floating point tan

[siddhesh at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15388

Siddhesh Poyarekar <siddhesh at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
                 CC|                            |siddhesh at redhat dot com
         Resolution|                            |DUPLICATE

--- Comment #2 from Siddhesh Poyarekar <siddhesh at redhat dot com> 2013-04-23 09:38:19 UTC ---
This was fixed in 2.17 with the following commit:

commit 7a845b2c237434d4aad790aaba3a973e24ea802f
Author: Joseph Myers <joseph@codesourcery.com>
Date:   Tue Jul 3 17:10:42 2012 +0000

    Fix float range reduction problems (bug 14283).

*** This bug has been marked as a duplicate of bug 14283 ***

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[Bug math/15388] Erroneous output from floating point tan

[fweimer at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15388

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
              Flags|                            |security-

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