[Bug math/14273] New: cosh() returns incorrect results

["pdemarco at maplesoft dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14273

             Bug #: 14273
           Summary: cosh() returns incorrect results
           Product: glibc
           Version: 2.15
            Status: NEW
          Severity: critical
          Priority: P2
         Component: math
        AssignedTo: unassigned@sourceware.org
        ReportedBy: pdemarco@maplesoft.com
    Classification: Unclassified


cosh() returns incorrect results in the most recent version of libm.  
Here is an example:

ubuntu64ma337>> cat test.c
#include <stdio.h>
#include <math.h>

int main(int argv, char *argc[])
        {
        double np = 709.889355812725967;
        printf("%g\n", cosh(709.889355812725967) );
        printf("%g\n", cosh(np) );
        double nm = -709.889355812725967;
        printf("%g\n", cosh(-709.889355812725967) );
        printf("%g\n", cosh(nm) );
        return 0;
        }
ubuntu64ma337>> gcc test.c -lm
ubuntu64ma337>> a.out
1e+308
1e+308
1e+308
inf


The last result is wrong.

I believe this is because of the following change made to glibc 2.15:

* Integrate libm with gcc's -ffinite-math-only option.
   Implemented by Ulrich Drepper.

Note that http://gcc.gnu.org/onlinedocs/gcc-3.3.6/g77/Optimize-Options.html has
this to say about the finite-math-only option:

-ffinite-math-only
Allow optimizations for floating-point arithmetic that assume that arguments
and results are not NaNs or +-Infs. 
This option should never be turned on by any -O option since it can result in
incorrect output for programs which depend on an exact implementation of IEEE
or ISO rules/specifications. 
The default is -fno-finite-math-only.

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