[Bug c/38352] New: cos() returns incorrect value in FE_UPWARD rounding mode

[kruppaal at loria dot fr]

The attached test case produces the erroneous value of -20763584.029346 for
cos(2 * Pi / 4) when the rounding mode is set to FE_UPWARD, instead of the
correct value (close to) 0. Other rounding modes do not show this error,
compiling with optimization enabled (-O1, -O2 or -O3) or as a 32 bit binary
with -m32 also do not show the error. If the binary is linked statically with
-static, the bug disappears as well.

Compile with

gcc -O0 -o cos_bug cos_bug.c -lm

Compilers used (both show the bug) are

gcc (GCC) 4.3.2

and 

gcc (GCC) 4.3.0 20080428 (Red Hat 4.3.0-8)

Processor is 

Intel(R) Core(TM)2 CPU 6400  @ 2.13GHz.

Math library is from
Redhat Fedora 9, glibc-2.8-8.x86_64 package.


-- 
           Summary: cos() returns incorrect value in FE_UPWARD rounding mode
           Product: gcc
           Version: 4.3.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kruppaal at loria dot fr
  GCC host triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38352