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
