Problems with floating point exception flags

[Marcel Moolenaar]

On Wed, May 05, 2004 at 09:31:38PM -0700, David Schultz wrote:
> On Wed, May 05, 2004, Marcel Moolenaar wrote:
> > On Tue, May 04, 2004 at 06:39:04AM -0700, David Schultz wrote:
> > > 
> > > Here is a better kernel patch.  Instead of treating all the bits
> > > of the FPCR as sticky, it merely treats the exception flags that
> > > way.  After reading the source carefully, I'm pretty sure this is
> > > the right fix, but I can't test it without working hardware.
> > > I also uncovered a bug in the way the software floating-point
> > > routines handle underflow.  See below.
> > 
> > I built and booted a kernel with these patches. Trying to exercise the
> > code with the files at http://people.freebsd.org/~das/alpha yield:
> 
> Thanks!
> 
> > alpha% ./te
> > Should be 00: 00
> > Floating exception (core dumped)
> > May  5 19:00:11 alpha kernel: pid 638 (te), uid 4152: exited on signal 8 (core dumped)
> 
> You need to compile the program with gcc's -mieee option in order
> to get floating point to work in a reasonable way on alpha.  If
> you could try the program compiled with -mieee, that would be great.

Attached a fix for fenv.h. All files newly downloaded from ~das/alpha

alpha% cc -g -mieee -o te te.c
alpha% ./te
Should be 00: 00
Should be 14: 14
Should be 1c: 1c
Should be 1e: 1e
Should be 1e: 1e

alpha% cc -g -mieee -o test-fenv test-fenv.c -lm
main() in test-fenv.c:111, "fetestexcept(FE_ALL_EXCEPT) == 0"
main() in test-fenv.c:117, "fetestexcept(FE_ALL_EXCEPT) == 0"
main() in test-fenv.c:121, "fetestexcept(ALL_STD_EXCEPT) == (ALL_STD_EXCEPT & ~FE_DIVBYZERO)"
main() in test-fenv.c:125, "fetestexcept(FE_ALL_EXCEPT) == FE_INEXACT"
main() in test-fenv.c:127, "fetestexcept(FE_ALL_EXCEPT) == 0"
main() in test-fenv.c:131, "fetestexcept(FE_ALL_EXCEPT) == FE_INEXACT"
main() in test-fenv.c:134, "fetestexcept(FE_ALL_EXCEPT) == (FE_INEXACT | FE_DIVBYZERO | FE_UNDERFLOW)"
main() in test-fenv.c:136, "fetestexcept(FE_ALL_EXCEPT) == 0"
main() in test-fenv.c:139, "(fegetmask() & ALL_STD_EXCEPT) == 0"
main() in test-fenv.c:143, "fetestexcept(ALL_STD_EXCEPT) == FE_DIVBYZERO"
main() in test-fenv.c:146, "expecting_trap == 0"
main() in test-fenv.c:148, "fetestexcept(ALL_STD_EXCEPT) == 0"
main() in test-fenv.c:153, "fetestexcept(ALL_STD_EXCEPT) == 0"
main() in test-fenv.c:156, "expecting_trap == 0"
main() in test-fenv.c:158, "fetestexcept(ALL_STD_EXCEPT) == 0"
main() in test-fenv.c:160, "(fegetmask() & ALL_STD_EXCEPT) == 0"
main() in test-fenv.c:165, "fegetround() == FE_DOWNWARD"
main() in test-fenv.c:166, "getround() == FE_DOWNWARD"
main() in test-fenv.c:168, "getround() == FE_UPWARD"
main() in test-fenv.c:169, "fegetround() == FE_UPWARD"
main() in test-fenv.c:171, "getround() == FE_TOWARDZERO"
main() in test-fenv.c:172, "fegetround() == FE_TOWARDZERO"
main() in test-fenv.c:179, "getround() == FE_DOWNWARD"
main() in test-fenv.c:181, "getround() == FE_UPWARD"

FYI,

-- 
 Marcel Moolenaar	  USPA: A-39004		 marcel at xcllnt.net