Re: [PATCH 0/2] Floating-point OE/UE exception bug

[Alex Bennée]

"Lucas Mateus Castro(alqotel)" <lucas.araujo@eldorado.org.br> writes:

> From: "Lucas Mateus Castro (alqotel)" <lucas.araujo@eldorado.org.br>
>
> Changes in v2:
>     - Completely reworked the solution:
>         * Created re_bias in FloatFmt, it is 3/4 of the total exponent
>           range of a FP type

I thought this might have an effect on the efficiency of the FloatFmt
extraction/packing but I couldn't see any real difference in fpbench. I
doubt the compiler can dead code it away if not used by a front-end.

Anyway have a:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

for the series.

>         * Added rebias bools that dictates if the result should have
>           its exponent add/subtract the re_bias value if an
>           overflow/underflow occurs.
>         * ppc_store_fpscr sets/unsets rebias if OE/UE is set/unset
>
> The PowerISA defines that if an overflow exception happen with FPSCR.OE
> set, the exponent of the intermediate result is subtracted 1536 in
> double precision operations and is added 1536 in an underflow exception,
> currently this behavior is not QEMU's behavior, this patch series fixes
> that.
>
> Currently there's no test in this patch series as there's no way to
> disable MSR.FE0 and MSR.FE1 in linux user, so any overflow/underflow
> exception with OE/UE set causes a trapping exception.

Could you do it with a system mode test? Probably overkill for this
though. I suspect tweaking testfloat would be tricky.

>
> Lucas Mateus Castro (alqotel) (2):
>   fpu: Add rebias bool, value and operation
>   target/ppc: Bugfix FP when OE/UE are set
>
>  fpu/softfloat-parts.c.inc     | 21 +++++++++++++++++++--
>  fpu/softfloat.c               |  2 ++
>  include/fpu/softfloat-types.h |  4 ++++
>  target/ppc/cpu.c              |  2 ++
>  target/ppc/fpu_helper.c       |  2 --
>  5 files changed, 27 insertions(+), 4 deletions(-)


-- 
Alex Bennée