Re: [Qemu-devel] [PATCH] target/i386: Return 'indefinite integer value' for invalid SSE fp->int conversions

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 6 Aug 2019 at 00:16, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 05/08/19 23:13, Richard Henderson wrote:
> > On 8/5/19 11:03 AM, Peter Maydell wrote:
> >> The x86 architecture requires that all conversions from floating
> >> point to integer which raise the 'invalid' exception (infinities of
> >> both signs, NaN, and all values which don't fit in the destination
> >> integer) return what the x86 spec calls the "indefinite integer
> >> value", which is 0x8000_0000 for 32-bits or 0x8000_0000_0000_0000 for
> >> 64-bits.  The softfloat functions return the more usual behaviour of
> >> positive overflows returning the maximum value that fits in the
> >> destination integer format and negative overflows returning the
> >> minimum value that fits.
> >>
> >> Wrap the softfloat functions in x86-specific versions which
> >> detect the 'invalid' condition and return the indefinite integer.
> >>
> >> Note that we don't use these wrappers for the 3DNow! pf2id and pf2iw
> >> instructions, which do return the minimum value that fits in
> >> an int32 if the input float is a large negative number.
> >>
> >> Fixes: https://bugs.launchpad.net/qemu/+bug/1815423
> >> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> >> ---
> >> I've tested that this fixes the LP:1815423 test case. If anybody
> >> has an x86 VM image to hand that has node.js installed it would
> >> also be useful to test the operations in
> >> https://bugs.launchpad.net/qemu/+bug/1832281
> >> (I don't have such a VM.)
> >>
> >> The other approach here would be to make the softfloat functions be
> >> flexible enough to allow this behaviour -- from my reading of IEEE754
> >> I think the exact returned result for 'invalid' inputs for float to
> >> int conversions is not specified.
> >>
> >>  target/i386/ops_sse.h | 88 +++++++++++++++++++++++++++++--------------
> >>  1 file changed, 60 insertions(+), 28 deletions(-)
> >
> > I guess this is exactly what we already do in fpu_helper.c.
> > Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> >
> >
> > r~
> >
>
> Queued, thanks.

Would you like me to do a quick respin to fix the overlong lines
that checkpatch noticed ?

thanks
-- PMM