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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo