Re: [Qemu-devel] [PATCH] fpu/softfloat: check for Inf / x or 0 / x before /0

[Peter Maydell]

On 17 April 2018 at 22:27, Emilio G. Cota <address@hidden> wrote:
> BTW I just checked with -t host on an IBM Power8, and we get
> the same 1049 flag errors we get with -t soft plus two additional ones:
>
> +A 0xffb00000, expected: 0x7fa00000, returned: 0x7fa00000, \
>   expected exceptions: i, returned: none
> +error: flags mismatch for input @ ibm/Basic-Types-Inputs.fptest:382:
> +b32A =0 S -> S i

That's Abs of an SNaN; the test expects Invalid, which is wrong,
because IEEE754 says absolute-value is a "quiet-computational
operation" that never signals an exception.

What's odd is that we don't report that error for the softfloat
implementation! I also don't understand why the expected value
isn't just the input value with the sign bit flipped.

> (...)
> +cff 0xffb00000, expected: 0x7ff8000000000000, returned: 0x7ff4000000000000, \
>   expected exceptions: i, returned: none
> +error: flags mismatch for input @ ibm/Basic-Types-Inputs.fptest:26170:
> +b32b64cff =0 S -> Q i

SNaN conversion from 32 bit to 64 bit. Here I agree
with the test -- we should quieten the NaN and raise
Invalid -- which implies that the hardware is wrong ?!?

thanks
-- PMM