Re: [PATCH 1/2] softfloat: m68k: infinity is a valid encoding

["Alex Bennée" <alex.bennee@linaro.org>]

Laurent Vivier <laurent@vivier.eu> writes:

> Le 29/04/2020 à 11:26, Alex Bennée a écrit :
>> 
>> Laurent Vivier <laurent@vivier.eu> writes:
>> 
>>> Le 28/04/2020 à 20:43, Alex Bennée a écrit :
>>>>
>>>> KONRAD Frederic <frederic.konrad@adacore.com> writes:
>>>>
>>>>> The MC68881 say about infinities (3.2.4):
>>>>>
>>>>> "*For the extended precision format, the most significant bit of the
>>>>> mantissa (the integer bit) is a don't care."
>>>>>
>>>>> https://www.nxp.com/docs/en/reference-manual/MC68881UM.pdf
>>>>>
>>>>> The m68k extended format is implemented with the floatx80 and
>>>>> floatx80_invalid_encoding currently treats 0x7fff00000000000000000000 as
>>>>> an invalid encoding.  This patch fixes floatx80_invalid_encoding so it
>>>>> accepts that the most significant bit of the mantissa can be 0.
>>>>>
>>>>> This bug can be revealed with the following code which pushes extended
>>>>> infinity on the stack as a double and then reloads it as a double.  It
>>>>> should normally be converted and read back as infinity and is currently
>>>>> read back as nan:
>>>>
>>>> Do you have any real HW on which you could record some .ref files for
>>>> the various multiarch float tests we have (float_convs/float_madds)?
>>>> Does this different of invalid encoding show up when you add them?
>>>
>>> On my side, in the past when I started to implement m68k FPU, I used
>>> TestFloat and SoftFloat I have ported to m68k and I compare the result
>>> in QEMU and in a Quadra 800.
>> 
>> Surely TestFloat and SoftFloat is all emulation though?
>> 
>> Anyway if you have a Quadra 800 running Linux could you generate some
>> .ref files for the float_convs and float_madds test cases. The binaries
>> are static so you should just be able to copy them and run.
>>
> Is there any HOWTO somewhere? Or should I dig into the code as usual?

On your known good HW:

  ./float_convs > float_convs.ref

and copy the file into tests/tcg/m68k and the:

  run-float_%: float_%
          $(call run-test,$<, $(QEMU) $(QEMU_OPTS) $<,"$< on $(TARGET_NAME)")
          $(call conditional-diff-out,$<,$(SRC_PATH)/tests/tcg/$(TARGET_NAME)/$<.ref)

should automatically include the diff on the next run.

>
> Thanks,
> Laurent


-- 
Alex Bennée