[Mesa-dev] About border values in fp64 conversion tests

[Ilia Mirkin]

Not really an answer to your question, but you may be interested in
this model of the NVIDIA Tesla FPU that mwk RE'd, including fp64
(which was available on the G200 only in that series). I have no
reason to believe that Fermi+ are substantially different:

https://github.com/envytools/envytools/blob/master/nvhw/fp.c

You can see how the instructions map to these here:
https://github.com/envytools/envytools/blob/master/hwtest/g80_fp64.c

Hope this helps (or is at least a little bit interesting).

  -ilia


On Tue, Mar 15, 2016 at 11:46 AM, Andres Gomez <agomez at igalia.com> wrote:
> Hi,
>
> as complementary work to the one done to "Add FP64 support to the i965
> shader backends" at:
> https://bugs.freedesktop.org/show_bug.cgi?id=92760
>
> I've been working to add piglit tests that would check the new features
> added by this addition.
>
> One of the topics we have been creating tests for is implicit/explicit
> conversion from and to doubles in GLSL. We have created already a
> generator for it but have some doubts about what to expect when dealing
> with conversions from a value out of range in the destination type.
>
> Specifically, I'm talking about negative doubles explicitly converted
> into unsigned int or too big negative or positive double values
> converted into int or unsigned int.
>
> What I've observed from running with the NVIDIA proprietary driver or
> with other backends is that, typically, the conversion will result in a
> value which is the lowest or the highest defined in the destination
> type, depending on the side of the happening overflow.
>
> However, I've been unable to find documentation in the GLSL specs
> specifying how the conversions should work in this cases.
>
> My conclusion is that the behavior is undefined and will depend on
> implementation. Hence, we won't add tests for these cases.
>
> Opinions?
>
> --
> Br,
>
> Andres
>
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