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

[Andres Gomez]

Hi,

I haven't had any other feedback than Ilia's (thanks Ilia!) so my
doubts still stand.

I'd welcome more info regarding this topic.

Thanks!

Br.

On Tue, 2016-03-15 at 17:46 +0200, Andres Gomez 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?
> 
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-- 
Br,

Andres