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

[Andres Gomez]

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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