[Bug 89648] New: dEQP-GLES3: reflect does not produce correct results for limit values

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89648

            Bug ID: 89648
           Summary: dEQP-GLES3: reflect does not produce correct results
                    for limit values
           Product: Mesa
           Version: git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Drivers/DRI/i965
          Assignee: idr at freedesktop.org
          Reporter: itoral at igalia.com
        QA Contact: intel-3d-bugs at lists.freedesktop.org

List of affected tests:

dEQP-GLES3.functional.shaders.builtin_functions.precision.reflect.highp_vertex.scalar
dEQP-GLES3.functional.shaders.builtin_functions.precision.reflect.highp_fragment.scalar

The same underlying problems described for modf (bug 89645) and mix (bug
89647): the hardware produces NaNs for some of the operations involved.

reflect(x,y) is computed as: x - 2.0 * dot(y, x) * y = x - 2.0 * x * y * y (for
scalars, but the argument is the same for vectors). If, for example, y is a
very large number so that y * y = inf, and x = 0, then we have to multiply  0
by inf and that results in NaN. The same happens if x is not 0.0, but something
very close (starting from -1.00e-38 for negative values for example) 

As with the other related bug reports, we could probably fix this by emitting
code that checks for these values specifically and resolves them directly
rather than using the formula, but that would hurt performance.

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