[Bug 89640] New: dEQP-GLES3: tanh produces incorrect results for some limit cases

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89640

            Bug ID: 89640
           Summary: dEQP-GLES3: tanh produces incorrect results for some
                    limit cases
           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.tanh.highp_vertex.scalar
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_vertex.vec2
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_vertex.vec3
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_vertex.vec4
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_fragment.scalar
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_fragment.vec2
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_fragment.vec3
dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh.highp_fragment.vec4

tanh is implemented as:

   body.emit(ret(div(sub(exp(x), exp(neg(x))),
                     add(exp(x), exp(neg(x))))));

For some values of x this leads to a infinity values in the denominator and
numerator. The division of such values leads to a NaN instead of 1.0 (the
result expected by dEQP and the result of tanh from libc too).

I suppose we can add as-hoc code to handle these cases and produce a result of
1.0 directly in software when we detect them, but I wonder if it is worth the
cost.

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