[Bug 89634] dEQP-GLES3: sin, cos, tan do not have enough precision

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89634

--- Comment #1 from Kenneth Graunke <kenneth at whitecape.org> ---
>From the IVB PRM, Volume 4, Part 3:

"Absolute error <= 0.0008 for the range of +/- 100* pi

 Outside of the above range the function will remain periodic, producing values
 between -1 and 1. However, the period of COS is determined by the internal
 representation of Pi, meaning that as the magnitude of input increases the
 absolute error will, in general, also increase."

Given that sin and cos are extremely common in shaders, I'm rather loathe to
emit extra shader instructions to try and make them more precise.  I imagine
most angles used by real programs will be between [-100pi, 100pi].

You can definitely construct cases that break (even producing surprising
results like sin(x) > 1.0), but as you say, the specification specifically
states that there is no precision guarantee.

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