[Mesa-dev] [PATCH] glsl: Fix pi/2 constant in acos built-in function

[Olivier Galibert]

On Tue, Jun 05, 2012 at 04:51:54PM -0700, Paul Berry wrote:
> The best idea I've got so far would be a shader_runner test with a fragment
> shader that computes dFdx(asin(x)), compares it to the theoretical closed
> form derivative of asin(x) (which is 1/sqrt(1-x^2)), and draws red pixels
> if the result is outside a certain error tolerance.  We'd probably want to
> use a relative error (since the derivative of asin(x) can get quite large)
> and stop a bit shy of the endpoints where it goes to infinity.

Can't you take the perfectly reasonable hypothesis that the system's
asin is precise, and upload something like a 256x256 R32FG32FB32FA32F
texture with reference values?  262144 testing points should be good
enough :-)

And that's something that generalizes easily to all the functions you
may want to test on a segment.

  OG.