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Brian Paul authored
The glsl-to-tgsi translater will emit SQRT to implement GLSL's sqrt() and distance() functions if the PIPE_SHADER_CAP_TGSI_SQRT_SUPPORTED query says it's supported by the driver. Otherwise, sqrt(x) is implemented with x*rsq(x). The problem with this is sqrt(0) must be handled specially because rsq(0) might be Inf/NaN/undefined (and then 0*rsq(0) is Inf/Nan/undefined). In the glsl-to-tgsi code we use an extra CMP to check if x is zero and then replace the result of x*rsq(x) with zero. In the end, this makes sqrt() generate much more reasonable code for drivers that can do square roots. Note that many of piglit's generated shader tests use the GLSL distance() function.
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