Hi, as part of the work done to "Add FP64 support to the i965 shader backends" at: https://bugs.freedesktop.org/show_bug.cgi?id=92760
I've been working to add piglit tests that would check the new features added by this addition. Due to this, I've been checking and making modifications into the builtin_functions*py module used by some generators. These modules use automatic calculation of the tolerance when distance checking the result of a function. As already stated in the good documentation of the module, the tolerance is computed following what it is stated in OpenGL's specs: From the OpenGL 1.4 spec (2.1.1 "Floating-Point Computation"): "We require simply that numbers' floating-point parts contain enough bits ... so that individual results of floating-point operations are accurate to about 1 part in 10^5." Although the text is open to interpretation, and for specific operations we take a little bit more flexible approach, basically, the tolerance is calculated as: tolerance = <expected_value> / 10⁵ This makes sense since the precision of a floating point value gets reduced while the number gets bigger[1]. Following this approach, for a number in the order of 40*10⁵, the tolerance used is ~40. While this should be OK for most of the functions, it seems to me that such a high tolerance should not be used with specific functions, if any tolerance should be used at all. For example, when testing the "sign()" function, seems pretty obvious that using a value of 40 in the tolerance of a function that should return either 1.0, 0.0 or -1.0 doesn't make much sense. A similar case is the "trunc" function and probably others, like "floor", "ceil", "abs", etc. My conclusion is that it should be safe to assume no tolerance in this functions and I could modify the algorithm used for them in the python module but I wanted to have some feedback in case I'm not taking into account something that advices against doing these modifications. Opinions? [1] https://en.wikipedia.org/wiki/IEEE_floating_point#Basic_and_interch ange_formats -- Br, Andres
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