On Wed, May 4, 2016 at 10:05 AM, Andres Gomez <ago...@igalia.com> wrote: > 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?
Yes, I agree. I noticed the "trunc" test provided some tolerance, and really... it shouldn't. We should be able to calculate trunc (and a bunch of other functions like you mention) exactly. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev
