Hi all this might be of general interest to render, composite, and paint and other tools in blender so thought I'd forward it,
LetterRip ---------- Forwarded message ---------- From: Cyrille Berger <cber...@cberger.net> Date: Tue, Apr 20, 2010 at 1:31 PM Subject: Lookup table and float to int conversion and performance To: Krita's developers and users mailing list <kimages...@kde.org> Hello, Since pippin has been poking us on irc on using lookup table with floats, I wrote a class that do exactly that, code is in [1]. I did a few tests, and I get a 4 times improvement on computation of sinus, and 2.5 times improvement on computation of sqrt. An other fact with floating point that have come to my attention recently is that conversion to integer is painfully slow, for more details see [2]. And using a lookup table is a possible solution see [3] and [4] for what gegl people did. Using the floating point lookup table, I noticed 19 times improvement on float->uint8, and 1.22 times improvement on float->uint32. But more interestingly for our case is the suggestion by [2] to use the 'lrintf' function, which is part of the C99 standard, this function gives 44 times improvement on float->uint8 and 2.5 times on float->uint32, of course it is not totally a replacement for cast since it is a round function, but I think in most of our uses, it is good enough. Also 'lrintf' is not available under MSVC, so we will probably have to wrap it to be portable to Windows (most likely in KoColorSpaceMaths). It is worth to note that there is an even faster way, but it involves assembly, and I am not sure the gain is worth the pain, not counting that it is assuming that the FPU is in a good state, which is generally the case, but not guaranteed. The conclusion I take from this is that we need to be careful in conversion from float to integer, check when it happen, and only do it when it is absolutely needed. And for 2.3, I intend to make the color spaces use 'lrintf', and start using the lut [1]. [1] http://bitbucket.org/cyrille/lut [2] http://www.mega-nerd.com/FPcast/ [3] http://www.gimpusers.com/forums/gegl-developer/227-speeding-up-GEGL- operations-in-GIMP.html [4] http://mysite.verizon.net/spitzak/conversion/sketches_0265.pdf -- Cyrille Berger _______________________________________________ kimageshop mailing list kimages...@kde.org https://mail.kde.org/mailman/listinfo/kimageshop _______________________________________________ Bf-committers mailing list Bf-committers@blender.org http://lists.blender.org/mailman/listinfo/bf-committers
