On Tue, Nov 10, 2015 at 7:24 PM, Connor Abbott <cwabbo...@gmail.com> wrote: > On Tue, Nov 10, 2015 at 7:02 PM, Ilia Mirkin <imir...@alum.mit.edu> wrote: >> On Tue, Nov 10, 2015 at 6:44 PM, Eric Anholt <e...@anholt.net> wrote: >>> Ilia Mirkin <imir...@alum.mit.edu> writes: >>> >>>> In nv50, and in the python script that Rob circulated, we do: >>>> >>>> bld.mkCmp(OP_SET, CC_GE, TYPE_U32, (s = bld.getSSA()), TYPE_U32, m, b); >>>> >>>> Do the same in the nir div lowering pass. This fixes the large-udiv-udiv >>>> piglit tests on freedreno. >>> >>> I assume you meant *-op-div-large-uint-uint.shader_test. >> >> Yes. >> >>> >>> vc4 doesn't have uge yet, but I've got a patch to add it and it does >>> fix one subtest. What this lowering pass is actually doing has never >>> really made sense to me, but it works, so: >>> >>> Acked-by: Eric Anholt <e...@anholt.net> >> >> It's a magical sequence of non-sensical operations which appear to >> produce the proper result with high probability... what's so confusing >> about that? :) >> >> More seriously, I think there are Newton-Raphson overtones in what >> it's doing, but I never fully traced it down. It kind of loses me >> after subtracting 2 from the integer representation of the float bits. >> _______________________________________________ >> mesa-dev mailing list >> mesa-dev@lists.freedesktop.org >> http://lists.freedesktop.org/mailman/listinfo/mesa-dev > > Where did you get it from? Is there a paper somewhere explaining it? I > sort of have a morbid curiosity, perhaps because I got sucked into > implementing division/sqrt/rsq for doubles.
I made the old freedreno impl based on nv50's div lowering code. There's similarly weird code for r600, but I don't know if the r600 or nv50 code came first, or where they came from. FWIW the nvc0 div logic is quite different (implemented as a function call, which does rather different things... I think). I also don't know where that came from. Sorry! _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
