Hi Ilia, On 11 November 2015 at 00:28, Ilia Mirkin <imir...@alum.mit.edu> wrote: > 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. > Just checking that this hasn't fallen through the cracks. Afaics the only 'issue' with going forward is that no one has reviewed the patch yet, is that right ?
Thanks Emil _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
