On Mit, 2013-04-10 at 12:59 +0200, Christian König wrote: > Am 10.04.2013 12:21, schrieb Michel Dänzer: > > On Mit, 2013-04-10 at 12:07 +0200, Christian König wrote: > >> Am 10.04.2013 11:46, schrieb Michel Dänzer: > >> > >> But why the heck is multiplying with 0x4f800000 fixing the result? > > I'm afraid I can't explain how it works, I basically copied it from the > > Cayman section in R600Instructions.td...
[...] > Anyway even if I can't explain exactly why it seems to work fine on both > Cayman and SI, so the patch is: > > Reviewed-by: Christian König <christian.koe...@amd.com> Thanks. I think I can actually explain again how it works: The unsigned integer input value is converted to float, its reciprocal value is computed and multiplied by (1 << 32) (encoded as 0x4f800000 in floating point) and converted back to unsigned integer. I think this might lose up to 8 of the least significant bits of the result... -- Earthling Michel Dänzer | http://www.amd.com Libre software enthusiast | Debian, X and DRI developer _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
