On Apr 10, 2013, at 6:48 AM, Tobias Grosser <tob...@grosser.es> wrote:
> On 04/10/2013 02:51 PM, Michel Dänzer wrote: >> 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... > > Very interesting. This seems to be worth a comment in the source code. I agree. It would be good to document the trick being applied here so that future target writers don't have to rediscover it each time. --Owen _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
