On Thu, Nov 19, 2015 at 11:35 AM, Kristian Høgsberg <k...@bitplanet.net> wrote: > On Thu, Nov 19, 2015 at 11:24 AM, Matt Turner <matts...@gmail.com> wrote: >> On Thu, Nov 19, 2015 at 9:30 AM, Kristian Høgsberg <k...@bitplanet.net> >> wrote: >>> On Thu, Nov 19, 2015 at 2:05 AM, Iago Toral Quiroga <ito...@igalia.com> >>> wrote: >>>> From: Connor Abbott <connor.w.abb...@intel.com> >>>> >>>> If we tried to get/set something that was exactly 64 bits, we would >>>> try to do (1 << 64) - 1 to calculate the mask which doesn't give us all >>>> 1's like we want. >>>> >>>> v2 (Iago) >>>> - Replace ~0 by ~0ull >>>> - Removed unnecessary parenthesis >>>> >>>> Reviewed-by: Iago Toral Quiroga <ito...@igalia.com> >>>> --- >>>> src/mesa/drivers/dri/i965/brw_inst.h | 6 ++++-- >>>> 1 file changed, 4 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/src/mesa/drivers/dri/i965/brw_inst.h >>>> b/src/mesa/drivers/dri/i965/brw_inst.h >>>> index 4ed95c4..ec08194 100644 >>>> --- a/src/mesa/drivers/dri/i965/brw_inst.h >>>> +++ b/src/mesa/drivers/dri/i965/brw_inst.h >>>> @@ -694,7 +694,8 @@ brw_inst_bits(const brw_inst *inst, unsigned high, >>>> unsigned low) >>>> high %= 64; >>>> low %= 64; >>>> >>>> - const uint64_t mask = (1ull << (high - low + 1)) - 1; >>>> + const uint64_t mask = (high - low == 63) ? ~0ull : >>>> + (1ull << (high - low + 1)) - 1; >>> >>> Can we do >>> >>> const uint64_t mask = (~0ul >> (64 - (high - low + 1))); >>> >>> instead? >> >> I don't think so, because ~0ul is of type unsigned, so right shifting >> it shifts in zeros. I was going to make a similar comment on the >> original patch -- "-1" is preferable over ~0u with an increasingly >> long sequence of l's because it's signed, so it's sign extended to >> fill whatever you assign it to. In your code though, since it's an >> operand we'd need -1ll, I think... > > No, shifting in zeros is the whole point. We start out with 64 1 bits, > then shift it down enough that we end up with (high - low + 1) 1 bits > at the bottom, which is what we're trying to compute.
Doh. Of course. :) _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
