On Thu, Jul 7, 2016 at 10:16 AM, Ian Romanick <i...@freedesktop.org> wrote: > From: Ian Romanick <ian.d.roman...@intel.com> > > v2: Retype LZD source as UD to avoid potential problems with 0x80000000. > Suggested by Matt. Also update comment about problem values with > LZD(abs(x)). Suggested by Curro. > > Signed-off-by: Ian Romanick <ian.d.roman...@intel.com> > --- > src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 54 ++++++++++++++++++++++------ > src/mesa/drivers/dri/i965/brw_vec4_nir.cpp | 57 > ++++++++++++++++++++++++------ > 2 files changed, 90 insertions(+), 21 deletions(-) > > diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > index 65f6406..93d5e9d 100644 > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > @@ -623,8 +623,36 @@ emit_find_msb_using_lzd(const fs_builder &bld, > bool is_signed) > { > fs_inst *inst; > + fs_reg temp = src; > > - bld.LZD(retype(result, BRW_REGISTER_TYPE_UD), src); > + if (is_signed) { > + /* LZD of an absolute value source almost always does the right > + * thing. There are two problem values: > + * > + * * 0x80000000. Since abs(0x80000000) == 0x80000000, LZD returns > + * 0. However, findMSB(int(0x80000000)) == 30. > + * > + * * 0xffffffff. Since abs(0xffffffff) == 1, LZD returns > + * 31. Section 8.8 (Integer Functions) of the GLSL 4.50 spec says: > + * > + * For a value of zero or negative one, -1 will be returned. > + * > + * * Negative powers of two. LZD(abs(-(1<<x))) returns x, but > + * findMSB(-(1<<x)) should return x-1. > + *
Might be nice to add these cases to the piglit tests. 15-17 are Reviewed-by: Matt Turner <matts...@gmail.com> That should be the whole series, minus the RFC at the end. _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev