On Thu, Feb 25, 2016 at 2:15 AM, Iago Toral Quiroga <ito...@igalia.com> wrote: > From the OpenGL 4.2 spec: > > "When a constructor is used to convert any integer or floating-point type to a > bool, 0 and 0.0 are converted to false, and non-zero values are converted to > true." > > Thus, even the smallest non-zero floating value should be translated to true. > This behavior has been verified also with proprietary NVIDIA drivers.
Ooh, interesting. > Currently, we implement this conversion as a cmp.nz operation with floats, > subject to floating-point precision limitations, and as a result, relatively > small non-zero floating point numbers return false instead of true. > > This patch fixes the problem by getting rid of the sign bit (to cover the case > of -0.0) and testing the result against 0u using an integer comparison > instead. > --- > src/mesa/drivers/dri/i965/brw_fs_nir.cpp | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > index db20c71..7d62d7e 100644 > --- a/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > +++ b/src/mesa/drivers/dri/i965/brw_fs_nir.cpp > @@ -913,9 +913,18 @@ fs_visitor::nir_emit_alu(const fs_builder &bld, > nir_alu_instr *instr) > bld.MOV(result, negate(op[0])); > break; > > - case nir_op_f2b: > - bld.CMP(result, op[0], brw_imm_f(0.0f), BRW_CONDITIONAL_NZ); > - break; > + case nir_op_f2b: { > + /* Because comparing to 0.0f is subject to precision limitations, do > the > + * comparison using integers (we need to get rid of the sign bit for > that) > + */ > + if (devinfo->gen >= 8) > + op[0] = resolve_source_modifiers(op[0]); Oh, good thinking. > + op[0] = retype(op[0], BRW_REGISTER_TYPE_UD); > + bld.AND(op[0], op[0], brw_imm_ud(0x7FFFFFFFu)); > + bld.CMP(result, op[0], brw_imm_ud(0u), BRW_CONDITIONAL_NZ); The cmod_propagation is going to turn this into an AND.NZ, which we may as well just do here: set_condmod(BRW_CONDITIONAL_NZ, bld.AND(result, op[0], brw_imm_ud(0x7FFFFFFFu)); > + break; Bad indentation. With those two things changed in both patches, they are Reviewed-by: Matt Turner <matts...@gmail.com> _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/mesa-dev