[Mesa-dev] [PATCH] glsl: use bitwise operators in varying_matches::compute_packing_class()

[Brian Paul]

Ping, anyone?

-Brian

On 12/18/2017 09:30 PM, Brian Paul wrote:
> The mix of bitwise operators with * and + to compute the packing_class
> values was a little weird.  Just use bitwise ops instead.
>
> v2: add assertion to make sure interpolation bits fit without collision,
> per Timothy.  Basically, rewrite function to be simpler.
> ---
>   src/compiler/glsl/link_varyings.cpp | 15 ++++++++++-----
>   1 file changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/src/compiler/glsl/link_varyings.cpp b/src/compiler/glsl/link_varyings.cpp
> index 7821b1e..5d39889 100644
> --- a/src/compiler/glsl/link_varyings.cpp
> +++ b/src/compiler/glsl/link_varyings.cpp
> @@ -1982,12 +1982,17 @@ varying_matches::compute_packing_class(const ir_variable *var)
>       *
>       * Therefore, the packing class depends only on the interpolation type.
>       */
> -   unsigned packing_class = var->data.centroid | (var->data.sample << 1) |
> -                            (var->data.patch << 2) |
> -                            (var->data.must_be_shader_input << 3);
> -   packing_class *= 8;
> -   packing_class += var->is_interpolation_flat()
> +   const unsigned interp = var->is_interpolation_flat()
>         ? unsigned(INTERP_MODE_FLAT) : var->data.interpolation;
> +
> +   assert(interp < (1 << 3));
> +
> +   const unsigned packing_class = (interp << 0) |
> +                                  (var->data.centroid << 3) |
> +                                  (var->data.sample << 4) |
> +                                  (var->data.patch << 5) |
> +                                  (var->data.must_be_shader_input << 6);
> +
>      return packing_class;
>   }
>
>