[Mesa-dev] [PATCH 4/6] Bitwise conversion operator support in ir_constant_expression.

[Jose Fonseca]

----- Original Message -----
> This patch expects to be applied after the "Constants through
> builtins
> evaluation rewrite" for two reasons:
> - a line of that patch appears in the context
> - the ir_function side changes that the old method would need are not
>   present (and they would conflict)
> 
> At that point a "test_out = floatBitsToUint(-1.0);" fired through the
> glsl compiler gives a correct "(assign (x) (var_ref test_out)
> (constant uint (3212836864)))"
> 
> Signed-off-by: Olivier Galibert <galibert at pobox.com>
> ---
>  src/glsl/ir_constant_expression.cpp |   47
>  +++++++++++++++++++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/src/glsl/ir_constant_expression.cpp
> b/src/glsl/ir_constant_expression.cpp
> index 61c0ae6..5923bb4 100644
> --- a/src/glsl/ir_constant_expression.cpp
> +++ b/src/glsl/ir_constant_expression.cpp
> @@ -71,6 +71,29 @@ dot(ir_constant *op0, ir_constant *op1)
>     return result;
>  }
>  
> +/* This method is the only one supported by gcc.  Unions in
> particular
> + * are iffy, and read-through-converted-pointer is killed by strict
> + * aliasing.  OTOH, the compiler sees through the memcpy, so the
> + * resulting asm is reasonable.
> + */
> +static float
> +bitcast_u2f(unsigned int u)
> +{
> +   assert(sizeof(float) == sizeof(unsigned int));
> +   float f;
> +   memcpy(&f, &u, sizeof(f));
> +   return f;
> +}
> +
> +static unsigned int
> +bitcast_f2u(float f)
> +{
> +   assert(sizeof(float) == sizeof(unsigned int));
> +   unsigned int u;
> +   memcpy(&u, &f, sizeof(f));
> +   return u;
> +}
> +
>  ir_constant *
>  ir_rvalue::constant_expression_value(struct hash_table
>  *variable_context)
>  {
> @@ -207,6 +230,30 @@ ir_expression::constant_expression_value(struct
> hash_table *variable_context)
>  	 data.u[c] = op[0]->value.i[c];
>        }
>        break;
> +   case ir_unop_bitcast_i2f:
> +      assert(op[0]->type->base_type == GLSL_TYPE_INT);
> +      for (unsigned c = 0; c < op[0]->type->components(); c++) {
> +	 data.f[c] = bitcast_u2f(op[0]->value.i[c]);

Shouldn't it be bitcast_i2f ?

> +      }
> +      break;
> +   case ir_unop_bitcast_f2i:
> +      assert(op[0]->type->base_type == GLSL_TYPE_FLOAT);
> +      for (unsigned c = 0; c < op[0]->type->components(); c++) {
> +	 data.i[c] = bitcast_f2u(op[0]->value.f[c]);

And bitcast_f2i here ?

> +      }
> +      break;
> +   case ir_unop_bitcast_u2f:
> +      assert(op[0]->type->base_type == GLSL_TYPE_UINT);
> +      for (unsigned c = 0; c < op[0]->type->components(); c++) {
> +	 data.f[c] = bitcast_u2f(op[0]->value.u[c]);
> +      }
> +      break;
> +   case ir_unop_bitcast_f2u:
> +      assert(op[0]->type->base_type == GLSL_TYPE_FLOAT);
> +      for (unsigned c = 0; c < op[0]->type->components(); c++) {
> +	 data.u[c] = bitcast_f2u(op[0]->value.f[c]);
> +      }
> +      break;
>     case ir_unop_any:
>        assert(op[0]->type->is_boolean());
>        data.b[0] = false;
> --
> 1.7.10.rc3.1.gb306
> 
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