[Beignet] [PATCH V2] libocl: refine implementation of sign().

[Zhigang Gong]

LGTM, pushed, thanks.

On Thu, Feb 12, 2015 at 02:25:58PM +0800, Ruiling Song wrote:
> Avoid if-branching.
> 
> Signed-off-by: Ruiling Song <ruiling.song at intel.com>
> ---
>  backend/src/libocl/tmpl/ocl_common.tmpl.cl |   26 +++++++++++++++++++-------
>  1 file changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/backend/src/libocl/tmpl/ocl_common.tmpl.cl b/backend/src/libocl/tmpl/ocl_common.tmpl.cl
> index db7b0d8..0ea1400 100644
> --- a/backend/src/libocl/tmpl/ocl_common.tmpl.cl
> +++ b/backend/src/libocl/tmpl/ocl_common.tmpl.cl
> @@ -17,6 +17,7 @@
>   */
>  #include "ocl_common.h"
>  #include "ocl_float.h"
> +#include "ocl_relational.h"
>  
>  /////////////////////////////////////////////////////////////////////////////
>  // Common Functions
> @@ -55,11 +56,22 @@ OVERLOADABLE float smoothstep(float e0, float e1, float x) {
>  }
>  
>  OVERLOADABLE float sign(float x) {
> -  if(x > 0)
> -    return 1;
> -  if(x < 0)
> -    return -1;
> -  if(x == -0.f)
> -    return -0.f;
> -  return 0.f;
> +// TODO: the best form of implementation is below,
> +//      But I find it hard to implement in Beignet now,
> +//      So I would put it in the TODO list.
> +
> +//      cmp.ne.f0  null    x:f  0.0:f
> +//      and        ret:ud  x:ud 0x80000000:ud
> +//(+f0) or         ret:ud  ret:ud 0x3f800000:ud
> +//      cmp.ne.f0  null    x:f  x:f
> +//(+f0) mov        ret:f   0.0f
> +
> +  union {float f; unsigned u;} ieee;
> +  ieee.f = x;
> +  unsigned k = ieee.u;
> +  float r = (k&0x80000000) ? -1.0f : 1.0f;
> +  // differentiate +0.0f -0.0f
> +  float s = 0.0f * r;
> +  s = (x == 0.0f) ? s : r;
> +  return isnan(x) ? 0.0f : s;
>  }
> -- 
> 1.7.10.4
> 
> _______________________________________________
> Beignet mailing list
> Beignet at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/beignet