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

[Zhigang Gong]

On Thu, Jan 29, 2015 at 03:40:27PM +0800, Ruiling Song wrote:
> Avoid if-branching.
> 
> Signed-off-by: Ruiling Song <ruiling.song at intel.com>
> ---
>  backend/src/libocl/src/ocl_geometric.cl |   19 ++++++-------------
>  1 file changed, 6 insertions(+), 13 deletions(-)
> 
> diff --git a/backend/src/libocl/src/ocl_geometric.cl b/backend/src/libocl/src/ocl_geometric.cl
> index 07f1419..baa2f85 100644
> --- a/backend/src/libocl/src/ocl_geometric.cl
> +++ b/backend/src/libocl/src/ocl_geometric.cl
> @@ -60,30 +60,23 @@ OVERLOADABLE float distance(float2 x, float2 y) { return length(x-y); }
>  OVERLOADABLE float distance(float3 x, float3 y) { return length(x-y); }
>  OVERLOADABLE float distance(float4 x, float4 y) { return length(x-y); }
>  OVERLOADABLE float normalize(float x) {
> -  union { float f; unsigned u; } u;
> -  u.f = x;
> -  if(u.u == 0)
> -    return 0.f;
> -  if(isnan(x))
> -    return NAN;
> -  return u.u < 0x7fffffff ? 1.f : -1.f;
> +  float m = length(x);
> +  m = m == 0.0f ? 1.0f : m;
> +  return x / m;
>  }
>  OVERLOADABLE float2 normalize(float2 x) {
>    float m = length(x);
> -  if(m == 0)
> -    return 0;
> +  m = m == 0.0f ? 1.0f : m;
>    return x / m;
>  }

Although eliminate branching, but introduce one more div if the
length is zero. If a test case has many zero vectors, then this
patch may bring some performance regression, as division is
relatively expensive.

Any thoughts?


>  OVERLOADABLE float3 normalize(float3 x) {
>    float m = length(x);
> -  if(m == 0)
> -    return 0;
> +  m = m == 0.0f ? 1.0f : m;
>    return x / m;
>  }
>  OVERLOADABLE float4 normalize(float4 x) {
>    float m = length(x);
> -  if(m == 0)
> -    return 0;
> +  m = m == 0.0f ? 1.0f : m;
>    return x / m;
>  }
>  
> -- 
> 1.7.10.4
> 
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