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

[Yang, Rong R]

> -----Original Message-----
> From: Beignet [mailto:beignet-bounces at lists.freedesktop.org] On Behalf Of
> Zhigang Gong
> Sent: Thursday, January 29, 2015 16:25
> To: Song, Ruiling
> Cc: beignet at lists.freedesktop.org
> Subject: Re: [Beignet] [PATCH] libocl: refine implementation of normalize().
> 
> 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?
> 
[Yang, Rong R] How about :
float2 t = m == 0.0f ? x : x/m;
return t;

> 
> >  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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