[FFmpeg-devel] [PATCH] Use av_clip_uint8 in swscale.

[Michael Niedermayer]

On Sat, Aug 15, 2009 at 05:53:49PM +0100, M?ns Rullg?rd wrote:
> Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
> 
> > On Sat, Aug 15, 2009 at 12:27:49PM -0300, Ramiro Polla wrote:
> >> diff --git a/swscale.c b/swscale.c
> >> index c513066..340acfc 100644
> >> --- a/swscale.c
> >> +++ b/swscale.c
> >> @@ -688,21 +688,12 @@ static inline void yuv2nv12XinC(const int16_t *lumFilter, const int16_t **lumSrc
> >>  
> >>  #define YSCALE_YUV_2_PACKEDX_C(type,alpha) \
> >>          YSCALE_YUV_2_PACKEDX_NOCLIP_C(type,alpha)\
> >> -        if ((Y1|Y2|U|V)&256)\
> >> -        {\
> >> -            if (Y1>255)   Y1=255; \
> >> -            else if (Y1<0)Y1=0;   \
> >> -            if (Y2>255)   Y2=255; \
> >> -            else if (Y2<0)Y2=0;   \
> >> -            if (U>255)    U=255;  \
> >> -            else if (U<0) U=0;    \
> >> -            if (V>255)    V=255;  \
> >> -            else if (V<0) V=0;    \
> >> -        }\
> >> -        if (alpha && ((A1|A2)&256)){\
> >> -            A1=av_clip_uint8(A1);\
> >> -            A2=av_clip_uint8(A2);\
> >> -        }
> >> +        Y1 = av_clip_uint8(Y1); \
> >> +        Y2 = av_clip_uint8(Y2); \
> >> +        U  = av_clip_uint8(U ); \
> >> +        V  = av_clip_uint8(V ); \
> >> +        A1 = av_clip_uint8(A1); \
> >> +        A2 = av_clip_uint8(A2); \
> >
> > This
> >
> >> -            if ((u|v)&256){
> >> -                if (u<0)        u=0;
> >> -                else if (u>255) u=255;
> >> -                if (v<0)        v=0;
> >> -                else if (v>255) v=255;
> >> -            }
> >> -
> >> -            uDest[i]= u;
> >> -            vDest[i]= v;
> >> +            uDest[i]= av_clip_uint8((chrSrc[i       ]+64)>>7);
> >> +            vDest[i]= av_clip_uint8((chrSrc[i + VOFW]+64)>>7);
> >
> > And this need to be benchmarked (well, or at least have a look at the
> > generated code.
> > If clipping is very, very rare the original code might be faster.
> 
> Depends on hardware.  On processors with fast clipping instructions,
> always clipping is likely to be faster.

if they are fast enough, sure, but which cpu would that be?

besides which compiler would turn the pure C av_clip_uint8 into such
instructions ?


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

The educated differ from the uneducated as much as the living from the
dead. -- Aristotle 
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