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

[Måns Rullgård]

Michael Niedermayer <michaelni at gmx.at> writes:

> 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?

ARM and AVR32 to name two.

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

We could write an asm version of it.

-- 
M?ns Rullg?rd
mans at mansr.com