[FFmpeg-devel] [PATCH 2/4] lavc/mpegvideo: use H263DSP dequant function

[Rémi Denis-Courmont]

Le lauantaina 6. heinäkuuta 2024, 18.23.00 EEST Andreas Rheinhardt a écrit :
> >  static void dct_unquantize_h263_inter_c(MpegEncContext *s,
> >  
> >                                    int16_t *block, int n, int qscale)
> >  
> >  {
> > 
> > -    int i, level, qmul, qadd;
> > +    int qmul = qscale << 1;
> > +    int qadd = (qscale - 1) | 1;
> > 
> >      int nCoeffs;
> >      
> >      av_assert2(s->block_last_index[n]>=0);
> > 
> > -    qadd = (qscale - 1) | 1;
> > -    qmul = qscale << 1;
> > -
> > 
> >      nCoeffs= s->inter_scantable.raster_end[ s->block_last_index[n] ];
> > 
> > -
> > -    for(i=0; i<=nCoeffs; i++) {
> > -        level = block[i];
> > -        if (level) {
> > -            if (level < 0) {
> > -                level = level * qmul - qadd;
> > -            } else {
> > -                level = level * qmul + qadd;
> > -            }
> > -            block[i] = level;
> > -        }
> > -    }
> > +    s->h263dsp.h263_dct_unquantize_inter(block, nCoeffs, qmul, qadd);
> 
> This adds an indirection. I have asked you to actually benchmark this
> code (and not only the DSP function you add), but you never did.

I already pointed out previously that this is the way this project does DSP 
code. Certainly it would be nice to hard-code the path when there is only one 
possible. This is often the case on Armv8 notably, and of course on platforms 
without optimisations.

But that's a general problem way beyond the scope of this patchset. We always 
add indirect function calls in this sort of situation, and I don't see why I 
would have duty to benchmark it, so I am going to ignore this.

-- 
雷米‧德尼-库尔蒙
http://www.remlab.net/