[FFmpeg-devel] [PATCH 1/4] lavc/h263dsp: add DCT dequantisation functions

[Rémi Denis-Courmont]

Le lauantaina 6. heinäkuuta 2024, 18.17.37 EEST Andreas Rheinhardt a écrit :
> Rémi Denis-Courmont:
> > Note that optimised implementations of these functions will be taken
> > into actual use only if MpegEncContext.dct_unquantize_h263_{inter,intra}
> > are *not* overloaded by existing optimisations.
> > ---
> > 
> >  libavcodec/h263dsp.c | 25 +++++++++++++++++++++++++
> >  libavcodec/h263dsp.h |  4 ++++
> >  2 files changed, 29 insertions(+)
> > 
> > diff --git a/libavcodec/h263dsp.c b/libavcodec/h263dsp.c
> > index 6a13353499..dc146bf821 100644
> > --- a/libavcodec/h263dsp.c
> > +++ b/libavcodec/h263dsp.c
> > @@ -19,10 +19,33 @@
> > 
> >  #include <stdint.h>
> >  
> >  #include "libavutil/attributes.h"
> > 
> > +#include "libavutil/avassert.h"
> > 
> >  #include "libavutil/common.h"
> >  #include "config.h"
> >  #include "h263dsp.h"
> > 
> > +static void h263_dct_unquantize_inter_c(int16_t *block, ptrdiff_t len,
> > +                                        int qmul, int qadd)
> > +{
> > +    for (ptrdiff_t i = 0; i <= len; i++) {
> 
> In the current code, the unquantizing inter does not need an initial
> check (the compiler can optimize the for-loop to a do-while-like loop).
> This will be lost here.

If this not the consequence of your own actions...

You asked:
- to use a signed type there, and
- to avoid the separate initial branch in the intra case.

And that is exactly how this ends up. You can't have it both ways.

-- 
レミ・デニ-クールモン
http://www.remlab.net/