[FFmpeg-devel] [PATCH] cabac: initialize all of ff_h264_cabac_tables programmatically.

[Reimar Döffinger]

On Sat, Aug 30, 2014 at 06:20:56PM +0200, wm4 wrote:
> On Sat, 30 Aug 2014 18:18:41 +0200
> Reimar Döffinger <Reimar.Doeffinger at gmx.de> wrote:
> 
> > Moves it from .data to .bss, slightly reducing binary size.
> > 
> > Signed-off-by: Reimar Döffinger <Reimar.Doeffinger at gmx.de>
> > ---
> >  libavcodec/cabac.c | 26 ++++----------------------
> >  1 file changed, 4 insertions(+), 22 deletions(-)
> > 
> > diff --git a/libavcodec/cabac.c b/libavcodec/cabac.c
> > index 65579d8..803c81c 100644
> > --- a/libavcodec/cabac.c
> > +++ b/libavcodec/cabac.c
> > @@ -32,28 +32,7 @@
> >  #include "cabac.h"
> >  #include "cabac_functions.h"
> >  
> > -uint8_t ff_h264_cabac_tables[512 + 4*2*64 + 4*64 + 63] = {
> > - 9,8,7,7,6,6,6,6,5,5,5,5,5,5,5,5,
> > - 4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
> > - 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> > - 3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,3,
> > - 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
> > - 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
> > - 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
> > - 2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,
> > - 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> > - 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> > - 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> > - 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > - 0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
> > -};
> > +uint8_t ff_h264_cabac_tables[512 + 4*2*64 + 4*64 + 63];
> >  
> >  static const uint8_t lps_range[64][4]= {
> >  {128,176,208,240}, {128,167,197,227}, {128,158,187,216}, {123,150,178,205},
> > @@ -143,6 +122,9 @@ void ff_init_cabac_states(void)
> >      if (initialized)
> >          return;
> >  
> > +    for (i = 0; i < 512; i++)
> > +        ff_h264_norm_shift[i] = i ? 8 - av_log2(i) : 9;
> > +
> >      for(i=0; i<64; i++){
> >          for(j=0; j<4; j++){ //FIXME check if this is worth the 1 shift we save
> >              ff_h264_lps_range[j*2*64+2*i+0]=
> 
> Doesn't this make library safety issues worse, instead of improving it?

Why would it make anything even a slightest bit worse than it is now?
Also, it makes it easier to make this hardcoded, which I think solves
your concern?