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

[Reimar Döffinger]

On 30.08.2014, at 18:29, Reimar Döffinger <Reimar.Doeffinger at gmx.de> wrote:
> 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?

Just to be clear since it's not obvious: the lines just below what I added initialise the second half of the array.
I just added that the first half is initialised in the same place.