[FFmpeg-soc] [soc]: r3871 - dirac/libavcodec/diracdec.c

[David Conrad]

On Dec 6, 2008, at 6:21 AM, Michael Niedermayer wrote:

> On Sat, Dec 06, 2008 at 03:01:00AM +0100, conrad wrote:
>> Author: conrad
>> Date: Sat Dec  6 03:00:59 2008
>> New Revision: 3871
>>
>> Log:
>> Small optimization
>>
>>
>> Modified:
>>   dirac/libavcodec/diracdec.c
>>
>> Modified: dirac/libavcodec/diracdec.c
>> =
>> =
>> =
>> =
>> =
>> =
>> =
>> =
>> =
>> =====================================================================
>> --- dirac/libavcodec/diracdec.c	(original)
>> +++ dirac/libavcodec/diracdec.c	Sat Dec  6 03:00:59 2008
>> @@ -664,9 +664,9 @@ static int dirac_decode_frame_internal(D
>>             mcline    = s->mcpic;
>>             for (y = 0; y < height; y++) {
>>                 for (x = 0; x < width; x++) {
>> +                    int coeff = mcline[x] + (1 << (s- 
>> >total_wt_bits - 1));
>> +                    coeff = line[x] + (coeff >> s->total_wt_bits);
>> +                    frame[x]= av_clip_uint8(coeff + 128);
>>                 }
>
> depending on how large total_wt_bits can be, the following might be  
> possible
>
> bias= 257 << (s->total_wt_bits - 1);
> for (y = 0; y < height; y++) {
>    for (x = 0; x < width; x++) {
>        int coeff = mcline[x] + bias;
>        coeff = line[x] + (coeff >> s->total_wt_bits);
>        frame[x]= av_clip_uint8(coeff);
>    }
> }

I don't think the spec limits how large total_wt_bits can be, but  
commonly it's not more than 7 and can't exceed 22 without using  
macroblocks with width or height greater than 1023, so this should be  
safe for sane files.