[FFmpeg-devel] [PATCH 04/11] avcodec/zmbvenc: use log2 instead of log()/M_LN2

[Michael Niedermayer]

On Thu, Oct 29, 2015 at 12:20:02AM -0400, Ganesh Ajjanagadde wrote:
> This is likely more precise and conveys the intent better.
> 
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/zmbvenc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavcodec/zmbvenc.c b/libavcodec/zmbvenc.c
> index df06e37..e832bed 100644
> --- a/libavcodec/zmbvenc.c
> +++ b/libavcodec/zmbvenc.c
> @@ -277,7 +277,7 @@ static av_cold int encode_init(AVCodecContext *avctx)
>      int lvl = 9;
>  
>      for(i=1; i<256; i++)
> -        score_tab[i]= -i * log(i/(double)(ZMBV_BLOCK*ZMBV_BLOCK)) * (256/M_LN2);
> +        score_tab[i]= -i * log2(i/(double)(ZMBV_BLOCK*ZMBV_BLOCK)) * 256;

Interrestingly this changes the output from
ffmpeg -i matrixbench_mpeg2.mpg -vcodec zmbv -frames 30  -an -f framecrc -
for a few frames

the code change looks good though

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Rewriting code that is poorly written but fully understood is good.
Rewriting code that one doesnt understand is a sign that one is less smart
then the original author, trying to rewrite it will not make it better.
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