Re: [FFmpeg-devel] [PATCH 04/11] avcodec/zmbvenc: use log2 instead of log()/M_LN2
On Thu, Oct 29, 2015 at 9:25 AM, Michael Niedermayer wrote: > 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 >> --- >> 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 not too surprising, there are bit changes for many inputs when one moves from log/ to log2 etc. See e.g my reply to wm4's original comments. > > the code change looks good though pushed, thanks. > > [...] > -- > 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. > > ___ > ffmpeg-devel mailing list > ffmpeg-devel@ffmpeg.org > http://ffmpeg.org/mailman/listinfo/ffmpeg-devel > ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH 04/11] avcodec/zmbvenc: use log2 instead of log()/M_LN2
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 > --- > 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. signature.asc Description: Digital signature ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
[FFmpeg-devel] [PATCH 04/11] avcodec/zmbvenc: use log2 instead of log()/M_LN2
This is likely more precise and conveys the intent better. Signed-off-by: Ganesh Ajjanagadde --- 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; c->avctx = avctx; -- 2.6.2 ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
