Re: [FFmpeg-devel] [PATCH] avcodec/on2avc: Fix stability issues with scale_tab generation
On Sun, Dec 27, 2015 at 7:44 AM, Michael Niedermayer wrote: > On Sun, Dec 27, 2015 at 07:40:53AM -0500, Ronald S. Bultje wrote: >> Hi, >> >> On Sun, Dec 27, 2015 at 6:02 AM, Michael Niedermayer >> wrote: >> >> > +for (i = 0; i < 20; i++) >> > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 16 - 0.01) / 32; >> > for (; i < 128; i++) >> > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 0.5 - 0.01); >> > >> >> To innocent bystanders, this is hard to understand. Let's keep it a habit >> to document things (what and why), where the "what" portion is probably >> "this code emulates pow(10, x) with ff_pow10(x - 0.01)". As for why (most >> specifically, why the 0.01?), I'm going to assume that here, you're trying >> to get unit integers to not go to unit.000[..]001, so you subtract 0.01 >> before the ceil so it works fine again to get the exact unit integer output >> number. If that's correct, please add a comment saying that, and then lgtm. In my view this change is not good for the exact reasons above. It is a "magic constant" that is a pure hack. The commit I made made accuracy more consistent across platforms (instead of relying on the whims of libm's pow/exp2), and was commented so that intent was clear. Nack from me. > > yes > changed > applied > thx > > > [...] > -- > Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB > > Concerning the gods, I have no means of knowing whether they exist or not > or of what sort they may be, because of the obscurity of the subject, and > the brevity of human life -- Protagoras > > ___ > 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] avcodec/on2avc: Fix stability issues with scale_tab generation
On Sun, Dec 27, 2015 at 07:40:53AM -0500, Ronald S. Bultje wrote: > Hi, > > On Sun, Dec 27, 2015 at 6:02 AM, Michael Niedermayer > wrote: > > > +for (i = 0; i < 20; i++) > > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 16 - 0.01) / 32; > > for (; i < 128; i++) > > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 0.5 - 0.01); > > > > To innocent bystanders, this is hard to understand. Let's keep it a habit > to document things (what and why), where the "what" portion is probably > "this code emulates pow(10, x) with ff_pow10(x - 0.01)". As for why (most > specifically, why the 0.01?), I'm going to assume that here, you're trying > to get unit integers to not go to unit.000[..]001, so you subtract 0.01 > before the ceil so it works fine again to get the exact unit integer output > number. If that's correct, please add a comment saying that, and then lgtm. yes changed applied thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Concerning the gods, I have no means of knowing whether they exist or not or of what sort they may be, because of the obscurity of the subject, and the brevity of human life -- Protagoras signature.asc Description: Digital signature ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
Re: [FFmpeg-devel] [PATCH] avcodec/on2avc: Fix stability issues with scale_tab generation
Hi, On Sun, Dec 27, 2015 at 6:02 AM, Michael Niedermayer wrote: > +for (i = 0; i < 20; i++) > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 16 - 0.01) / 32; > for (; i < 128; i++) > +c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 0.5 - 0.01); > To innocent bystanders, this is hard to understand. Let's keep it a habit to document things (what and why), where the "what" portion is probably "this code emulates pow(10, x) with ff_pow10(x - 0.01)". As for why (most specifically, why the 0.01?), I'm going to assume that here, you're trying to get unit integers to not go to unit.000[..]001, so you subtract 0.01 before the ceil so it works fine again to get the exact unit integer output number. If that's correct, please add a comment saying that, and then lgtm. Ronald ___ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
