On Tue, Jul 14, 2020 at 11:14:19PM +0200, Andreas Rheinhardt wrote: > Michael Niedermayer: > > On Tue, Jul 14, 2020 at 10:43:51PM +0200, Andreas Rheinhardt wrote: > >> Michael Niedermayer: > >>> On Tue, Jul 14, 2020 at 05:34:50PM +0200, Andreas Rheinhardt wrote: > >>>> get_ue_golomb_31() uses a LUT of 512 entries; therefore it can be used > >>>> to parse exp-golomb codes of length <= 9, i.e. those codes with at most > >>>> four leading bits that have five effective bits; this implies a range of > >>>> 0..30 and not 31. In particular, this function must not be used to parse > >>>> e.g. the H.264 SPS id. > >>> > >>> hmm, are you sure ? > >>> > >> > >> Yes. > >> > >>> 1 0 > >>> 01X 1-2 > >>> 001XX 3-6 > >>> 0001XXX 7-14 > >>> 00001XXXX 15-30 > >>> 000001..... 31 > >>> > >>> we need to read 9 bits for this, we do not need to read the bits marked > >>> with > >>> a "." because the code is already determined at this point. > >>> > >> The code is only determined at the point if one already presumes that it > >> can't be anything >31. > > > > yes, that is the idea of get_ue_golomb_31() its only used when the biggest > > valid code is 31. > > > But then we still have to rely on the code being valid as we have no way > to distinguish 31 from 32-34. Is this considered acceptable for the > speed gain?
Is it a problem when 32-34 (which are invalid) are mapped to 31 ? thx [...] -- Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB Asymptotically faster algorithms should always be preferred if you have asymptotical amounts of data
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