Re: [FFmpeg-devel] [PATCH 3/4] avcodec/evc_parse: remove pow() and log2()

[Michael Niedermayer <michael@niedermayer.cc>]

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On Fri, Oct 27, 2023 at 10:15:49AM +0200, Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff Engineer/Samsung Electronics wrote:
> 
> 
> 
> 
> > -----Original Message-----
> > From: ffmpeg-devel <ffmpeg-devel-bounces@ffmpeg.org> On Behalf Of
> > Michael Niedermayer
> > Sent: czwartek, 5 października 2023 00:59
> > To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
> > Subject: [FFmpeg-devel] [PATCH 3/4] avcodec/evc_parse: remove pow() and
> > log2()
> > 
> > The use of float based functions is both unneeded and wrong due to
> > unpredictable rounding
> > 
> > Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
> > ---
> >  libavcodec/evc_parse.c | 10 ++++++----
> >  1 file changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/libavcodec/evc_parse.c b/libavcodec/evc_parse.c index
> > 5ab33166cf3..20b6849041a 100644
> > --- a/libavcodec/evc_parse.c
> > +++ b/libavcodec/evc_parse.c
> > @@ -176,7 +176,8 @@ int ff_evc_derive_poc(const EVCParamSets *ps, const
> > EVCParserSliceHeader *sh,
> >              poc->PicOrderCntVal = 0;
> >              poc->DocOffset = -1;
> >          } else {
> > -            int SubGopLength = (int)pow(2.0, sps->log2_sub_gop_length);
> > +            int SubGopLength = 1 << sps->log2_sub_gop_length;
> > +
> >              if (tid == 0) {
> >                  poc->PicOrderCntVal = poc->prevPicOrderCntVal +
> SubGopLength;
> >                  poc->DocOffset = 0;
> > @@ -191,15 +192,16 @@ int ff_evc_derive_poc(const EVCParamSets *ps, const
> > EVCParserSliceHeader *sh,
> >                      poc->prevPicOrderCntVal += SubGopLength;
> >                      ExpectedTemporalId = 0;
> >                  } else
> > -                    ExpectedTemporalId = 1 + (int)log2(poc->DocOffset);
> > +                    ExpectedTemporalId = 1 + av_log2(poc->DocOffset);
> > +
> >                  while (tid != ExpectedTemporalId) {
> >                      poc->DocOffset = (poc->DocOffset + 1) % SubGopLength;
> >                      if (poc->DocOffset == 0)
> >                          ExpectedTemporalId = 0;
> >                      else
> > -                        ExpectedTemporalId = 1 +
> (int)log2(poc->DocOffset);
> > +                        ExpectedTemporalId = 1 +
> > + av_log2(poc->DocOffset);
> >                  }
> > -                PocOffset = (int)(SubGopLength * ((2.0 * poc->DocOffset +
> 1) /
> > (int)pow(2.0, tid) - 2));
> > +                PocOffset = (int)(SubGopLength * ((2.0 * poc->DocOffset
> > + + 1) / (1 << tid) - 2));
> >                  poc->PicOrderCntVal = poc->prevPicOrderCntVal +
> PocOffset;
> >              }
> >          }
> > --
> > 2.17.1
> > 
> Reviewed. Looks good. It can be merged.

will apply

thx

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

It is what and why we do it that matters, not just one of them.

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