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

[Dawid Kozinski/Multimedia (PLT) /SRPOL/Staff Engineer/Samsung Electronics]

> -----Original Message-----
> From: ffmpeg-devel <ffmpeg-devel-boun...@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 <mich...@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.
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