Re: [FFmpeg-devel] [PATCH 2/4] avcodec/vvc/dec: Don't use GetBit-API when byte-aligned

[Nuo Mi <nuomi2021-at-gmail.com@ffmpeg.org>]

LGTM for this.
Thank you, Andreas.

On Fri, Jul 4, 2025 at 9:45 PM Andreas Rheinhardt <
ffmpegagent-at-gmail.com@ffmpeg.org> wrote:

> From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/vvc/dec.c | 29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
>
> diff --git a/libavcodec/vvc/dec.c b/libavcodec/vvc/dec.c
> index 7930d64a05..90fff3a03f 100644
> --- a/libavcodec/vvc/dec.c
> +++ b/libavcodec/vvc/dec.c
> @@ -20,6 +20,8 @@
>   * License along with FFmpeg; if not, write to the Free Software
>   * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
> 02110-1301 USA
>   */
> +
> +#include "libavcodec/bytestream.h"
>  #include "libavcodec/codec_internal.h"
>  #include "libavcodec/decode.h"
>  #include "libavcodec/hwaccel_internal.h"
> @@ -509,13 +511,14 @@ static int slices_realloc(VVCFrameContext *fc)
>      return 0;
>  }
>
> -static int get_ep_size(const H266RawSliceHeader *rsh, GetBitContext *gb,
> const H2645NAL *nal, const int header_size, const int ep_index)
> +static int get_ep_size(const H266RawSliceHeader *rsh, const
> GetByteContext *gb,
> +                       const H2645NAL *nal, const int header_size, const
> int ep_index)
>  {
>      int size;
>
>      if (ep_index < rsh->num_entry_points) {
>          int skipped = 0;
> -        int64_t start =  (gb->index >> 3);
> +        int64_t start = bytestream2_tell(gb);
>          int64_t end = start + rsh->sh_entry_point_offset_minus1[ep_index]
> + 1;
>          while (skipped < nal->skipped_bytes &&
> nal->skipped_bytes_pos[skipped] <= start + header_size) {
>              skipped++;
> @@ -525,26 +528,27 @@ static int get_ep_size(const H266RawSliceHeader
> *rsh, GetBitContext *gb, const H
>              skipped++;
>          }
>          size = end - start;
> -        size = av_clip(size, 0, get_bits_left(gb) / 8);
> +        size = av_clip(size, 0, bytestream2_get_bytes_left(gb));
>      } else {
> -        size = get_bits_left(gb) / 8;
> +        size = bytestream2_get_bytes_left(gb);
>      }
>      return size;
>  }
>
> -static int ep_init_cabac_decoder(EntryPoint *ep, GetBitContext *gb, const
> int size)
> +static int ep_init_cabac_decoder(EntryPoint *ep, GetByteContext *gb,
> const int size)
>  {
>      int ret;
>
> -    av_assert0(gb->buffer + get_bits_count(gb) / 8 + size <=
> gb->buffer_end);
> -    ret = ff_init_cabac_decoder (&ep->cc, gb->buffer + get_bits_count(gb)
> / 8, size);
> +    av_assert0(size <= bytestream2_get_bytes_left(gb));
> +    ret = ff_init_cabac_decoder(&ep->cc, gb->buffer, size);
>      if (ret < 0)
>          return ret;
> -    skip_bits(gb, size * 8);
> +    bytestream2_skipu(gb, size);
>      return 0;
>  }
>
> -static int ep_init(EntryPoint *ep, const int ctu_addr, const int ctu_end,
> GetBitContext *gb, const int size)
> +static int ep_init(EntryPoint *ep, const int ctu_addr, const int ctu_end,
> +                   GetByteContext *gb, const int size)
>  {
>      const int ret = ep_init_cabac_decoder(ep, gb, size);
>
> @@ -567,7 +571,7 @@ static int slice_init_entry_points(SliceContext *sc,
>      const H266RawSlice *slice = unit->content_ref;
>      int nb_eps                = sh->r->num_entry_points + 1;
>      int ctu_addr              = 0;
> -    GetBitContext gb;
> +    GetByteContext gb;
>      int ret;
>
>      if (sc->nb_eps != nb_eps) {
> @@ -578,9 +582,8 @@ static int slice_init_entry_points(SliceContext *sc,
>          sc->nb_eps = nb_eps;
>      }
>
> -    ret = init_get_bits8(&gb, slice->data, slice->data_size);
> -    if (ret < 0)
> -        return ret;
> +    bytestream2_init(&gb, slice->data, slice->data_size);
> +
>      for (int i = 0; i < sc->nb_eps; i++)
>      {
>          const int size    = get_ep_size(sc->sh.r, &gb, nal,
> slice->header_size, i);
> --
> ffmpeg-codebot
>
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