[FFmpeg-devel] [PATCH] cbs_mpeg2_split_fragment(): cache the buffer end

[Scott Theisen]

Ping; it still applies cleanly.

-Scott Theisen

On 2/8/22 15:32, Scott Theisen wrote:
> Also add a few clarifying comments.
> ---
>   libavcodec/cbs_mpeg2.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
> index 33bd3e0998..47732562d1 100644
> --- a/libavcodec/cbs_mpeg2.c
> +++ b/libavcodec/cbs_mpeg2.c
> @@ -144,12 +144,12 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
>                                       CodedBitstreamFragment *frag,
>                                       int header)
>   {
> -    const uint8_t *start;
> +    const uint8_t *start = frag->data;
> +    const uint8_t * const buf_end = frag->data + frag->data_size;
>       uint32_t start_code = -1;
>       int err;
>   
> -    start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
> -                                   &start_code);
> +    start = avpriv_find_start_code(start, buf_end, &start_code);
>       if (start_code >> 8 != 0x000001) {
>           // No start code found.
>           return AVERROR_INVALIDDATA;
> @@ -165,12 +165,11 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
>           // start code in any way (as e.g. happens when there is a
>           // Sequence End unit at the very end of a packet).
>           start_code = UINT32_MAX;
> -        end = avpriv_find_start_code(start--, frag->data + frag->data_size,
> -                                     &start_code);
> -
> -        // start points to the byte containing the start_code_identifier
> +        end = avpriv_find_start_code(start, buf_end, &start_code);
> +        start--;
> +        // decrement so start points to the byte containing the start_code_identifier
>           // (may be the last byte of fragment->data); end points to the byte
> -        // following the byte containing the start code identifier (or to
> +        // following the byte containing the next start code identifier (or to
>           // the end of fragment->data).
>           if (start_code >> 8 == 0x000001) {
>               // Unit runs from start to the beginning of the start code
> @@ -178,6 +177,7 @@ static int cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
>               unit_size = (end - 4) - start;
>           } else {
>              // We didn't find a start code, so this is the final unit.
> +           // There is no start code to remove from end, hence not (end - 4).
>              unit_size = end - start;
>           }
>