Scott Theisen:
> ff_cbs_insert_unit_data() does not modify the data or data_size fields of
> the CodedBitstreamFragment. It also does not modify the value pointed to
> by start. (We don't need that byte in this function anymore, anyway.)
> ---
> libavcodec/cbs_mpeg2.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/libavcodec/cbs_mpeg2.c b/libavcodec/cbs_mpeg2.c
> index afe78eef9a..f2efedde5d 100644
> --- a/libavcodec/cbs_mpeg2.c
> +++ b/libavcodec/cbs_mpeg2.c
> @@ -144,23 +144,24 @@ static int
> cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
> CodedBitstreamFragment *frag,
> int header)
> {
> - const uint8_t *start, *end;
> + const uint8_t *start = frag->data, *end;
> + const uint8_t * const buf_end = frag->data + frag->data_size;
> CodedBitstreamUnitType unit_type;
> uint32_t start_code = -1;
> size_t unit_size;
> - int err, i = 0, final = 0;
> + int err, final = 0;
> + int i = -1; // offset for pre-increment
Using a pre-increment is unnatural (i is supposed to be the number of
units of the fragment and so it should naturally be incremented after a
unit has been successfully added to the fragment) and impairs clarity.
>
> - start = avpriv_find_start_code(frag->data, frag->data + frag->data_size,
> - &start_code, 1);
> + start = avpriv_find_start_code(start, buf_end, &start_code, 1);
> if (!avpriv_start_code_is_valid(start_code)) {
> // No start code found.
> return AVERROR_INVALIDDATA;
> }
>
> - while (!final) {
> + do {
> unit_type = start_code & 0xff;
>
> - if (start == frag->data + frag->data_size) {
> + if (start == buf_end) {
> // The last four bytes form a start code which constitutes
> // a unit of its own. In this situation avpriv_find_start_code
> // won't modify start_code at all so modify start_code so that
> @@ -168,10 +169,9 @@ static int
> cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
> start_code = 0;
> }
>
> - end = avpriv_find_start_code(start--, frag->data + frag->data_size,
> - &start_code, 0);
> -
> - // start points to the byte containing the start_code_identifier
> + end = avpriv_find_start_code(start, buf_end, &start_code, 0);
> + 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
> // the end of fragment->data).
> @@ -185,14 +185,14 @@ static int
> cbs_mpeg2_split_fragment(CodedBitstreamContext *ctx,
> final = 1;
> }
>
> - err = ff_cbs_insert_unit_data(frag, i, unit_type, (uint8_t*)start,
> + err = ff_cbs_insert_unit_data(frag, ++i, unit_type,
> + (uint8_t*)start /* cast away the const
> to match parameter type */,
redundant comment
> unit_size, frag->data_ref);
> if (err < 0)
> return err;
>
> start = end;
> - i++;
> - }
> + } while (!final);
>
> return 0;
> }
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