Anton Khirnov:
> Also rename it to bitstream_skip_cache(), which is more descriptive and
> follows the naming conventions of tis API.
> ---
> libavcodec/bitstream.h | 1 +
> libavcodec/bitstream_template.h | 19 ++++++++++++-------
> 2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/libavcodec/bitstream.h b/libavcodec/bitstream.h
> index 3fa63695d3..364245453b 100644
> --- a/libavcodec/bitstream.h
> +++ b/libavcodec/bitstream.h
> @@ -116,6 +116,7 @@ static inline void bitstream_unget(BitstreamContext *bc,
> uint64_t value,
> #define bitstream_peek bitstream_peek_be
> #define bitstream_peek_signed bitstream_peek_signed_be
> #define bitstream_skip bitstream_skip_be
> +#define bitstream_skip_cache bitstream_skip_cache_be
> #define bitstream_seek bitstream_seek_be
> #define bitstream_align bitstream_align_be
> #define bitstream_read_xbits bitstream_read_xbits_be
> diff --git a/libavcodec/bitstream_template.h b/libavcodec/bitstream_template.h
> index 14a420139c..717473ca40 100644
> --- a/libavcodec/bitstream_template.h
> +++ b/libavcodec/bitstream_template.h
> @@ -225,7 +225,12 @@ static inline int
> BS_FUNC(bitstream_peek_signed)(BitstreamContext *bc, unsigned
> return sign_extend(BS_FUNC(bitstream_peek)(bc, n), n);
> }
>
> -static inline void BS_FUNC(skip_remaining)(BitstreamContext *bc, unsigned
> int n)
> +/**
> + * Skip n bits from the cache. This may only be called if at least n bits are
> + * guaranteed to be in the cache, e.g. right after bitstream_peek(n).
> + * Otherwise use bitstream_skip().
> + */
> +static inline void BS_FUNC(bitstream_skip_cache)(BitstreamContext *bc,
> unsigned int n)
> {
> #ifdef BITSTREAM_LE
> bc->bits >>= n;
> @@ -241,7 +246,7 @@ static inline void
> BS_FUNC(skip_remaining)(BitstreamContext *bc, unsigned int n)
> static inline void BS_FUNC(bitstream_skip)(BitstreamContext *bc, unsigned
> int n)
> {
> if (n < bc->bits_left)
> - BS_FUNC(skip_remaining)(bc, n);
> + BS_FUNC(bitstream_skip_cache)(bc, n);
> else {
> n -= bc->bits_left;
> bc->bits = 0;
> @@ -255,7 +260,7 @@ static inline void
> BS_FUNC(bitstream_skip)(BitstreamContext *bc, unsigned int n)
> }
> BS_FUNC(refill_64)(bc);
> if (n)
> - BS_FUNC(skip_remaining)(bc, n);
> + BS_FUNC(bitstream_skip_cache)(bc, n);
> }
> }
>
> @@ -291,7 +296,7 @@ static inline int
> BS_FUNC(bitstream_read_xbits)(BitstreamContext *bc, unsigned i
> {
> int32_t cache = BS_FUNC(bitstream_peek)(bc, 32);
> int sign = ~cache >> 31;
> - BS_FUNC(skip_remaining)(bc, n);
> + BS_FUNC(bitstream_skip_cache)(bc, n);
>
> return ((((uint32_t)(sign ^ cache)) >> (32 - n)) ^ sign) - sign;
> }
> @@ -374,14 +379,14 @@ static inline int
> BS_FUNC(bitstream_read_vlc)(BitstreamContext *bc, VLC_TYPE (*t
> int n = table[idx][1];
>
> if (max_depth > 1 && n < 0) {
> - BS_FUNC(skip_remaining)(bc, bits);
> + BS_FUNC(bitstream_skip_cache)(bc, bits);
> code = BS_FUNC(set_idx)(bc, code, &n, &nb_bits, table);
> if (max_depth > 2 && n < 0) {
> - BS_FUNC(skip_remaining)(bc, nb_bits);
> + BS_FUNC(bitstream_skip_cache)(bc, nb_bits);
> code = BS_FUNC(set_idx)(bc, code, &n, &nb_bits, table);
> }
> }
> - BS_FUNC(skip_remaining)(bc, n);
> + BS_FUNC(bitstream_skip_cache)(bc, n);
>
> return code;
> }
How do you intend to avoid the issue described here:
https://ffmpeg.org/pipermail/ffmpeg-devel/2022-June/297850.html?
Bitstream_peek() does not guarantee that there are bits bits in the
cache even though your documentation says otherwise.
- Andreas
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