[FFmpeg-devel] [PATCH 02/15] bytestream: Make get_bytes_left compatible with overread

[James Almer]

On 10/17/2019 5:29 AM, Andreas Rheinhardt wrote:
> bytestream2_get_bytes_left returns an unsigned int; as a result,
> it returns big positive numbers if an overread already happened,
> making it unsuitable for scenarios where one wants to allow this
> (because the buffer is actually padded so that no segfaults can
> happen). So add a function returning ptrdiff_t for this purpose;
> given that it is intended to be used with the unsafe functions,
> it has an "u" suffix, although it is not unsafe by itself.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavcodec/bytestream.h | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/libavcodec/bytestream.h b/libavcodec/bytestream.h
> index 7be7fc22fc..18774524cf 100644
> --- a/libavcodec/bytestream.h
> +++ b/libavcodec/bytestream.h
> @@ -156,6 +156,11 @@ static av_always_inline unsigned int bytestream2_get_bytes_left(GetByteContext *
>      return g->buffer_end - g->buffer;
>  }
>  
> +static av_always_inline ptrdiff_t bytestream2_get_bytes_leftu(GetByteContext *g)
> +{
> +    return g->buffer_end - g->buffer;
> +}

Just make bytestream2_get_bytes_left() return an int instead. It's what
get_bits_left() does, and it's used to detect overreads.
There's no need for a new function.

> +
>  static av_always_inline unsigned int bytestream2_get_bytes_left_p(PutByteContext *p)
>  {
>      return p->buffer_end - p->buffer;
>