[FFmpeg-devel] [PATCH 5/7] get_bits: improve and fix get_bits_long for 32b

[Michael Niedermayer]

On Tue, Apr 14, 2020 at 10:25:01AM +0000, Christophe Gisquet wrote:
> The new code is guaranteed to read at least 32bits, which is likely ok with
> the usual case that get_bits without cache can read up to 25.
> ---
>  libavcodec/get_bits.h | 29 ++++++++++++++++++++++++++---
>  1 file changed, 26 insertions(+), 3 deletions(-)
> 
> diff --git a/libavcodec/get_bits.h b/libavcodec/get_bits.h
> index 4f75f9dd84..da054ebfcb 100644
> --- a/libavcodec/get_bits.h
> +++ b/libavcodec/get_bits.h
> @@ -608,21 +608,44 @@ static inline void skip_bits1(GetBitContext *s)
>   */
>  static inline unsigned int get_bits_long(GetBitContext *s, int n)
>  {
> +    unsigned ret = 0;

Dead assignment if CACHED_BITSTREAM_READER is not used


>      av_assert2(n>=0 && n<=32);
>      if (!n) {
>          return 0;
>  #if CACHED_BITSTREAM_READER
>      }
> -    return get_bits(s, n);
> +
> +# ifdef BITSTREAM_READER_LE
> +    unsigned left = 0;
> +# endif
> +    if (n > s->bits_left) {
> +        n -= s->bits_left;

> +# ifdef BITSTREAM_READER_LE
> +        left = s->bits_left;
> +        ret = get_val(s, s->bits_left, 1);
> +        refill_all(s, 1);
> +# else
> +        ret = get_val(s, s->bits_left, 0);
> +        refill_all(s, 0);
> +# endif

Its a pitty one cannot write the following

+# ifdef BITSTREAM_READER_LE
+        left = s->bits_left;
+# endif
+        ret = get_val(s, s->bits_left, BITSTREAM_READER_LE);
+        refill_all(s, BITSTREAM_READER_LE);

that would be nicer looking if it worked


[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: not available
URL: <https://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20200414/21e6a8b5/attachment.sig>