[FFmpeg-devel] [PATCH] mpeg2: fix block_last_index when mismatch control modifies last coeff

[Michael Niedermayer]

On Sun, Jun 20, 2010 at 11:41:32PM +0100, Mans Rullgard wrote:
> ---
>  libavcodec/mpeg12.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/mpeg12.c b/libavcodec/mpeg12.c
> index bc9ddcc..bd579ac 100644
> --- a/libavcodec/mpeg12.c
> +++ b/libavcodec/mpeg12.c
> @@ -939,7 +939,7 @@ end:
>      }
>      block[63] ^= (mismatch & 1);
>  
> -    s->block_last_index[n] = i;
> +    s->block_last_index[n] = block[63]? 63: i;
>      return 0;
>  }
>  
> @@ -1090,7 +1090,7 @@ static inline int mpeg2_decode_block_intra(MpegEncContext *s,
>      }
>      block[63]^= mismatch&1;
>  
> -    s->block_last_index[n] = i;
> +    s->block_last_index[n] = block[63]? 63: i;
>      return 0;

is this fixing a bug?
because, if it makes no difference, then it would cause a speedloss
and possibly not small if this is a conditional branch that fails to be
predicted

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

I am the wisest man alive, for I know one thing, and that is that I know
nothing. -- Socrates
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