[FFmpeg-devel] [PATCH 1/2] avcodec/sheervideo: Improve creating VLC tables

[Paul B Mahol]

On Sat, Oct 10, 2020 at 06:57:03AM +0200, Andreas Rheinhardt wrote:
> Don't needlessly copy an array around; don't create a table with
> default symbols; and use smaller types to save stack space: The longest
> code here is 16 bits, so one can store the codes in this type.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
> ---
>  libavcodec/sheervideo.c | 19 +++++++------------
>  1 file changed, 7 insertions(+), 12 deletions(-)
> 

probably fine

> diff --git a/libavcodec/sheervideo.c b/libavcodec/sheervideo.c
> index ba9aecbb11..3f9b299a1e 100644
> --- a/libavcodec/sheervideo.c
> +++ b/libavcodec/sheervideo.c
> @@ -1782,25 +1782,20 @@ static void decode_rgb(AVCodecContext *avctx, AVFrame *p, GetBitContext *gb)
>  
>  static int build_vlc(VLC *vlc, const uint8_t *len, int count)
>  {
> -    uint32_t codes[1024];
> -    uint8_t bits[1024];
> -    uint16_t syms[1024];
> -    uint64_t index;
> +    uint16_t codes[1024];
> +    unsigned index;
>      int i;
>  
>      index = 0;
>      for (i = 0; i < count; i++) {
> -        codes[i]  = index >> (32 - len[i]);
> -        bits[i] = len[i];
> -        syms[i]  = i;
> -        index += 1ULL << (32 - len[i]);
> +        codes[i] = index >> (32 - len[i]);
> +        index   += 1U    << (32 - len[i]);
>      }
>  
>      ff_free_vlc(vlc);
> -    return ff_init_vlc_sparse(vlc, 12, count,
> -                              bits,  sizeof(*bits),  sizeof(*bits),
> -                              codes, sizeof(*codes), sizeof(*codes),
> -                              syms,  sizeof(*syms),  sizeof(*syms), 0);
> +    return init_vlc(vlc, 12, count,
> +                    len,   sizeof(*len),   sizeof(*len),
> +                    codes, sizeof(*codes), sizeof(*codes), 0);
>  }
>  
>  static int decode_frame(AVCodecContext *avctx,
> -- 
> 2.25.1
> 
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