[FFmpeg-devel] [PATCH] lavu/frame: Optimize frame_copy_video

[Michael Niedermayer]

On Mon, Dec 14, 2015 at 07:36:51PM +0100, Jean Delvare wrote:
> As I understand it, the temporary stack buffer "src_data" was
> introduced solely to avoid a compiler warning. I believe that a better
> way to solve this warning it to explicitly cast src->data. This
> should be somewhat faster, and just as safe.
> 
> Signed-off-by: Jean Delvare <jdelvare at suse.de>
> Cc: Anton Khirnov <anton at khirnov.net>
> ---
>  libavutil/frame.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> --- ffmpeg.orig/libavutil/frame.c	2015-12-14 18:42:06.272234579 +0100
> +++ ffmpeg/libavutil/frame.c	2015-12-14 19:05:18.501745387 +0100
> @@ -647,7 +647,6 @@ AVFrameSideData *av_frame_get_side_data(
>  
>  static int frame_copy_video(AVFrame *dst, const AVFrame *src)
>  {
> -    const uint8_t *src_data[4];
>      int i, planes;
>  
>      if (dst->width  < src->width ||
> @@ -659,9 +658,8 @@ static int frame_copy_video(AVFrame *dst
>          if (!dst->data[i] || !src->data[i])
>              return AVERROR(EINVAL);
>  
> -    memcpy(src_data, src->data, sizeof(src_data));
>      av_image_copy(dst->data, dst->linesize,
> -                  src_data, src->linesize,
> +                  (const uint8_t **)src->data, src->linesize,

I think this may be a aliasing violation and thus undefined
not that i like that or consider that sane
so if someone says iam wrong, i would certainly not be unhappy

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

I have never wished to cater to the crowd; for what I know they do not
approve, and what they approve I do not know. -- Epicurus
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