[FFmpeg-devel] [PATCH 4/4] avcodec/pngdec: use memcpy instead of byte loops for P frames.

[Benoit Fouet]

Hi,

Le 03/12/2014 14:31, Benoit Fouet a écrit :
> Rely on the way memcpy is optimized for one's system instead of looping
> on a byte buffer for buffer copies to handle P frames.
> ---
>   libavcodec/pngdec.c | 25 +++++++++++++------------
>   1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/libavcodec/pngdec.c b/libavcodec/pngdec.c
> index 7e7b285..e6b7593 100644
> --- a/libavcodec/pngdec.c
> +++ b/libavcodec/pngdec.c
> @@ -884,8 +884,7 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
>           ff_thread_await_progress(&s->previous_picture, INT_MAX, 0);
>   
>       for (j = 0; j < s->y_offset; j++) {
> -        for (i = 0; i < ls; i++)
> -            pd[i] = pd_last[i];
> +        memcpy(pd, pd_last, ls);
>           pd      += s->image_linesize;
>           pd_last += s->image_linesize;
>       }
> @@ -907,8 +906,9 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
>           }
>   
>           for (j = s->y_offset; j < s->y_offset + s->cur_h; j++) {
> -            for (i = 0; i < s->x_offset * s->bpp; i++)
> -                pd[i] = pd_last[i];
> +            i = s->x_offset * s->bpp;
> +            if (i)
> +                memcpy(pd, pd_last, i);
>               for (; i < (s->x_offset + s->cur_w) * s->bpp; i += s->bpp) {
>                   uint8_t alpha = pd[i+ai];
>   
> @@ -930,26 +930,27 @@ static int handle_p_frame_apng(AVCodecContext *avctx, PNGDecContext *s,
>                       break;
>                   }
>               }
> -            for (; i < ls; i++)
> -                pd[i] = pd_last[i];
> +            if (ls - i)
> +                memcpy(pd+i, pd_last+i, ls - i);
>               pd      += s->image_linesize;
>               pd_last += s->image_linesize;
>               pd_last_region += s->image_linesize;
>           }
>       } else {
>           for (j = s->y_offset; j < s->y_offset + s->cur_h; j++) {
> -            for (i = 0; i < s->x_offset * s->bpp; i++)
> -                pd[i] = pd_last[i];
> -            for (i = (s->x_offset + s->cur_w) * s->bpp; i < ls; i++)
> -                pd[i] = pd_last[i];
> +            int end_offset = (s->x_offset + s->cur_w) * s->bpp;
> +            int end_len    = ls - end_offset;
> +            if (s->x_offset)
> +                memcpy(pd, pd_last, s->x_offset * s->bpp);
> +            if (end_len)
> +                memcpy(pd+end_offset, pd_last+end_offset, end_len);
>               pd      += s->image_linesize;
>               pd_last += s->image_linesize;
>           }
>       }
>   
>       for (j = s->y_offset + s->cur_h; j < s->height; j++) {
> -        for (i = 0; i < ls; i++)
> -            pd[i] = pd_last[i];
> +        memcpy(pd, pd_last, ls);
>           pd      += s->image_linesize;
>           pd_last += s->image_linesize;
>       }

Unless there is some more remarks on this one, I think it can be applied 
too.

Thanks,
-- 
Ben