[FFmpeg-devel] [PATCH 5/5] avcodec/utvideodec: Factor multiply out of inner loop

[Steven Liu]

2017-06-28 3:47 GMT+08:00 Michael Niedermayer <michael at niedermayer.cc>:
> 0.5% faster loop
>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libavcodec/utvideodec.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/libavcodec/utvideodec.c b/libavcodec/utvideodec.c
> index 788f4475b9..a20e28320c 100644
> --- a/libavcodec/utvideodec.c
> +++ b/libavcodec/utvideodec.c
> @@ -196,7 +196,8 @@ static int decode_plane10(UtvideoContext *c, int plane_no,
>
>          prev = 0x200;
>          for (j = sstart; j < send; j++) {
> -            for (i = 0; i < width * step; i += step) {
> +            int ws = width * step;
> +            for (i = 0; i < ws; i += step) {
>                  pix = get_vlc2(&gb, vlc.table, VLC_BITS, 3);
>                  if (pix < 0) {
>                      av_log(c->avctx, AV_LOG_ERROR, "Decoding error\n");
> @@ -300,7 +301,8 @@ static int decode_plane(UtvideoContext *c, int plane_no,
>
>          prev = 0x80;
>          for (j = sstart; j < send; j++) {
> -            for (i = 0; i < width * step; i += step) {
> +            int ws = width * step;
> +            for (i = 0; i < ws; i += step) {
>                  pix = get_vlc2(&gb, vlc.table, VLC_BITS, 3);
>                  if (pix < 0) {
>                      av_log(c->avctx, AV_LOG_ERROR, "Decoding error\n");
> --
> 2.13.0
>
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LGTM, move the compute before the loop, better then in the loop