[FFmpeg-devel] [PATCH 2/2] lavfi/lut: simplify nested lut plane stepping.

[Wang Bin]

2013/4/17 Clément Bœsch <ubitux at gmail.com>

> ---
>  libavfilter/vf_lut.c | 14 +++++---------
>  1 file changed, 5 insertions(+), 9 deletions(-)
>
> diff --git a/libavfilter/vf_lut.c b/libavfilter/vf_lut.c
> index be497ac..21309a5 100644
> --- a/libavfilter/vf_lut.c
> +++ b/libavfilter/vf_lut.c
> @@ -286,15 +286,11 @@ static int filter_frame(AVFilterLink *inlink,
> AVFrame *in)
>              inrow  = inrow0;
>              outrow = outrow0;
>              for (j = 0; j < w; j++) {
> -                outrow[0] = tab[0][inrow[0]];
> -                if (lut->step>1) {
> -                    outrow[1] = tab[1][inrow[1]];
> -                    if (lut->step>2) {
> -                        outrow[2] = tab[2][inrow[2]];
> -                        if (lut->step>3) {
> -                            outrow[3] = tab[3][inrow[3]];
> -                        }
> -                    }
> +                switch (lut->step) {
> +                case 3:  outrow[3] = tab[3][inrow[3]]; // Fall-through
> +                case 2:  outrow[2] = tab[2][inrow[2]]; // Fall-through
> +                case 1:  outrow[1] = tab[1][inrow[1]]; // Fall-through
> +                default: outrow[0] = tab[0][inrow[0]];
>                  }
>                  outrow += lut->step;
>                  inrow  += lut->step;
>
>
I think this patch does not equals to the original code. For example, if
lut->step == 3, the original code will run
outrow[0] = tab[0][inrow[0]];
outrow[1] = tab[1][inrow[1]];
outrow[2] = tab[2][inrow[2]];
but the patch code will only run
outrow[3] = tab[3][inrow[3]];
outrow[0] = tab[0][inrow[0]];
I don't know which code is right, but i'm sure the result is different.