[FFmpeg-devel] [PATCH 2/2] swscale/unscaled: remove redundant subtraction

[Niklas Haas]

On Tue, 17 Dec 2024 15:27:41 +0100 Niklas Haas <ffmpeg at haasn.xyz> wrote:
> From: Niklas Haas <git at haasn.dev>
>
> tmp is already right-shifted to dst_depth, so tmp >> dst_depth is always 0.

This is not true in the case of overflow. Dropping this commit.

>
> Signed-off-by: Niklas Haas <git at haasn.dev>
> Sponsored-by: Sovereign Tech Fund
> ---
>  libswscale/swscale_unscaled.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/libswscale/swscale_unscaled.c b/libswscale/swscale_unscaled.c
> index ea6fb038bc..97a51097f2 100644
> --- a/libswscale/swscale_unscaled.c
> +++ b/libswscale/swscale_unscaled.c
> @@ -2098,17 +2098,17 @@ static int packedCopyWrapper(SwsInternal *c, const uint8_t *const src[],
>          for (i = 0; i < height; i++) {\
>              const uint8_t *dither= dithers[shift-1][i&7];\
>              for (j = 0; j < length-7; j+=8) {\
> -                tmp = (bswap(src[j+0]) + dither[0])>>shift; dst[j+0] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+1]) + dither[1])>>shift; dst[j+1] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+2]) + dither[2])>>shift; dst[j+2] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+3]) + dither[3])>>shift; dst[j+3] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+4]) + dither[4])>>shift; dst[j+4] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+5]) + dither[5])>>shift; dst[j+5] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+6]) + dither[6])>>shift; dst[j+6] = dbswap(tmp - (tmp>>dst_depth));\
> -                tmp = (bswap(src[j+7]) + dither[7])>>shift; dst[j+7] = dbswap(tmp - (tmp>>dst_depth));\
> +                dst[j+0] = dbswap((bswap(src[j+0]) + dither[0])>>shift);\
> +                dst[j+1] = dbswap((bswap(src[j+1]) + dither[1])>>shift);\
> +                dst[j+2] = dbswap((bswap(src[j+2]) + dither[2])>>shift);\
> +                dst[j+3] = dbswap((bswap(src[j+3]) + dither[3])>>shift);\
> +                dst[j+4] = dbswap((bswap(src[j+4]) + dither[4])>>shift);\
> +                dst[j+5] = dbswap((bswap(src[j+5]) + dither[5])>>shift);\
> +                dst[j+6] = dbswap((bswap(src[j+6]) + dither[6])>>shift);\
> +                dst[j+7] = dbswap((bswap(src[j+7]) + dither[7])>>shift);\
>              }\
>              for (; j < length; j++) {\
> -                tmp = (bswap(src[j]) + dither[j&7])>>shift; dst[j] = dbswap(tmp - (tmp>>dst_depth));\
> +                dst[j] = dbswap((bswap(src[j]) + dither[j&7])>>shift);\
>              }\
>              dst += dstStride;\
>              src += srcStride;\
> --
> 2.47.0
>
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