[FFmpeg-devel] [PATCH 1/3] swscale/input: Fix several invalid shifts related to rgb2yuv constants

[Andreas Rheinhardt]

On Tue, Jan 21, 2020 at 11:18 PM Michael Niedermayer <michael at niedermayer.cc>
wrote:

> Fixes: Invalid shifts
> Fixes: #8140
> Fixes: #8146
>
> Signed-off-by: Michael Niedermayer <michael at niedermayer.cc>
> ---
>  libswscale/input.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/libswscale/input.c b/libswscale/input.c
> index 064f8da314..159f70307d 100644
> --- a/libswscale/input.c
> +++ b/libswscale/input.c
> @@ -286,8 +286,8 @@ static av_always_inline void
> rgb16_32ToUV_c_template(int16_t *dstU,
>                                                       int gsh, int bsh,
> int S,
>                                                       int32_t *rgb2yuv)
>  {
> -    const int ru       = rgb2yuv[RU_IDX] << rsh, gu = rgb2yuv[GU_IDX] <<
> gsh, bu = rgb2yuv[BU_IDX] << bsh,
> -              rv       = rgb2yuv[RV_IDX] << rsh, gv = rgb2yuv[GV_IDX] <<
> gsh, bv = rgb2yuv[BV_IDX] << bsh;
> +    const int ru       = rgb2yuv[RU_IDX] * (1 << rsh), gu =
> rgb2yuv[GU_IDX] * (1 << gsh), bu = rgb2yuv[BU_IDX] * (1 << bsh),
> +              rv       = rgb2yuv[RV_IDX] * (1 << rsh), gv =
> rgb2yuv[GV_IDX] * (1 << gsh), bv = rgb2yuv[BV_IDX] * (1 << bsh);
>      const unsigned rnd = (256u<<((S)-1)) + (1<<(S-7));
>      int i;
>
> @@ -314,8 +314,8 @@ static av_always_inline void
> rgb16_32ToUV_half_c_template(int16_t *dstU,
>                                                            int gsh, int
> bsh, int S,
>                                                            int32_t
> *rgb2yuv)
>  {
> -    const int ru       = rgb2yuv[RU_IDX] << rsh, gu = rgb2yuv[GU_IDX] <<
> gsh, bu = rgb2yuv[BU_IDX] << bsh,
> -              rv       = rgb2yuv[RV_IDX] << rsh, gv = rgb2yuv[GV_IDX] <<
> gsh, bv = rgb2yuv[BV_IDX] << bsh,
> +    const int ru       = rgb2yuv[RU_IDX] * (1 << rsh), gu =
> rgb2yuv[GU_IDX] * (1 << gsh), bu = rgb2yuv[BU_IDX] * (1 << bsh),
> +              rv       = rgb2yuv[RV_IDX] * (1 << rsh), gv =
> rgb2yuv[GV_IDX] * (1 << gsh), bv = rgb2yuv[BV_IDX] * (1 << bsh),
>                maskgx   = ~(maskr | maskb);
>      const unsigned rnd = (256U<<(S)) + (1<<(S-6));
>      int i;
> --

When I looked into this last year, I was unable to ascertain that the
multiplication wouldn't overflow (in which case one would need to go the
unsigned route, most easily by making the rgb2yuv parameter a uint32_t *).
Can you?

This also fixes lots of FATE-tests, 37 if I am not mistaken:
filter-overlay_yuv420_yuva420, filter-overlay_yuv422_yuva422,
ffmpeg-filter_colorkey, sub2video, vsynth1-ffv1-v3-bgr0,
vsynth3-huffyuvbgr24, vsynth_lena-mov-bpp15, ...

- Andreas