Re: [FFmpeg-devel] [PATCH 1/5] avcodec/ppc/hpeldsp_altivec: Fix left-shift of negative number

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Andreas Rheinhardt:
> It is UB and affected e.g. the vp5 and vp61 FATE tests:
> https://fate.ffmpeg.org/report.cgi?time=20240327083327&slot=ppc-linux-gcc-13.2-ubsan-altivec-qemu
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libavcodec/ppc/hpeldsp_altivec.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavcodec/ppc/hpeldsp_altivec.c b/libavcodec/ppc/hpeldsp_altivec.c
> index a531b6b6ec..4bf6b28ed6 100644
> --- a/libavcodec/ppc/hpeldsp_altivec.c
> +++ b/libavcodec/ppc/hpeldsp_altivec.c
> @@ -41,9 +41,9 @@ void ff_put_pixels16_altivec(uint8_t *block, const uint8_t *pixels, ptrdiff_t li
>      register vector unsigned char pixelsv1D;
>  
>      int i;
> -    register ptrdiff_t line_size_2 = line_size << 1;
> +    register ptrdiff_t line_size_2 = line_size * (1 << 1);
>      register ptrdiff_t line_size_3 = line_size + line_size_2;
> -    register ptrdiff_t line_size_4 = line_size << 2;
> +    register ptrdiff_t line_size_4 = line_size * (1 << 2);
>  
>  // hand-unrolling the loop by 4 gains about 15%
>  // mininum execution time goes from 74 to 60 cycles

Will apply the remainder of this patchset tomorrow unless there are
objections.

- Andreas

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