Re: [FFmpeg-devel] [PATCH] postproc/postprocess_template: Fix left shift of negative numbers

From: Michael Niedermayer <michael@niedermayer.cc>
To: FFmpeg development discussions and patches <ffmpeg-devel@ffmpeg.org>
Subject: Re: [FFmpeg-devel] [PATCH] postproc/postprocess_template: Fix left shift of negative numbers
Date: Fri, 2 May 2025 01:45:00 +0200
Message-ID: <20250501234500.GW4991@pb2> (raw)
In-Reply-To: <AS8P250MB074474F049B1234C59694F2F8F832@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM>

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On Wed, Apr 30, 2025 at 08:36:01PM +0200, Andreas Rheinhardt wrote:
> Patch attached.
> 
> - Andreas

>  postprocess_template.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 805bee95b493f276f7802afbd7180c0f096ea52a  0001-postproc-postprocess_template-Fix-left-shift-of-nega.patch
> From 54ceac12363b666ad8005f282f6f9f08b6334b21 Mon Sep 17 00:00:00 2001
> From: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> Date: Wed, 30 Apr 2025 20:30:53 +0200
> Subject: [PATCH] postproc/postprocess_template: Fix left shift of negative
>  numbers
> 
> Affects the blocktest test tool.
> 
> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
> ---
>  libpostproc/postprocess_template.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libpostproc/postprocess_template.c b/libpostproc/postprocess_template.c
> index 0531e39477..fd8a4760af 100644
> --- a/libpostproc/postprocess_template.c
> +++ b/libpostproc/postprocess_template.c
> @@ -1060,8 +1060,8 @@ DERING_CORE((%0, %1, 8)       ,(%%FF_REGd, %1, 4),%%mm2,%%mm4,%%mm0,%%mm3,%%mm5,
>          if(src[stride*y + 8] > avg) t+= 256;
>          if(!rightborder && src[stride*y + 9] > avg) t+= 512;
>  
> -        t |= (~t)<<16;
> -        t &= (t<<1) & (t>>1);
> +        t |= (~t) * (1 << 16);
> +        t &= (t * 2) & (t>>1);
>          s[y] = t;

making t unsigned instead would keep the code more symmetric

thx

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Democracy is the form of government in which you can choose your dictator

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