[FFmpeg-devel] [PATCHv2] all: do standards compliant absdiff computation

[Ganesh Ajjanagadde]

On Wed, Sep 16, 2015 at 2:48 PM, Ganesh Ajjanagadde
<gajjanagadde at gmail.com> wrote:
> This resolves implementation defined behavior, and also silences -Wabsolute-value in clang 3.5+.
> Moreover, the generated asm is identical to before modulo nop padding.
>
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/flashsv2enc.c | 8 +++++---
>  libavfilter/vf_hqx.c     | 8 +++++---
>  libavfilter/vf_xbr.c     | 7 ++++---
>  3 files changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/libavcodec/flashsv2enc.c b/libavcodec/flashsv2enc.c
> index c2c00f4..65db112 100644
> --- a/libavcodec/flashsv2enc.c
> +++ b/libavcodec/flashsv2enc.c
> @@ -412,12 +412,14 @@ static inline unsigned pixel_color15(const uint8_t * src)
>
>  static inline unsigned int chroma_diff(unsigned int c1, unsigned int c2)
>  {
> +#define ABSDIFF(a,b) (abs((int)(a)-(int)(b)))
> +
>      unsigned int t1 = (c1 & 0x000000ff) + ((c1 & 0x0000ff00) >> 8) + ((c1 & 0x00ff0000) >> 16);
>      unsigned int t2 = (c2 & 0x000000ff) + ((c2 & 0x0000ff00) >> 8) + ((c2 & 0x00ff0000) >> 16);
>
> -    return abs(t1 - t2) + abs((c1 & 0x000000ff) - (c2 & 0x000000ff)) +
> -        abs(((c1 & 0x0000ff00) >> 8) - ((c2 & 0x0000ff00) >> 8)) +
> -        abs(((c1 & 0x00ff0000) >> 16) - ((c2 & 0x00ff0000) >> 16));
> +    return ABSDIFF(t1, t2) + ABSDIFF(c1 & 0x000000ff, c2 & 0x000000ff) +
> +        ABSDIFF((c1 & 0x0000ff00) >> 8 , (c2 & 0x0000ff00) >> 8) +
> +        ABSDIFF((c1 & 0x00ff0000) >> 16, (c2 & 0x00ff0000) >> 16);
>  }
>
>  static inline int pixel_color7_fast(Palette * palette, unsigned c15)
> diff --git a/libavfilter/vf_hqx.c b/libavfilter/vf_hqx.c
> index fa15d9c..d1e360f 100644
> --- a/libavfilter/vf_hqx.c
> +++ b/libavfilter/vf_hqx.c
> @@ -65,9 +65,11 @@ static av_always_inline int yuv_diff(uint32_t yuv1, uint32_t yuv2)
>  #define YMASK 0xff0000
>  #define UMASK 0x00ff00
>  #define VMASK 0x0000ff
> -    return abs((yuv1 & YMASK) - (yuv2 & YMASK)) > (48 << 16) ||
> -           abs((yuv1 & UMASK) - (yuv2 & UMASK)) > ( 7 <<  8) ||
> -           abs((yuv1 & VMASK) - (yuv2 & VMASK)) > ( 6 <<  0);
> +#define ABSDIFF(a,b) (abs((int)(a)-(int)(b)))
> +
> +    return ABSDIFF(yuv1 & YMASK, yuv2 & YMASK) > (48 << 16) ||
> +           ABSDIFF(yuv1 & UMASK, yuv2 & UMASK) > ( 7 <<  8) ||
> +           ABSDIFF(yuv1 & VMASK, yuv2 & VMASK) > ( 6 <<  0);
>  }
>
>  /* (c1*w1 + c2*w2) >> s */
> diff --git a/libavfilter/vf_xbr.c b/libavfilter/vf_xbr.c
> index 8586608..c92e9a8 100644
> --- a/libavfilter/vf_xbr.c
> +++ b/libavfilter/vf_xbr.c
> @@ -65,13 +65,14 @@ static uint32_t pixel_diff(uint32_t x, uint32_t y, const uint32_t *r2y)
>  #define YMASK 0xff0000
>  #define UMASK 0x00ff00
>  #define VMASK 0x0000ff
> +#define ABSDIFF(a,b) (abs((int)(a)-(int)(b)))
>
>      uint32_t yuv1 = r2y[x & 0xffffff];
>      uint32_t yuv2 = r2y[y & 0xffffff];
>
> -    return (abs((yuv1 & YMASK) - (yuv2 & YMASK)) >> 16) +
> -           (abs((yuv1 & UMASK) - (yuv2 & UMASK)) >>  8) +
> -           abs((yuv1 & VMASK) - (yuv2 & VMASK));
> +    return (ABSDIFF(yuv1 & YMASK, yuv2 & YMASK) >> 16) +
> +           (ABSDIFF(yuv1 & UMASK, yuv2 & UMASK) >>  8) +
> +            ABSDIFF(yuv1 & VMASK, yuv2 & VMASK);
>  }
>
>  #define ALPHA_BLEND_128_W(a, b) ((((a) & LB_MASK) >> 1) + (((b) & LB_MASK) >> 1))
> --
> 2.5.2
>

ping; the macro has now been localized.