[FFmpeg-devel] [PATCH] avcodec/indeo3data: fix undefined left shift of negative number

[James Almer]

On 9/19/2015 1:53 AM, Ganesh Ajjanagadde wrote:
> This fixes a whole sea of -Wshift-negative-value reported with clang 3.7+, e.g
> http://fate.ffmpeg.org/log.cgi?time=20150918181527&log=compile&slot=x86_64-darwin-clang-polly-vectorize-stripmine-3.7.
> Any half decent compiler should anyway optimize away the multiplication.
> 
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/indeo3data.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/libavcodec/indeo3data.h b/libavcodec/indeo3data.h
> index e7e28a3..7a2df12 100644
> --- a/libavcodec/indeo3data.h
> +++ b/libavcodec/indeo3data.h
> @@ -237,10 +237,11 @@
>   * Pack two delta values (a,b) into one 16bit word
>   * according with endianness of the host machine.
>   */
> +#define POW_2(n) (1 << (n))
>  #if HAVE_BIGENDIAN
> -#define PD(a,b) (((a) << 8) + (b))
> +#define PD(a,b) (((a) * POW_2(8)) + (b))

#define PD(a,b) (((a) * (1 << 8)) + (b))

Is more in line with previous similar changes. See for example commits 4eee685a,
e50ae60d and many others.

Same for the lines below.

>  #else
> -#define PD(a,b) (((b) << 8) + (a))
> +#define PD(a,b) (((b) * POW_2(8)) + (a))
>  #endif
>  
>  /**
> @@ -285,9 +286,9 @@ static const int16_t delta_tab_3_5[79]  = { TAB_3_5 };
>   * according with endianness of the host machine.
>   */
>  #if HAVE_BIGENDIAN
> -#define PD(a,b) (((a) << 24) + ((a) << 16) + ((b) << 8) + (b))
> +#define PD(a,b) (((a) * POW_2(24)) + ((a) * POW_2(16)) + ((b) * POW_2(8)) + (b))
>  #else
> -#define PD(a,b) (((b) << 24) + ((b) << 16) + ((a) << 8) + (a))
> +#define PD(a,b) (((b) * POW_2(24)) + ((b) * POW_2(16)) + ((a) * POW_2(8)) + (a))
>  #endif
>  
>  /*
>