[FFmpeg-devel] [PATCH]lavfi/fspp: Add a cast to silence a clang warning

[James Almer]

On 4/13/2019 7:04 PM, Carl Eugen Hoyos wrote:
> Hi!
> 
> Attached patch silences two warnings shown when compiling with clang:
> libavfilter/vf_fspp.h:51:42: warning: implicit conversion from 'int'
> to 'int16_t' (aka 'short') changes value from 44130 to -21406
> 
> Please comment, Carl Eugen
> 
> 
> 0001-lavfi-vf_fspp-Use-the-intended-cast-to-int16_t.patch
> 
> From d731e523d9c5854183d20d37fe921f49fb048498 Mon Sep 17 00:00:00 2001
> From: Carl Eugen Hoyos <ceffmpeg at gmail.com>
> Date: Sat, 13 Apr 2019 23:05:44 +0200
> Subject: [PATCH] lavfi/fspp: Add two casts to int16_t.
> 
> Silences a warning with clang:
> warning: implicit conversion from 'int' to 'int16_t' (aka 'short') changes value from 44130 to -21406
> ---
>  libavfilter/vf_fspp.h |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/libavfilter/vf_fspp.h b/libavfilter/vf_fspp.h
> index 74a3447..e346439 100644
> --- a/libavfilter/vf_fspp.h
> +++ b/libavfilter/vf_fspp.h
> @@ -31,7 +31,7 @@
>  #define DCTSIZE 8
>  #define DCTSIZE_S "8"
>  
> -#define FIX(x,s)  ((int) ((x) * (1 << s) + 0.5) & 0xffff)
> +#define FIX(x,s)  ((int16_t)((x) * (1 << s) + 0.5) & (int16_t)0xffff)

The "& 0xffff" is turning -21406 into 44130 since it zeroes all the high
bits, and then that value gets converted back to -21406 when stored into
an int16_t variable.

Change the int cast into int16_t if you want since it doesn't hurt (all
the values are safely within the int16_t range anyway), but remove the
"& 0xffff" altogether instead of casting it, to get rid of this warning.

>  #define C64(x)    ((uint64_t)((x) | (x) << 16)) <<32 | (uint64_t)(x) | (uint64_t)(x) << 16
>  #define FIX64(x,s)  C64(FIX(x,s))
>  
> -- 1.7.10.4
> 
> 
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