Re: [PATCH] bitops: fix signedness of compile-time hweightimplementations

[Paul Walmsley]

Hi Peter, hpa, Arnd,

On Wed, 18 Dec 2013, Paul Walmsley wrote:

> 
> Enabling '-Wsign-compare' compiler warnings on code that includes
> include/linux/bitops.h can generate the following warning:
> 
> In file included from include/linux/kernel.h:10:0,
>                  from <random filename>:48:
> include/linux/bitops.h: In function ʽhweight_longʼ:
> include/linux/bitops.h:77:26: error: signed and unsigned type in conditional
> expression [-Werror=sign-compare]
> 
> (converted to an error with -Werror)
> 
> This is due to the use of the logical negation operator '!' in the
> __const_hweight8 macro in include/asm-generic/bitops/const_hweight.h.
> The use of that operator here results in a signed value.
> 
> Fix by explicitly casting the __const_hweight8 macro expansion to
> 'unsigned int'.  While here, clean up several checkpatch.pl warnings.
> 
> Signed-off-by: Paul Walmsley <pwalmsley@xxxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> Intended for v3.14.

Ping.  Just checking to see if you have any comments on this one, or if 
you're planning to send it upstream for v3.14.


- Paul

> 
>  include/asm-generic/bitops/const_hweight.h | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/asm-generic/bitops/const_hweight.h
> b/include/asm-generic/bitops/const_hweight.h
> index fa2a50b7ee66..40966203804d 100644
> --- a/include/asm-generic/bitops/const_hweight.h
> +++ b/include/asm-generic/bitops/const_hweight.h
> @@ -5,14 +5,15 @@
>   * Compile time versions of __arch_hweightN()
>   */
>  #define __const_hweight8(w)		\
> -      (	(!!((w) & (1ULL << 0))) +	\
> -	(!!((w) & (1ULL << 1))) +	\
> -	(!!((w) & (1ULL << 2))) +	\
> -	(!!((w) & (1ULL << 3))) +	\
> -	(!!((w) & (1ULL << 4))) +	\
> -	(!!((w) & (1ULL << 5))) +	\
> -	(!!((w) & (1ULL << 6))) +	\
> -	(!!((w) & (1ULL << 7)))	)
> +	((unsigned int)		\
> +	 ((!!((w) & (1ULL << 0))) +	\
> +	  (!!((w) & (1ULL << 1))) +	\
> +	  (!!((w) & (1ULL << 2))) +	\
> +	  (!!((w) & (1ULL << 3))) +	\
> +	  (!!((w) & (1ULL << 4))) +	\
> +	  (!!((w) & (1ULL << 5))) +	\
> +	  (!!((w) & (1ULL << 6))) +	\
> +	  (!!((w) & (1ULL << 7)))))
> 
>  #define __const_hweight16(w) (__const_hweight8(w)  + __const_hweight8((w)  >>
> 8 ))
>  #define __const_hweight32(w) (__const_hweight16(w) + __const_hweight16((w) >>
> 16))
> -- 
> 1.8.5.1
> 


- Paul