[PATCH] bitops: fix signedness of compile-time hweight implementations

[PATCH] bitops: fix signedness of compile-time hweight implementations

[Paul Walmsley]

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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 ‘hweight_long’:
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@nvidia.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnd Bergmann <arnd@arndb.de>
---
Intended for v3.14.

  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

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

[Paul Walmsley]

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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 ‘hweight_long’:
> 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@nvidia.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Cc: Arnd Bergmann <arnd@arndb.de>
> ---
> 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

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

[Peter Zijlstra]

On Wed, Jan 22, 2014 at 05:19:58PM +0000, Paul Walmsley wrote:
> 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 ‘hweight_long’:
> > 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@nvidia.com>
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > Cc: Arnd Bergmann <arnd@arndb.de>
> > ---
> > 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.

I'm not sure through which tree to send it, but just I've queued it so
it doesn't get lost again.

Also, it didn't apply as is for some reason, hit it on the head with a
hammer though.