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

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Date:	Wed, 18 Dec 2013 05:02:14 -0800
From:	Paul Walmsley <pwalmsley@...dia.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] bitops: fix signedness of compile-time hweight
 implementations


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@...dia.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Arnd Bergmann <arnd@...db.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