Commit c32fa99f authored Dec 18, 2013 by Paul Walmsley Committed by Ingo Molnar Feb 09, 2014

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@nvidia.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1312180459580.30198@tamien


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 49447903

include/asm-generic/bitops/const_hweight.h

+9 −8

Original line number	Diff line number	Diff line
		@@ -5,6 +5,7 @@
		* Compile time versions of __arch_hweightN()
		*/
		#define __const_hweight8(w) \
		((unsigned int) \
		((!!((w) & (1ULL << 0))) + \
		(!!((w) & (1ULL << 1))) + \
		(!!((w) & (1ULL << 2))) + \
		@@ -12,7 +13,7 @@
		(!!((w) & (1ULL << 4))) + \
		(!!((w) & (1ULL << 5))) + \
		(!!((w) & (1ULL << 6))) + \
		(!!((w) & (1ULL << 7))) )
		(!!((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))