Re: [PATCH] bitops: fix signedness of compile-time hweight implementations
From: Paul Walmsley <hidden>
Date: 2014-01-22 17:20:01
Also in:
lkml
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 <redacted>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <redacted>
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
quoted hunk ↗ jump to hunk
include/asm-generic/bitops/const_hweight.h | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-)diff --git a/include/asm-generic/bitops/const_hweight.hb/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