linux-kernel - Re: [PATCH] include: Fix compile warning in include/linux/bitops.h

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Date:	Tue, 12 Jun 2012 09:05:40 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	arnd@...db.de, linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] include: Fix compile warning in include/linux/bitops.h

2012/6/12, Andrew Morton <akpm@...ux-foundation.org>:
> On Fri,  8 Jun 2012 23:15:30 -0400
> Namjae Jeon <linkinjeon@...il.com> wrote:
>
>> The compile warning is caused by __const_hweight8 when using
>> hweight_long with -Wsign-compare option.
>> The reason is that the default return value of this macro is signed.
>> So need type casting to remove warning.
>
> um, what warning?
Hi Andrew.
Sorry, I forgot it.
When we use hwight_long function, We can see the below warning message.

include/linux/bitops.h: In function 'hweight_long':
include/linux/bitops.h:49: warning: signed and unsigned type in
conditional expression

Thanks a lot.
>
> Please always quote the compiler messages when fixing build warnings or
> errors.
>
>> index fa2a50b..3ad0dae 100644
>> --- a/include/asm-generic/bitops/const_hweight.h
>> +++ b/include/asm-generic/bitops/const_hweight.h
>> @@ -4,7 +4,7 @@
>>  /*
>>   * Compile time versions of __arch_hweightN()
>>   */
>> -#define __const_hweight8(w)		\
>> +#define __const_hweight8(w)	(unsigned long)	\
>>        (	(!!((w) & (1ULL << 0))) +	\
>>  	(!!((w) & (1ULL << 1))) +	\
>>  	(!!((w) & (1ULL << 2))) +	\
>
>
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