linux-kernel - WARNING:'hweight_long' include/linux/bitops.h compile warning problem.

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Date:	Mon, 20 Jun 2011 17:08:21 +0900
From:	NamJae Jeon <linkinjeon@...il.com>
To:	linux-kernel@...r.kernel.org, arnd@...db.de,
	linux-arch@...r.kernel.org
Subject: WARNING:'hweight_long' include/linux/bitops.h compile warning problem.

Hello. Arnd

I found compile warning while compiling module when using -Wsign-compare option.

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

I found the reason of this problem that the default return value of
the below macro is signed.

#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))) )

So, I try to add (unsigned long) in __const_hweight8 like this.

#define __const_hweight8(w)     (unsigned long )        \
     ( (!!((w) & (1ULL << 0))) +       \
       (!!((w) & (1ULL << 1))) +       \
       (!!((w) & (1ULL << 2))) +       \
       (!!((w) & (1ULL << 3))) +       \
       (!!((w) & (1ULL << 4))) +       \
       (!!((w) & (1ULL << 5))) +       \
       (!!((w) & (1ULL << 6))) +       \
       (!!((w) & (1ULL << 7))) )

so, I can't see compile warning after fixing it, Would you plz check this ?

Thanks.
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