linux-kernel - Re: [tip:x86/mce] x86/bitops: Move BIT

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Date:	Wed, 23 May 2012 18:53:03 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <borislav.petkov@....com>, mingo@...nel.org,
	linux-kernel@...r.kernel.org, frank.arnold@....com,
	akpm@...ux-foundation.org, torvalds@...ux-foundation.org,
	tglx@...utronix.de, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/mce] x86/bitops: Move BIT_64() for a wider use

On Wed, May 23, 2012 at 09:31:17AM -0700, H. Peter Anvin wrote:
> >>
> >> Actually we need a BIT() macro that works both
> >> on 32- and 64-bit. But that won't be that easy:
> >> http://lkml.indiana.edu/hypermail/linux/kernel/1010.1/02335.html
> >>
> >> And it should return UL for shift values < 32 and ULL otherwise.
> > 
> 
> Why do you want that behavior?  That seems bizarre...

I forgot to say "on 32-bit" above. So the sentence should've been:

"And it should return UL for shift values < 32 and ULL otherwise on
32-bit."

How about the following completely untested chunk:

#ifdef CONFIG_64BIT
#define BIT(nr)		(UC_64(1) << (nr))
#else
#define BIT(nr)	\
({ \
	unsigned _shift = (nr);	\
 	((_shift > 32) ? (U64_C(1) << _shift) : (U32_C(1) << _shift)); \
})
#endif

Ok? Too ugly? It still changes the return type of unsigned long to ULL
for shift values >= 32 and probably Linus doesn't want that...

Hmm.

-- 
Regards/Gruss,
    Boris.
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