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

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Date:	Wed, 23 May 2012 09:43:07 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
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, 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 9:31 AM, H. Peter Anvin <hpa@...or.com> wrote:
>>>
>>> And it should return UL for shift values < 32 and ULL otherwise.
>>
>
> Why do you want that behavior?  That seems bizarre...

We *have* to have that behavior.

A 64-bit value on a 32-bit architecture has fundamentally different
semantics than a 32-bit one.

It expands arithmetic, but it has other semantic differences too.
Think "printf()" etc. We don't want to force people to do 64-bit
arithmetic on x86-32 when they are working with BIT(0), for chrissake!

So if people make BIT(0) be a 64-bit value on a 32-bit architecture,
I'm going to run around naked with a chainsaw, and call people morons.
That's just not acceptable.

                  Linus
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