linux-kernel - Re: [PATCH] checkpatch: Add --strict preference for #defines using BIT(foo)

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Message-Id: <20141110153647.f98f7d60fa24bf3bf7cbc215@linux-foundation.org>
Date:	Mon, 10 Nov 2014 15:36:47 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>, jiri@...nulli.us,
	netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] checkpatch: Add --strict preference for #defines using
 BIT(foo)

On Fri, 07 Nov 2014 13:15:39 -0800 Joe Perches <joe@...ches.com> wrote:

> Using BIT(foo) and BIT_ULL(bar) is more common now.
> Suggest using these macros over #defines with 1<<value.

urgh.  I'm counting eightish implementations of BIT(), an unknown
number of which are actually being used.  Many use 1<<n, some use
1UL<<N, another uses 1ULL<<n.  I'm a bit reluctant to recommend that
anyone should use BIT() until it has has some vigorous scrubbing :(

Is it actually an improvement?  If I see

#define X	(1U << 7)

then I know exactly what it does.  Whereas when I see

#define X	BIT(7)

I know neither the size or the signedness of X so I have to go look it
up.

I have no strong feelings either way, but I'm wondering what might have
inspired this change?

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