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From: "Bjørn Mork" <bjorn@mork.no>
To: Dave Jones <davej@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Joe Perches <joe@perches.com>, Andy Whitcroft <apw@shadowen.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Jacob Pan <jacob.jun.pan@linux.intel.com>
Subject: Re: [PATCH] checkpatch: Warn on comparisons to true and false
Date: Thu, 11 Apr 2013 13:56:54 +0200	[thread overview]
Message-ID: <878v4pwa9l.fsf@nemi.mork.no> (raw)
In-Reply-To: <20130411021415.GA16118@redhat.com> (Dave Jones's message of "Wed, 10 Apr 2013 22:14:15 -0400")

Dave Jones <davej@redhat.com> writes:
> On Wed, Apr 10, 2013 at 03:57:51PM -0700, Andrew Morton wrote:
>  > On Tue, 09 Apr 2013 20:17:14 -0700 Joe Perches <joe@perches.com> wrote:
>  > 
>  > > Comparisons of A to true and false are better written
>  > > as A and !A.
>  > > 
>  > > Bleat a message on use.
>  > 
>  > hm.  I'm counting around 1,100 instances of "== true" and "== false".
>  > 
>  > That's a lot of people to shout at.  Is it really worthwhile? 
>  > "foo==true" is a bit of a waste of space but I can't say that I find it
>  > terribly offensive.
>
> It would be interesting to see how many people have historically screwed 
> up and used (!a) when they mean (a) and vice versa, versus spelling
> it out longform.  I'd be surprised if the results weren't skewed
> in favour of the more verbose form.

You have to consider that it is still possible to reverse the operator
even if spelling it out, so you don't really gain anything:

 bjorn@nemi:/usr/local/src/git/linux$ git grep -E '!=\s*(true|false)'|wc -l
 63

and since most of these compare to true, they are also at risk wrt
integers:

 bjorn@nemi:/usr/local/src/git/linux$ git grep -E '!=\s*true'|wc -l
 54

Based on a quick look at a few of these I guess they are mostly OK,
testing against bool values.  But I felt I had to share this little gem
which showed up in drivers/gpu/drm/exynos/exynos_drm_vidi.c:

static int vidi_power_on(struct vidi_context *ctx, bool enable)
{
        struct exynos_drm_subdrv *subdrv = &ctx->subdrv;
        struct device *dev = subdrv->dev;

        DRM_DEBUG_KMS("%s\n", __FILE__);

        if (enable != false && enable != true)
                return -EINVAL;
..


That's taking failsafe to the next step :)


Bjørn

  parent reply	other threads:[~2013-04-11 11:57 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-04-10  3:17 [PATCH] checkpatch: Warn on comparisons to true and false Joe Perches
2013-04-10  9:33 ` Andy Whitcroft
2013-04-10 11:27   ` Joe Perches
2013-04-10 12:41     ` Andy Whitcroft
2013-04-10 22:57 ` Andrew Morton
2013-04-11  1:07   ` Joe Perches
2013-04-11  2:14   ` Dave Jones
2013-04-11  3:47     ` Joe Perches
2013-04-11  8:19     ` Dan Carpenter
2013-04-11  8:29       ` Joe Perches
2013-04-11 11:56     ` Bjørn Mork [this message]
2013-04-11 14:25       ` Joe Perches

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