linux-kernel - Re: [GIT pull] core/urgent for v5.4-rc7

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Date:   Mon, 11 Nov 2019 17:37:26 -0800
From:   Joe Perches <joe@...ches.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>, Jiri Slaby <jslaby@...e.cz>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [GIT pull] core/urgent for v5.4-rc7

On Mon, 2019-11-11 at 09:12 -0800, Linus Torvalds wrote:
> On Sun, Nov 10, 2019 at 5:50 PM Joe Perches <joe@...ches.com> wrote:
> > The !! logical usage is not particularly common in the kernel.
> > There seems to be only a couple/few dozen.
> 
> Your grep pattern is for the explicitly silly "turn a boolean to a
> boolean". That should certainly be rare.
> 
> But I meant it in a more general way - there's a lot of common use of
> "!!" for "turn this expression into a boolean". A trivial grep for
> that (didn't check how correct it was - there might be comments that
> are very excited too) implies that we have a fair amount of this
> pattern:
> 
>     $ git grep '[^!]!![^!]' -- '*.[ch]' | wc -l
>     7007

Likely the majority of those are bit comparison coercions to 0/1 like

	int val = !!(A & B)

> so the '!!' pattern itself isn't rare.

And likely these !! patterns are preferred to (A & B) != 0

I don't care much either way as either form, unlike !!(A == B),
is not redundant.