linux-kernel - Re: [ 57/72] genirq: Unmask oneshot irqs when thread was not woken

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Message-ID: <CA+55aFzqF0C1eiidR=ycJ0DhV3MiWJRkOmi-GEcgT7J6Dm+a5g@mail.gmail.com>
Date:	Tue, 6 Mar 2012 13:47:09 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Sven Joachim <svenjoac@....de>,
	Stefan Lippers-Hollmann <s.L-H@....de>,
	Greg KH <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>, stable@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Jonathan Nieder <jrnieder@...il.com>,
	linux-wireless@...r.kernel.org,
	Stefano Brivio <stefano.brivio@...imi.it>
Subject: Re: [ 57/72] genirq: Unmask oneshot irqs when thread was not woken

On Tue, Mar 6, 2012 at 1:40 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> (*) "1 << ffz(a)" can be written as
>
>   a = ~a;        /* Turn the zero bits into 1 bits */
>   a &= -a;      /* .. and find the first one. */
>
> without ever doing any insane bit scanning.

Alternatively, wite it directly as "(a+1) &~a", which is the same
expression just written differently (due to "-a == ~a+1")

Yeah, I've been playing too much with the bitwise optimizations of the
dentry cache name comparisons lately.

                   Linus
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