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To: "Perez-Gonzalez, Inaky" <inaky.perez-gonzalez@intel.com>
Cc: alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] include/asm-ARCH/page.h:get_order() Reorganize and op timize
References: <A46BBDB345A7D5118EC90002A5072C7806CAC93A@orsmsx116.jf.intel.com>
From: Falk Hueffner <falk.hueffner@student.uni-tuebingen.de>
Date: 14 Nov 2002 01:26:08 +0100
In-Reply-To: <A46BBDB345A7D5118EC90002A5072C7806CAC93A@orsmsx116.jf.intel.com>
Message-ID: <87u1ilov33.fsf@student.uni-tuebingen.de>
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"Perez-Gonzalez, Inaky" <inaky.perez-gonzalez@intel.com> writes:

> > >     s = --s >> PAGE_SHIFT;
> > 
> > This code has undefined behaviour.
>  
> Do you mean that this:
> 
> s = (s-1) >> PAGE_SHIFT
> 
> is more deterministic? If so, I agree -- if you mean something else,
> I am kind of lost.

I mean that this code violates the rule that you may modify a value
only once between two sequence points. Newer gccs have a warning for
this (-Wsequence-point), the info page tells more.

Also, did I understand it right that you want to use fls even on
architectures that don't have it as a builtin? I would guess that will
actually be noticeably slower, since generic_fls is so complicated.

-- 
	Falk
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