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Date: Sat, 23 Dec 2000 09:15:13 -0800 (PST)
From: <keyser-lk@soze.net>
To: Sourav Sen <sourav@csa.iisc.ernet.in>
Cc: <linux-kernel@vger.kernel.org>
Subject: Re: whats happening
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On Sat, 23 Dec 2000, Sourav Sen wrote:

> In some parts of the kernel code I find expression like
>
> len = (len + ~PAGE_MASK) & PAGE_MASK ;
>
> Whats happening to len?

It's being aligned properly.

if you have a continuous array of objects that are each 8 bytes, you
create a mask that's FFFFFFF8, then if len=7, instead of doing an
operation on the last byte of the first thing and the first 7 bytes of the
second, the above expression will add 7, making len 14, then normalize it
to the last valid object address, 8.  And if you start with a valid
address, you get that same address back.


justin
-- 
To summon a demon you must first know its name.


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