linux-kernel - Re: [PATCH 03/10] AXFS: axfs.h

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Date:	Fri, 22 Aug 2008 11:12:32 -0700
From:	"Jared Hulbert" <jaredeh@...il.com>
To:	"Geert Uytterhoeven" <Geert.Uytterhoeven@...ycom.com>
Cc:	"Arnd Bergmann" <arnd@...db.de>, Linux-kernel@...r.kernel.org,
	linux-embedded@...r.kernel.org,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	"Jörn Engel" <joern@...fs.org>,
	tim.bird@...sony.com, cotte@...ibm.com, nickpiggin@...oo.com.au
Subject: Re: [PATCH 03/10] AXFS: axfs.h

>> So do I understand right that 3 bytes is your minimum size, and going
>> smaller than that would not be helpful? Otherwise I would assume that
>> storing a '5' should only take one byte instead of three.

Right.  But you need 3 bytes to store the maximum value 0x0a0000

If we had:
0x0000000000000003
0x00000000000000FF
0x000000000000000A

You would only need a 1 byte depth.

> From the paper, the minimum size (called `depth') is 1.

Correct the depth can be from 1 to 8 bytes.  The depth is determined
by the maximum value in the array.

>> I don't unsterstand yet why you store the length of each word separate
>> from the word. Most variable-length codes store that implicitly in
>> the data itself, e.g. in the upper three bits, so that for storing
>> 0x5, 0x1001, 0xa0000, this could e.g. end up as 0x054010014a0000,
>> which is shorter than what you have, but not harder to decode.
>
> AFAIU, the length (`depth') of each word is not stored separate, as the
> depth is the same for all values in the same table.

That is correct.  Each table has a single depth stored in the region descriptor.
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