linux-kernel - Re: There are smaller ways to encode a CRC32 table...

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Message-Id: <1201862252.25409.69.camel@localhost.localdomain>
Date:	Fri, 01 Feb 2008 10:37:32 +0000
From:	Ian Campbell <ijc@...lion.org.uk>
To:	George Spelvin <linux@...izon.com>
Cc:	hpa@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
	mingo@...hat.com
Subject: Re: There are smaller ways to encode a CRC32 table...


On Thu, 2008-01-31 at 23:53 -0500, George Spelvin wrote:
> The code to fill it in is smaller than the table itself.
> Is it worth complicating things with some INIT code to reduce
> the stored image size?  (The table is not compressible.)
[snip]

Thanks but since the code is only used when building the image I'm not
too worried which way is used and I've tested the table based one ;-).

> And BTW, storing the inverse of the CRC only catches trailing (after the CRC)
> all-zero padding.  If this is not a problem, it's not necessary, although you
> still might want to do it just for consistency.  This inversion changes the
> CRC of the entire image (body + CRC) from all-zero to a fixed non-zero value.
> (To be precise, to the (non-inverted) CRC of 0xffffffff.)

I didn't know the precise details of why you might invert it, thanks for
the info.

Ian
-- 
Ian Campbell
Current Noise: Reverend Bizarre - Sodoma Sunrise

I am a man: nothing human is alien to me.
		-- Publius Terentius Afer (Terence)

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