linux-kernel - Re: [RFC] lib: crc8: add new library module providing crc8 algorithm

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Message-ID: <4DDBE432.3040207@broadcom.com>
Date:	Tue, 24 May 2011 19:00:34 +0200
From:	"Arend van Spriel" <arend@...adcom.com>
To:	"Alan Cox" <alan@...rguk.ukuu.org.uk>
cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	"Dan Carpenter" <error27@...il.com>
Subject: Re: [RFC] lib: crc8: add new library module providing crc8
 algorithm

On 05/24/2011 02:57 PM, Alan Cox wrote:
> On Tue, 24 May 2011 12:38:45 +0200
> "Arend van Spriel"<arend@...adcom.com>  wrote:
>
>> On 05/24/2011 12:27 PM, Alan Cox wrote:
>>>> Not sure whether you mean the source code or the object code. I build
>>>> kernel with debug symbols so the sizes are bit higher.
>>> nm will tell you the actual sizes. I think the n_gsm code is about 500
>>> bytes or so and chunks of it inline.
>> Not counting the crc table I assume.
> I forget but I think including - its a tiny tiny bit of code once inlined.

I used nm on both flavours.

dynamic crc table based on polynomial and bit order
---------------------------------------------------
00000000 00000026 T crc8
00000030 000000dc T crc8_create

fixed crc table with table selection based on bit order
-------------------------------------------------------
00000000 00000026 T crc8
00000030 0000002b T crc8_create
00000100 00000100 r crc8_table_lsb
00000000 00000100 r crc8_table_msb

The first requires the user to provide buffer to hold the table. The 
difference is in the crc_create() function (maybe better named 
crc_populate_table() in first, and crc_select_table() in second). It is 
177 bytes larger. The crc calculating function is 38 bytes. Still pretty 
small I would think.

Gr. AvS

-- 
Almost nobody dances sober, unless they happen to be insane.
-- H.P. Lovecraft --


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