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

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Date:	Wed, 25 May 2011 07:21:37 +0200
From:	"Arend van Spriel" <arend@...adcom.com>
To:	"George Spelvin" <linux@...izon.com>
cc:	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"error27@...il.com" <error27@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"linville@...driver.com" <linville@...driver.com>
Subject: Re: [RFC] lib: crc8: add new library module providing crc8
 algorithm

On 05/25/2011 12:52 AM, George Spelvin wrote:
>> V3:
>> - added function crc8_create().
>> - crc8_create() takes polynomial and bit direction as parameters.
> May I suggest that crc8_create is A Stupid Idea.  Since the bit order
> (and polynomial) will always be compile-time constants, just let the
> call sites call crc8_create_[lm]sb_first() directly.

Thanks for be subtle in your suggestion. The crc8 module can have 
multiple callers, which have their own bit order and polynomial. From 
caller perspective they are likely compile-time constants. You are right 
that the extra layer crc8_create is not adding much and callers should 
the bit order specific create functions directly.
> That way there's no need for the enum, and specifying something
> other than lsb_first and msb_first is a compile-time error rather than
> a run-time one

If callers use the specific function they can not specify a bit order so 
no compile-time error.

> It might be nice to add some const declarations, and use size_t
> for the buffer length:
> u8 crc8(u8 const *table, u8 const *pdata, size_t nbytes, u8 crc)
> or
> u8 crc8(u8 const table[256], u8 const *pdata, size_t nbytes, u8 crc)
>
>
> Style points you might consider, but I do not consider essential:
>
> Personally, when a function parameter is a pointer to
> a fixed-size array, I prefer to declare it as
> 	void crc8_create_lsb_first(u8 table[256], u8 poly)
> for better documentation, but that's your choice.
>
> The CRC8_GOOD_VALUE could be explained if you like.  "If a CRC is inverted
> before transmission, the CRC computed over the while (message+crc)
> is _table[x], when x is the bit pattern of the modification (almost
> always 0xff)."

Great remarks. Will update the code.

> Thanks!

Thanks.

Gr. AvS

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


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