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

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Message-ID: <20110524225224.32163.qmail@science.horizon.com>
Date:	24 May 2011 18:52:24 -0400
From:	"George Spelvin" <linux@...izon.com>
To:	akpm@...ux-foundation.org, arend@...adcom.com
Cc:	error27@...il.com, linux-kernel@...r.kernel.org,
	linux-wireless@...r.kernel.org, linux@...izon.com,
	linville@...driver.com
Subject: Re: [RFC] lib: crc8: add new library module providing crc8 algorithm

> 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.

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.

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)."

Thanks!
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