Path: utzoo!attcan!uunet!mcvax!hp4nl!bebux!henk
From: henk@bebux.UUCP (Henk Dijkstra)
Newsgroups: comp.sys.ibm.pc
Subject: Re: CRC checksums
Keywords: CRC checksums computation algorithms
Message-ID: <1528@bebux.UUCP>
Date: 12 Jan 89 21:18:03 GMT
References: <5303@phoenix.Princeton.EDU>
Reply-To: henk@bebux.UUCP (Henk Dijkstra)
Organization: Betronic B.V.	AMSTERDAM	Netherlands
Lines: 31

In article <5303@phoenix.Princeton.EDU> jwbirdsa@phoenix.Princeton.EDU (James Webster Birdsall) writes:
>
>   Can somebody either tell me or point me to references on how to
>compute a CRC checksum for a block of characters? Fast algorithms would
>be much appreciated. :-)
>   Thanks...

Here is an Outline:
* This is a parallel CRC-computing function
* For a 8-bit CRC you could use a generator polynome of: X8 + X4 + X3 + 1
* Or 19H (X4+X3+1) X8=carry.
* 
START:
	CRC-Reg = 0
LOOP:
	shift left CRC-Reg for 1 position
	Was the MSB of CRC-Reg clear? (Carry=0?)
		THEN   EXOR CRC-Reg with Polynome (19H)
	EXOR CRC-Reg with memory cell
	Was last memory cell done?
		NO  increment memory pointer by 1 and goto LOOP:
		YES CRC now in CRC-Reg.


From: D.Leisengang; Signaturanalyse in der Datenverarbeitung.

-- 
Henk Dijkstra	: BETRONIC B.V.			USENET : henk@bebux.UUCP
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