Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!apple!usc!ucsd!ucbvax!decwrl!decvax!ima!cfisun!lakart!dg
From: dg@lakart.UUCP (David Goodenough)
Newsgroups: comp.sources.wanted
Subject: How to turn a CRC table back into the old shift/xor method
Message-ID: <669@lakart.UUCP>
Date: 25 Aug 89 02:24:25 GMT
Reply-To: dg@lakart.UUCP (David Goodenough)
Organization: Lakart Corporation - The ultimate in broadcast automation
Lines: 19

The "hip" method for doing CRC evaluation nowadays is to use one of these
table driven beasties. However, in a 32 bit environment, the table requires
1K. Given that I am working in a situation where memory is a premium item,
I would like to sacrifice speed for size. The stock way of doing CRC is:

	xorflag = most_significant_bit_of_crc_value;
	crc_value += crc_value + new_bit;
	if (xorflag)
	  crc_value ^= some_constant;

for each bit in the data. Can I assume that the "some_constant" is the first
non-zero value in the array? Any other "gotcha's" I should watch for?

		Thanks in advance,
-- 
	dg@lakart.UUCP - David Goodenough		+---+
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