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I studied CRC's in my communications class, and CRC's have a pretty funny definition of 'divide'. It's long-division done in binary, but instead of binary subtractions in each stage it's binary exclusive-or. Explaining in detail would mean quoting from the book since I don't have the details memorized, so instead I'd reccomend you take a look at "Understanding Data Communications & Networks" by William A. Shay, 2nd ed, ISBN 0-534-95054-X. Really cool book.