hood@uiucuxc.UUCP (11/20/84)
Is there anyone out there who can help me find a reasonable algorithm for the CRC error checking scheme? I have seen somewhere that the "formula" is n^16 + n^12 + n^5 + 1 for the 2 CRC bytes found on floppy disk formats. I need a formula compatible with XMODEM protocol. Is it the same one? If so what am I doing wrong... thanx E. Gray
hugh@hcrvax.UUCP (Hugh Redelmeier) (11/21/84)
There are several standard CRC formulae; CRC is a kind of hash
("Cyclic Redundancy Check"). It is easily computed using a
shift register with feedback; how it is connected determines the
formula. The two popular standards are called CRC16 and CCITT.
Further complication: sometimes the initial value for the shift
register is all-zeros, sometimes all-ones!
The "CRC" used in some later xmodems is not a CRC at all, but some
other hash!
See my submission to net.sources last Thursday.