Date   : Mon, 31 Aug 1992 15:42:00 MDT
From   : "Frank J. Wancho" <WANCHO@WSMR-SIMTEL20.ARMY.MIL>
Subject: WANTED: Bit shift method for XMODEM packet check sum.

Dean,

If you *really* meant "checksum," there is no algorithm - you simply
total the bytes of the packet and ignore the overflow, and the result
is the (8-bit) checksum.  But, nobody should be using "xmodem"
transfers with simple checksums; they should be using 16-bit CRCs at a
minimum.  (Idealy, they should be using the zmodem protocol with
32-bit CRCs.)

If you want to see how checksums and both types of CRCs are handled in
C, get a hold of a copy of the sources to RZ/SZ.  We have an anonymous
ftpable set in PD8:<MISC.ZMODEM> here.

--Frank


End of INFO-CPM Digest V92 Issue #89
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