home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!haven.umd.edu!darwin.sura.net!zaphod.mps.ohio-state.edu!cis.ohio-state.edu!ucbvax!WSMR-SIMTEL20.ARMY.MIL!WANCHO
- From: WANCHO@WSMR-SIMTEL20.ARMY.MIL ("Frank J. Wancho")
- Newsgroups: comp.os.cpm
- Subject: WANTED: Bit shift method for XMODEM packet check sum.
- Message-ID: <WANCHO.12809903647.BABYL@WSMR-SIMTEL20.ARMY.MIL>
- Date: 31 Aug 92 21:42:00 GMT
- Sender: usenet@ucbvax.BERKELEY.EDU
- Organization: The Internet
- Lines: 14
-
- 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
-