NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/os/cpm/1073

Internet Message Format | 1992-08-30 | 1.8 KB

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From: [e-mail] (Dean Youngquist)
Newsgroups: comp.os.cpm,comp.os.msdos.programmer,comp.sys.ibm.pc.programmer
Subject: WANTED: Bit shift method for XMODEM packet check sum.
Message-ID: <[e-mail]>
Date: 30 Aug 92 19:57:44 GMT
Article-I.D.: leela.1992Aug30.195744.2256
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Organization: Computer Science Outreach Services - Oregon State University
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Nntp-Posting-Host: atlantis.cs.orst.edu

I'm looking for the bit shift method of obtaining the checksum used in the
XMODEM file transfer protocol.  I don't need any C or other high level
language code, and I already have the mathematical formula for obtaining
this sum but what I need is the fast way using registers in the 8088 CPU.


The reason I need this is that I'm trying to help out a friend with his BBS
system.  He does his own programming and since he is using an old XT for
a server and it handles multiple calls simultaneously, the poor machine
gets bogged down computing the checksum in a high level language (I don't
recall what language he is using, but it was something really obscure which
had excellent string handling capabilities.  Anyway he says the ting to do
is to put some numbers into the CPU reginsters directly, do some quick
shifting of something, and then out pops the checksum.  This would speed up
the system quite a bit I understand.

So if you have the CPU register method of getting the XMODEM checksum please
email it to me.

Thank you very much,

Dean Youngquist
FAX & Voice [phone]