**on UK.MOD.RSRE** (*LAWS%rsre.mod.uk@NSS.Cs.Ucl.AC.UK*)

*Sun, 11 Oct 87 00:18*

**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]**Next message:**Rick Adams: "Re: RCTE"**Previous message:**Ron Natalie: "Re: DDN Backbone bandwidth vs. speed"

Vint,

I guess this reply should be to the John Robinson portion of your

msg - but my mailer is not that smart.

Concerning CRC checksum computation. More than 17 years ago I read a

paper on this topic which used matrix algebra to construct look-up

tables. You took your choice - one large table and a simple one

line equation, or more smaller tables and more complicated equations.

I could still remember enough maths then to follow the algebra

through and did a single table version for the CRC-16 checksum. I

used it in EIN and passed it around the European centres (there was

no chips then for this and most folks were having to do it in one-off

hardware of the day). My code implementation for a CTL Modular-One

(a UK m/c with some interesting inovations that were to appear in DEC

PDP 11) ran at 10 micro-secs per byte and only a little longer in

Corai-66. My only export of this to the US was Ed Cain about 2/3 years

ago.

What does suprise me is the steady rain of papers on this topic which

often propose less effective solutions (and also get the algorithm

wrong) and never reference this old paper. Just a mo......

....found it -

P E Boudreau and R F Steen

(IBM Corp, Research Triangle Park, N.C.)

Cyclic Redundancy checking by program.

AFIPS Conf Proc Vol.39 1971, pp 9-15

and the latest I just found this week and in my briefcase waiting

to be read

Georgia Griffiths and G Carlyle Stones

The tea-leaf reader algorithm: an efficient implementation of

CRC-16 and CRC-32.

Comms of the ACM July 1987 Vol.30 No.7 pp 617-620

typos: tbles = tables, Corai-66 = Coral-66

John

**Next message:**Rick Adams: "Re: RCTE"**Previous message:**Ron Natalie: "Re: DDN Backbone bandwidth vs. speed"

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