jtn@ADS.COM (John T. Nelson) (01/28/91)
>Newsgroups: comp.sys.mac.programmer >From: niko@iastate.edu (Schuessler Nikolaus E) >Subject: Writing a BinHex decoder > >I was trying to write a BinHex decoder (actually I successfully did), but >had a few questions: > > 1) How do you calculate the crc's? I thought a CRC was just a matter > of adding up all the bytes in the field to be checked, (I let > the integer wrap around when I added), but the crc is nowhere close > to what it's supposed to be. The files are decoded just fine, the > crc's just aren't checked. I think you're confused. What you've just described is a simple checksum, not a CRC. Cyclical Redunancy Checks are polynomial expansions and are MUCH more complicated. Check out a reference book on the subject sometime. You'll be amazed. You also won't understand at first glance why this thing actually works but that's okay... they do. -- ORGANIZATION: Advanced Decision Systems GEOGRAPHIC: Arlington, VA UUCP: kzin!speaker@mimsy.umd.edu INTERNET: jtn@potomac.ads.com SPOKEN: John T. Nelson PHONE: (703) 243-1611