Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!pasteur!ucbvax!decwrl!sun!pitstop!sundc!seismo!uunet!mcvax!hp4nl!ruuinf!edwin
From: edwin@ruuinf.UUCP (Edwin Kremer)
Newsgroups: comp.unix.wizards
Subject: Re: new 4.3BSD Unix Internals book
Summary: The check algorithm is easy and I do remember although is
	 was some time ago for me too :-)
Keywords: ISBN
Message-ID: <1094@ruuinf.UUCP>
Date: 31 Jan 89 08:54:41 GMT
References: <568041@vaxa.uwa.oz> <362@microsoft.UUCP> <2248@unmvax.unm.edu> <9515@nsc.nsc.com>
Organization: Univ of Utrecht, Dept of CS
Lines: 36

In article <9515@nsc.nsc.com>, glennw@nsc.nsc.com (Glenn Weinberg) writes:
> In article <2248@unmvax.unm.edu> mike@turing.cs.unm.edu (Michael I. Bushnell) writes:
> >In article <362@microsoft.UUCP> w-colinp@microsoft.uucp (Colin Plumb) writes:
> >
> I don't remember the check algorithm off the top of my head.  Learned all
> this junk back in a computer science course a long time ago, believe it
> or not.
> 

The check algorithm for ISBN numbers is:

	check_isbn(isbn_nr)
	{
		mulfac = 1;			/* multiplication factor   */
		sum = 0;
		FOREACH digit in isbn_nr	/* start at leftmost digit */
		DO
			sum += digit * mulfac;
			++mulfac;
		DONE
		if ( sum % 11 == 0 )		/* can we divide by 11 ??  */
			return( TRUE );
		else return( FALSE );
	}


Needless to say this is rather sloppy code, but i hope it's clear
enough to get the point...
Please remember that the last 'digit' may be an 'X',
denoting a value of 10 !!!
							--[ Edwin ]--
-- 
Edwin Kremer, Department of Computer Science, University of Utrecht
Padualaan 14,  P.O. Box 80.089,  3508 TB  Utrecht,  The Netherlands
Phone: +31 - 30 - 534104        |  UUCP    : ...!hp4nl!ruuinf!edwin
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