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From: tbray@watsol.UUCP
Newsgroups: comp.arch
Subject: Word and subword sizes (24 bits, floats from hell)
Message-ID: <132@watsol.UUCP>
Date: Sun, 19-Jul-87 09:52:57 EDT
Article-I.D.: watsol.132
Posted: Sun Jul 19 09:52:57 1987
Date-Received: Tue, 21-Jul-87 00:56:29 EDT
References: <2792@phri.UUCP> <6705@steinmetz.steinmetz.UUCP> <524@ollie.UUCP> <2799@phri.UUCP>
Reply-To: tbray@watsol.waterloo.edu (Tim Bray)
Organization: New Oxford English Dictionary Project, U. of Waterloo, Ontario
Lines: 19
Summary: Harmless war stories

Roy Smith asked about ' a machine with a 24 bit word '.  At one point
GE made a line of such computers, called GEPAC.  They were aimed at process
control applicatins, and they had a couple at a steel company where I worked.
They ran off a real live drum.

Which reminds me of one of my favorite war stories.  The infamous old IBM 1130 
was basically a 16-bit machine.  For double precision it used this *6-byte*
ones-complement datum from *hell*.  While I was a hapless young DEC software 
services type, I had to write a subroutine which would convert such a beast 
to a VAX double.  When you do something like this, you realise you really don't 
understand anything about bit ordering or excess whatever notation.  (Consider 
what can happen to  numbers of the form -1 * (2**n) in a one's complement 
mantissa).  Anyhow, three days of MACRO 32 hacking later, I and the customer 
were happy.  Problem was, the reason we were doing this was to convert 10 
zillion numbers from old financials on tape.  When the accountants saw that 
all the historical figures were out by a penny or two for large dollar values, 
the you know what hit the you know what.  (Hey, you go from 6 to 8 bytes, 
change notation and FP formatting routines and see if the pennies come out 
right).  Never did find out how it ended.