Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!utgpu!water!watmath!watsol!tbray 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.