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From: kenny@uiucdcsb.CS.UIUC.EDU
Newsgroups: net.arch
Subject: Re: Re: 68k dbcc
Message-ID: <5600047@uiucdcsb>
Date: Tue, 6-May-86 16:35:00 EDT
Article-I.D.: uiucdcsb.5600047
Posted: Tue May  6 16:35:00 1986
Date-Received: Thu, 8-May-86 21:45:09 EDT
References: <133@cdx27.UUCP>
Lines: 34
Nf-ID: #R:cdx27.UUCP:133:uiucdcsb:5600047:000:1194
Nf-From: uiucdcsb.CS.UIUC.EDU!kenny    May  6 15:35:00 1986


/* Written  9:35 am  Apr 28, 1986 by jc@cdx27.UUCP in uiucdcsb:net.arch */
[...]
>Next they're going to make an add instruction that fails when either
>operand is zero, because "It's silly to waste time adding zero to a
>number."
[...]
>-- 
>	John Chambers
[...]
/* End of text from uiucdcsb:net.arch */

I don't know about adds, but early versions of the Honeywell Level 66
mainframe had a character string move instruction that caused a mysterious
machine fault (``illegal instruction,'' if memory serves) if the programmer
attempted to move a zero-length string.  Caused a lot of code looking like

	if (length isn't zero) move in to out.

all over the system.  Also caused some mysterious failures of tested code
(tested, that is, on newer machines) when it was installed on processors
that didn't have the fix for the bug.  

Once again, the rationale was that ``nobody in his right mind would ever try
to ...''

Kevin Kenny
University of Illinois at Urbana-Champaign
UUCP: {ihnp4,pur-ee,convex}!uiucdcs!kenny 
CSNET:	kenny@UIUC.CSNET
ARPA:	kenny@B.CS.UIUC.EDU	(kenny@UIUC.ARPA)

"Yes, understanding today's complex world is a bit like having bees live in
your head, but there they are."