Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!sunybcs!bingvaxu!leah!itsgw!batcomputer!pyramid!voder!apple!bcase
From: bcase@apple.UUCP (Brian Case)
Newsgroups: comp.arch
Subject: Re: Wirth's "challenge" (overflows)
Message-ID: <6743@apple.UUCP>
Date: Sun, 15-Nov-87 21:10:14 EST
Article-I.D.: apple.6743
Posted: Sun Nov 15 21:10:14 1987
Date-Received: Tue, 17-Nov-87 02:27:34 EST
References: <1656@geac.UUCP> <863@winchester.UUCP> <197@m2.mfci.UUCP> <902@mips.UUCP> <8933@utzoo.UUCP>
Reply-To: bcase@apple.UUCP (Brian Case)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 33
Keywords: integeroverflow, European attitudes

Very early in the design of the Am29000, it was decided that instructions
for integer arithmetic would be provided in both trap-on-overflow and
no-trap-on-overflow versions.  Without question, the thrust behind this
decision came from Ole Moller, a Dane who has returned to his native
Denmark.  Ole was incredibly wonderful to work with:  he had a real grasp
of and desire for simplicity.  He also had a real sensitivity to run-time
checking.  I am not trying to pigeon-hole people or sound negative in any
way, but in general, I find that Europeans tend to have a real sympathy
for run-time checking.  I can't name one American, off the top of my
head, to whom I would attribute the same concern.  At least the concern
would not, to me, be the distinguishing feature that, to me, it so often
is in Europeans.  Ole also first suggested that the Am29000 have assert
instructions (many people can only think of them as "compare and trap"
but the effect is really "trap if assertion is false") to support Ada-like
constructs.  This group of instructions became the cornerstone of the
procedure-call mechanism we devised.

The Am29000 has probably got way too many add and subtract instructions;
while I was at AMD and making presentations to various groups, we got
plenty of strange looks and laughingly-said remarks like "What the hell
are these for?"  In at least one case, the most caustic remarks came from
some influential computer scientists.  Whatever you think of these
instrucdions, there is no incremental cost to trap 32-bit, two's complement,
integer arithmeitc overflow.

I guess the point is that while there is no less concern in America for
correct programs, run-time checking is much more acceptable to the
European mind-set.

I hope I haven't offended anyone.  Please feel free to set me straight
if I deserve to be so set.  I heard Wirth speak at ASPLOS, and although
I really don't agree with him, I thought that it was good that he was
there to represent the "other side."  Comments?