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Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: comp.arch
Subject: Re: Wirth's "challenge" (was Re: RISC)
Message-ID: <8933@utzoo.UUCP>
Date: Sat, 14-Nov-87 21:49:13 EST
Article-I.D.: utzoo.8933
Posted: Sat Nov 14 21:49:13 1987
Date-Received: Sat, 14-Nov-87 21:49:13 EST
References: <1656@geac.UUCP> <863@winchester.UUCP> <197@m2.mfci.UUCP>, <902@mips.UUCP>
Organization: U of Toronto Zoology
Lines: 30
Keywords: RISC,array

> ... He mentioned items like undetected integer overflows...

Sigh, I note that the SPARC architecture, which looks like it's going to be
pretty popular, does not trap integer overflows.  (At least, I don't recall
it doing so -- I don't have the spec handy.)  Of course, it sets the good
old V bit, which you can check after every instruction if you don't mind the
performance penalty... meaning that nobody who cares about performance will
bother.  Sigh.

> ... For example, the lack of
> overflow checking and array bounds checking in C may have started as a
> reflection of the hardware architectures in place at the time...

No, not correct.  The "lack of overflow checking" is mythical -- C has
*never* promised that except for unsigned integers, which exist partly
for that specific purpose.  Many implementations don't check overflow,
and there is undoubtedly some code that depends on this, but this has
little or nothing to do with the language.  And array-bounds checking is
(a) a little difficult to reconcile with the explicit pointer-based
semantics of C's arrays, but nevertheless (b) possible in C, as witness
at least one debugging-oriented implementation I know of.

([mount soapbox] Besides, run-time checking for such things is the wrong
approach; no well-built program should ever do such things, and well-
builtness is something that ought to be checkable at compile time -- a
superior approach in every way except that implementation is harder
and not entirely understood yet.)
-- 
Those who do not understand Unix are |  Henry Spencer @ U of Toronto Zoology
condemned to reinvent it, poorly.    | {allegra,ihnp4,decvax,utai}!utzoo!henry