Path: utzoo!attcan!uunet!husc6!bloom-beacon!spdcc!ima!haddock!karl
From: karl@haddock.ima.isc.com (Karl Heuer)
Newsgroups: comp.lang.c
Subject: Re: Numerical Recipes is non-portable code
Message-ID: <7142@haddock.ima.isc.com>
Date: 7 Sep 88 20:07:20 GMT
References: <564@accelerator.eng.ohio-state.edu>
Reply-To: karl@haddock.ima.isc.com (Karl Heuer)
Organization: Interactive Systems, Boston
Lines: 17

rob@kaa.eng.ohio-state.edu (Rob Carriere) writes:
>marv@ism780.UUCP (Marvin Rubenstein) writes:
>>[In a hypothetical extended C, with arrays x[5:49] and y[0:44], and an
>>integer variable i, the accesses `x[i]' and `y[i-5]' should generate the
>>same code on a reasonable compiler.]
>
>Actually, a reasonable compiler would probably generate better code for
>k=x[i]; because it cannot do the optimization I'm trying to manually make
>either: illegal pointer!

If the architecture in question is "normal", then the compiler *is* free to do
that optimization.  If the hardware will fault on the mere mention of an
illegal pointer, then it can't optimize it -- but how do you think it's going
to implement z=x[i], then?  They'll still generate the same code, but in this
case it'll be equally bad rather than equally good.

Karl W. Z. Heuer (ima!haddock!karl or karl@haddock.isc.com), The Walking Lint