Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!uflorida!novavax!proxftl!bill
From: bill@proxftl.UUCP (T. William Wells)
Newsgroups: comp.lang.c
Subject: Re: "Numerical Recipes in C" is nonportable code
Message-ID: <656@proxftl.UUCP>
Date: 29 Aug 88 06:19:02 GMT
References: <664@lindy.Stanford.EDU> <6758@megaron.arizona.edu> <718@gtx.com> <13258@mimsy.UUCP> <531@accelerator.eng.ohio-state.edu>
Reply-To: bill@proxftl.UUCP (T. William Wells)
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In article <531@accelerator.eng.ohio-state.edu> rob@kaa.eng.ohio-state.edu (Rob Carriere) writes:
: In article <13258@mimsy.UUCP> chris@mimsy.UUCP (Chris Torek) writes:
: > [ still on the b = malloc( foo );  bb = b - 1; code in NumRecipes ]
: >Such an implementation will ABORT ON THE COMPUTATION `b - 1',
: >possibly (indeed, preferably) at compile time.  And it is legal!
:
: So the standard says, they tell me.  It is also one the more flagrant
: violations of the Principle of Least Astonishment I've seen in a
: while.

Actually, on a segmented architecture I might be astonished if it
*didn't* bomb.  The principle is rather subjective I'm afraid.

:         In fact, while we're at it, it would seem to violate the idea
: that you give the programmer all the rope she asks for, because she
: just might be needing it to pull herself out of a bog.

Note that the standard does *not* say that you can't do this, it
just says that it is nonportable.  So, unless this bog is a
portable bog, she (Ugh. I prefer s/h/it for a neutered pronoun :-)
won't need a portable rope!

:                                                         Gentlemen
: system programmers, surely you too have algorithms that are more
: accurately expressed with arrays from other than base zero?

Well, actually, no.  One of the characteristics of being *very*
experienced with a language is that you tend to think of
solutions in terms of what that language most easily supplies.

Hmmmm.  Now that I think about it, I do seem to recall some Shell
sort where a zero base made the code more complex.

However, since there *is* a portable way to do this (if you don't
mind the syntax), I'll show it.

func()
{
	int     foo_array[SIZE][SIZE];
#define foo(n,m)  (foo_array[(n)-1][(m)-1])
	...
}

Ugly, but it works.  And it can be used to make the NR programs
portable.

---
Bill
novavax!proxftl!bill