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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang.c
Subject: Re: integer types
Message-ID: <2950@umcp-cs.UUCP>
Date: Fri, 1-Feb-85 14:26:12 EST
Article-I.D.: umcp-cs.2950
Posted: Fri Feb  1 14:26:12 1985
Date-Received: Sun, 3-Feb-85 09:07:21 EST
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Organization: U of Maryland, Computer Science Dept., College Park, MD
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Actually, there are a couple of different problems to be solved, and
subranges don't seem to be the right solution for all of them.

1.  You want a variable whose value is to always be contained within
    some particular range (e.g., array indicies).  Subrange types
    (especially runtime-checked types) are nice.

2.  You want a variable whose value can be in *at least* some particular
    range.  Here subrange types that *are not* checked at run time
    seem to work well (though if there is no checking, calling it a
    subrange seems misleading, to me).

3.  You want a variable whose value is in the largest possible range.
    Here subranges fail miserably, because you can't write
    [-infinity..infinity], and even if you could, the machine probably
    wouldn't support *that* (we won't mention lisp bignums).  If you
    have a ``minint'' and ``maxint'' that might work, but perhaps the
    machine can (with some speed degradation perhaps) support something
    bigger than ``integers''.

Anyway, subranges have their uses.  But since C hasn't got subranges,
if you want (1) or (2), use typedefs, preferably in machine-dependent
header files.  In fact, typedefs will work for (3) also.  So why aren't
you using them?  :-)
-- 
(This line accidently left nonblank.)

In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7690)
UUCP:	{seismo,allegra,brl-bmd}!umcp-cs!chris
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