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From: "Shmuel (Seymour J.) Metz" <nospam@gsg.eds.com>
Subject: Re: Porting Experiences (was Ada and Pascal etc )
Date: 1997/11/04
Message-ID: <345F95D0.3984@gsg.eds.com>#1/1
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References: <34557f2b.1934172@news.mindspring.com>
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Organization: EDS MS
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Newsgroups: comp.lang.ada,comp.lang.c,comp.lang.c++
Date: 1997-11-04T00:00:00+00:00
List-Id: <comp.lang.ada>


Kaz Kylheku wrote:
> 
> That depends on how you look at it. I'd say that it requires a little
> more thought and skill to write portably with types that have sizes
> that are not fully specified, but it's not impossible.
> 
> C gives you a header, <limits.h>, which gives you the constants LONG_MIN
> and LONG_MAX. These tell you what the implementation's least and
> greatest values of type long are. These values are guaranteed to be
> at least -2^31+1 and 2^31-1 respectively.
> 
> If you assume that the long type has a range that is no larger than this,
> you are OK. If you write your code under the assumption that the
> range is LONG_MIN to LONG_MAX, you are also OK.
> 
> Sure, you might not be able to declare subtypes with more restricted ranges
> like in Ada, but that doesn't mean that portability has gone out the window!

So the portable way to declare 33-bit integers is to declare them as
long and let them be 128 bits on some machines? I don't consider that a
viable option. To restate, there is no portable way to cause the
compiler to chose a size that is the best compromise between the problem
requirements and the natural byte sizes of the machine.

In Ada I give a range of values and the compiler figures out whether to
use, e.g., words, half words or double words. In PL/I I give a number of
bits (for binary) or a number of digits (for decimal) and the compiler
figures it out. In C I have to play games with, e.g., multiple versions
of my headers. Unless and until the new standard passes, this aspect of
C will remain a serious blot on the claims of portability.

-- 

                        Shmuel (Seymour J.) Metz
                        Senior Software SE

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