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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Confusing language,
 was Re: Help help.. please.i am totaly new in ada programing
Date: 1999/11/12
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In article <wcc4ses3kmn.fsf@world.std.com>,
  Robert A Duff <bobduff@world.std.com> wrote:
> I disagree.  It is possible to define a binary representation
> that is still standard and portable.

Well that's pretty tricky, because of 1's complement vs
2's complement problems (a VERY VERY hot issue given the
Univac/Unisys presence here -- you may remember that this
fuss appeared even in the context of the Ada design years
later), and because of the endianness issues (complicated
by the Marc Williams patent).

The fact that no language has done this (certainly Ada did not
even attempt this) indicates that it is not trivial to do this
at all.

> For example, the standard stream data in Ada is
> nowhere near being portable!
>
> Right, and I think that's bad.

Well you certainly would not want to *mandate* that the stream
format be portable (you will run into all kinds of difficulties
if you do this, not least of which is serious inefficiencies
on some machines). As you know, GNAT provides the option of
using XDR for streams, which is useful in two contexts:

1. Allowing creation of distributed programs using Annex E
facilities that allow mixed platform communication.

2. Implementing passive partitions (which in GNAT provide
interprogram communication and persistence, as well as the
standard Annex E uses) in a manner that is platform independent.
For example, you can run a program on Solaris with a package
full of data, and then when you later run a program referencing
this same package on x86/Linux, you pick up the same data values
that existed at he time of termination of the Solaris program.

Both of which are really neat and useful features, but they come
at quite a price in efficiency.

P.S. I think it would be nice if other Ada 95 vendors would
provide the option of using XDR for streams as well, allowing
inter-compiler compatibility.


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