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From: Robert Dewar <dewar@gnat.com>
Subject: Re: 3-bit array porting problem from ADA83 to GreenHills ADA95
Date: 1999/11/09
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Date: 1999-11-09T00:00:00+00:00
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In article <3827e839@pull.gecm.com>,
  "Steve Mossom" <stephen.mossom@gecm.com> wrote:
> It seems, from what I have read,
> that the ADA'95 LRM makes 'recommendations' to compiler
> vendors regarding their implementation in this area it does
> not really enforce any rules
> (quite rightly as it should not be implementation specific) .


This is not correct. The recommendations in chapter 13 become
requirements for a compiler that implements Annex C (Systems
Programming), and the ACVC tests do test these requirements.
You should only use a compiler that is 100% validated for
annex C for this kind of job (where rep clauses will be used).

It is the case that there are lots of things you would like to
work that are not requirements even if annex C is implemented.
The subject of this thread (3-bit packed arrays) is an example.

In GNAT, only a relatively small part of the rep clauses that we
implement are those required by the RM. We go far beyond these
minimum requirements. I suspect most/many/all? other Ada 95
compilers also go beyond the minimal requirements. Part of
acquiring an Ada compiler must be your effort to find out what
is implemented, and whether it will meet your needs.

In the case of GNAT, we were largely driven by old Ada 83
compilers, many of which implemented a very rich set of
representation clauses, and we tried to implement everything
we ran across in old Ada 83 legacy code, so that porting is
as simple as possible.

Robert Dewar
Ada Core Technologies


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