Re: Using the GNAT defined attribute: 'Enum_Rep

["W. Wesley Groleau x4923" <wwgrol@pseserv3.fw.hac.com>]

> <<Is this true ?  Seems to me it's legal (though I've never seen
> it happen) for an implementation to generate anything it wanted
> for a representation as long as ordering, indexing, etc. worked.>>
> 
> No, not at all, the whole point of enumeration types is that this is the
> one place where Ada *does* have something to say about representation.
> The ACVC interpretation (and hence what all Ada compilers do), is that
> if you use an enumeration representation clause, then the representation
> must match that of integers of the same size.
> 
> And of course Pos and Val will NOT match representations assigned in
> this manner. Wes, if we believed your claim above, we would be believing
> that enumeration representation clauses have no runtime semantics. That
> is not the case!

Whoa!  Communication breakdown.  I said "is this true?" to someone's 
claim that the ABSENCE of an enum-rep-clause, makes the representation 
the same as the 'pos.  For most CPUs, making the internal rep.
the same as 'pos is probably the simplest and most efficient
approach.  But please cite LRM-83 or LRM-95 if it is illegal for
a compiler, given

  type Enum is (Zero, One, Two, Three, Four, Five, Six, Seven );

(with no rep-clause), please cite LRM-83 or LRM-95 if it is 
illegal for an implementation to internally use

  for Enum use (Zero  => 2#00000001#,
                One   => 2#00000010#,
                Two   => 2#00000100#,
                Three => 2#00001000#,
                Four  => 2#00010000#,
                Five  => 2#00100000#,
                Six   => 2#01000000#,
                Seven => 2#10000000# );


-- 
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    Wes Groleau, Hughes Defense Communications, Fort Wayne, IN USA
Senior Software Engineer - AFATDS                  Tool-smith Wanna-be
                    wwgrol AT pseserv3.fw.hac.com

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