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From: Guillaume <guifo@wanadoo.fr>
Newsgroups: comp.lang.ada
Subject: Re: First time Ada has let me down
Date: Thu, 26 Oct 2000 22:27:57 +0000
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Jeff Carter wrote:

> Shifty wrote:
> >   function Calculate_Ip_Header_Length
> >              (Byte_At : in System.Address) return Integer is
> 
> It's extremely rare to need to use addresses in all-Ada code except when
> dealing with hardware, even in Ada 83. It generally indicates either a
> poor design or a lack of understanding of the capabilities of the
> language.

Agreed !
Aliasing effective parameters is not a good way to employ the "use at" 
clause, as it may break program execution especially with optimization 
options turned on. I've experienced this myself, the compiler I use at work 
produces executables which raise program_error on such code. I've not 
investingated a lot but with a procedure with a small enough effective 
parameter, the compiler I use seems to copy this parameter in a CPU 
register making the "use at" clause totally wrong !

I may seem to repeat here but ... the RM is your friend ...

"Address clauses should not be used to achieve overlays of objects or 
overlays of program units. Nor should a given interrupt be linked to more 
than one entry. Any program using address clauses to achieve such effects 
is erroneous."

Point your browser to :

http://www.adahome.com/LRM/83/RM/rm83html/lrm-13-05.html#13.5

        Guillaume