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From: Florian Weimer <fw@deneb.enyo.de>
Newsgroups: comp.lang.ada
Subject: Re: GNAT bug with respect to an Implementation Advise
Date: 13 Dec 2000 20:56:43 +0100
Organization: Enyo's not your organization
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Date: 2000-12-13T20:56:43+01:00
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"Jeff Creem" <jeff@thecreems.com> writes:

> The LRM has an implementation advice that says:
> 
> 13.13.2(17): Stream Oriented Attributes
> 
> If a stream element is the same size as a storage element, then the normal
> in-memory representation should be used by Read and Write for scalar
> objects. Otherwise, Read and Write should use the smallest number of stream
> elements needed to represent all values in the base range of the scalar
                                                 ^^^^^^^^^^
> type.

'base range' is crucial here.

> To which the GNAT RM says
> 
> Followed.

Correct.

> type My_Uint is range 0 .. 65535;
> for My_Uint'Size use 16;

My_Uint'Base'First is -2**31, and My_Uint'Base'Last is 2**31-1, I
think.

> The 'write on my_uint writes 32 bits not 16 bits. I realize that the
> 'write and 'size is an area where non-language lawyers get into
> trouble all the time but it sure seems to me as if GNAT is not
> following the IA.

GNAT is following the IA, but the IA is surprising.  There's also an
AI on this issue, which involved a lot of discussion.  (Some vendors
do not follow the IA and want to change the standard to officially
sanction the derivation, IMHO.