Re: 83/95 issue, bad code or compiler bug

[matthew_heaney@acm.org (Matthew Heaney)]

In article <jeffrey.m.creem-1911981641480001@ljd155.sanders.lmco.com>,
jeffrey.m.creem@lmco.com (Jeff Creem) wrote:

>type My_Integer_Type is range -2**31 .. 2**31-1;
>for My_Integer_Type'size use 32;

Please use the types in package Interfaces; either Interfaces.Integer_32 or
Interfaces.Unsigned_32.  

>subtype My_Subtype is My_Integer_Type range 0 .. 255;
>
>
>type My_Record is
>  record
>    My_Field    : My_Subtype;
>    Other_Field : My_Integer_Type;
>  end record;
>
>for My_Record use
>  record
>    My_Field    at 0 range 0 .. 31;
>    Other_Field at 4 range 0 .. 31; 
>  end record;
>
>for My_Record'size use 2 * 32;
>

This is bad style.  For low-level I/O --here, meaning anything that appears
as the component of a record with a rep clause-- all scalar types should
have no constraints.  In your example, My_Field should be of type
My_Interger_Type (Interfaces.Integer_32), not My_Subtype.

>Is this due to the Ada 83 code being written in a poor totally unportable way,
>or is this permitted and expected in Ada 95 or is this a compiler bug (GNAT
>does not exhibit this "bad" behaviour on my code but it certainly could
>be that the code as written will have implementation defined results).

Don't mix rep clauses and types-with-constraints.