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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Unconstrained base subtype questions
Date: Thu, 31 Mar 2011 14:10:55 -0700 (PDT)
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Date: 2011-03-31T14:10:55-07:00
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On Mar 31, 1:25=A0pm, "Alex Mentis" <f...@invalid.invalid> wrote:
> The following does not cause a constraint error in my version of GNAT
> on my system:
>
> ...
>
> Integer_Result :=3D (Integer'Last + Integer'Last) / 2;
>
> ...
>
> If I understand correctly, this is because the Integer operators are
> defined for operands of type Integer'Base, which is an unconstrained
> subtype and allows the operands to be stored in extended-length
> registers so that intermediate values in calculations do not overflow.

No, it's because all the operands are known at compile time and the
compiler can just figure out what the answer is.  There is no question
about "where operands are stored" or about how registers are used.
The code for this statement should not perform any addition or
division (or shift) operations.  See 4.9.

                            -- Adam