Re: Integer overflow is int overflow (Re: Web browser in Ada)

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 27 Apr 2010 17:30:44 +0200, Georg Bauhaus wrote:

> My conclusions would be that:
> 
> Standard.Integer is a constrained subtype. Its objects are
> not like (what is commonly known as) integers, a set that can
> be extended at will.

The set of integers is not extensible "at will." You probably meant that
for any integer there exists at least one [actually an infinitely countable
set] of greater or lesser integers. Nevertheless the set of integers (Z) is
fixed.

Standard.Integer is not an integer, it is a type, used to model integers or
other entities. It is not Z independently on how adequately it models the
latter.

> They cannot overflow in Ada mode.  There is no wrap-around.

> Named numbers of no-name type universal_integer
> cannot overflow, their value is determined by the compiler,

Their behavior, you mean. The value is determined by the expression and the
language rules.

> they are not objects, and they can hit compiler capacity limits.

Whether they are [run-time] objects is up to compiler. The compiler in Ada
has certain freedom to "objectize" and "deobjectize" things.

> So neither Standard.Integer nor universal_integer is an integer.

See above. They are not per definition. The question how adequately they
can model Z, is answered as: neither does it 100%. The domain of either
type is finite. Both domains include non-integer ideal elements called
"exception propagation" or "compile error." Concerning the latter, for any
legal Ada program there can exist a compiler capable to compile it without
error [if you have enough material and time].

> Nor is C's int.  Still assuming C's int is like integers,
> encouraged by how "int" and "integer" are used interchangeably
> in talks and writings, leads to to overflow (this is my
> hypothesis).

You need overflow in order to define the behavior of the operations closed
only in Z. E.g. "+".

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de