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From: "Randy Brukardt" <randy@rrsoftware.com>
Newsgroups: comp.lang.ada
Subject: Re: Quality systems (Was: Using Ada for device drivers? (Was: the
   Ada mandate, and why it collapsed and died))
Date: Thu, 22 May 2003 16:15:05 -0500
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Date: 2003-05-22T16:15:05-05:00
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Robert A Duff wrote in message ...
>Vinzent Hoefler <ada.rocks@jlfencey.com> writes:
>> Currently this thing is written in assembly language, but if I'd ever
>> reengineer that in Ada I'd definitely use a (non-binary) modular type
>> for the index then (and an array with 16 entries instead). Of course,
>> as you pointed out, I could do the modulo arithmetic by hand, but why
>> if I can let the compiler handle it?
>
>Because it makes the code easier to understand if the "mod" is
explicit.


I agree, especially because the generated code for modular types is
ugly.

My personal opinion is that wrap-around semantics for unsigned types is
a mistake. Ada is about safety, and there is no safety in 2+2=1. I
thought and still think that we should have added unsigned integer types
with overflow, and then had a special package with wrap-around types of
the full sizes for those rare cases where you need such functionality.

Virtually every time I use a modular type, I end up tracking down some
bug at runtime that would have been caught had there been an overflow
check. (Typically in the creation of an array index or the like.) Most
of the these types are 'indexes' (handles) that have to fit in a
particular size, and I often write checks like:
    if Index-1 > 0 then
        Index := Index - 1;
    end if;
which is wrong for a modular type. (Consider Index=0).

                         Randy.