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From: bobduff@world.std.com (Robert A Duff)
Subject: Re: Portability of Arithmetic (was: Java vs Ada 95)
Date: 1996/10/16
Message-ID: <DzDBw3.ILH@world.std.com>#1/1
X-Deja-AN: 189808802
references: <325D7F9B.2A8B@gte.net> <ROGOFF.96Oct14095012@sccm.Stanford.EDU>
 <DzBrFw.IAs@world.std.com> <1996Oct15.174526.1@eisner>
organization: The World Public Access UNIX, Brookline, MA
newsgroups: comp.lang.ada
Date: 1996-10-16T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <1996Oct15.174526.1@eisner>,
Larry Kilgallen <kilgallen@eisner.decus.org> wrote:
>In article <DzBrFw.IAs@world.std.com>, bobduff@world.std.com (Robert A Duff) writes:
>> How about portability of arithmetic?  In Java, int is always exactly 32
>> bits 2's complement.  In Ada, Integer is whatever the machine supports.
>> And if I say "type T is range 1..100;" I might get 32-bit arithmetic, or
>> I might get 8-bit arithmetic, or who-knows-what.
>
>And why should it matter ?  If your specification is to cover that
>range, a compiler is meeting that specification even if it converts
>it to BCD to accomplish it on some _very_ old hardware.

   type T is range 1..100;
   X: T := ...;
   Y: T := ...;
   Average: T := (X + Y) / 2;

Because the above code will work fine on some Ada compilers, and blow up
on others (the addition will overflow using 8-bit signed arithmetic) if
X and Y happen to be, say, 99.  In Java, the above code is guaranteed to
work.

- Bob