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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Portability of Arithmetic (was: Java vs Ada 95)
Date: 1996/10/16
Message-ID: <dewar.845506499@merv>#1/1
X-Deja-AN: 189998325
references: <325D7F9B.2A8B@gte.net> <ROGOFF.96Oct14095012@sccm.Stanford.EDU>
 <DzBrFw.IAs@world.std.com> <1996Oct15.174526.1@eisner>
 <DzDBw3.ILH@world.std.com>
organization: New York University
newsgroups: comp.lang.ada
Date: 1996-10-16T00:00:00+00:00
List-Id: <comp.lang.ada>


Bob Duff said

   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."

I am not sure I understand Bob's statement here. The above code is certainly
not valid Java code, so what does it mean to say that the above code works
in Java. If you mean it is possible to write this in a manner that works
in Java, then the same statement can be made in Ada:

    type BT is range 1 .. 200;
    subtype T is BT range 1 .. 100;
    X : T := ...;
    Y : T := ...;
    Average : T := (X + Y)/2;

works fine. You can write invalid Ada code for anything, but doing so
does not prove anything!