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From: Martin <martin.dowie@btopenworld.com>
Newsgroups: comp.lang.ada
Subject: Re: Fun with C
Date: Sun, 17 Apr 2011 01:29:45 -0700 (PDT)
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Date: 2011-04-17T01:29:45-07:00
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On Apr 17, 8:17=A0am, Georg Bauhaus <rm.dash-bauh...@futureapps.de>
wrote:
> On 4/16/11 11:12 PM, Ludovic Brenta wrote:
>
> > "Nasser M. Abbasi"<n...@12000.org> =A0writes:
> >> $ gcc -Wall =A0t.c
> >> $ ./a.out
> >> R =3D 33554416
>
> > So R =3D 2**25 - 16, the correct answer is -16, so the actual result is
> > the correct one except for bit 24, which is 1 when it should be zero.
>
> > Out of curiosity, is this actual result a predictable consequence of th=
e
> > language definition, or is it undefined behavior?
>
> Why, it is the same in Ada.
>
> with Ada.Text_IO; use Ada.Text_IO;
> with Ada.Unchecked_Conversion;
>
> procedure Conv is
>
> =A0 =A0 =A0type UInt is mod 2**32;
> =A0 =A0 =A0type Int is range -2**31 .. 2**31 -1;
>
> =A0 =A0 =A0function To_UInt is new Ada.Unchecked_Conversion(Int, UInt);
> =A0 =A0 =A0N: UInt :=3D 128;
> =A0 =A0 =A0I: Int :=3D -2048;
> =A0 =A0 =A0R : Int;
> begin
> =A0 =A0 =A0R :=3D Int(To_UInt(I) / N);
> =A0 =A0 =A0Put_Line ("R =3D" & Int'Image(R));
> end;

Yes, the Ada version is _much_ more obvious and understandable

But I suspect the _intent_ is of the original code is (probably):

with Ada.Text_IO; use Ada.Text_IO;

procedure Conv is

     type UInt is mod 2**32;
     type Int is range -2**31 .. 2**31 -1;

     N: UInt :=3D 128;
     I: Int :=3D -2048;
     R : Int;
begin
     R :=3D I / Int (N);
     Put_Line ("R =3D" & Int'Image(R));
end;

-- Martin