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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Ada and Java. different behaviour. casting long to int problem.
Date: 1999/06/17
Message-ID: <m3674n7427.fsf@mheaney.ni.net>#1/1
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References: <7jt2c0$vrb@drn.newsguy.com> <f92d7yyweva.fsf@eng.sun.com>
 <7k57vb$1ipf@drn.newsguy.com> <37667A00.2086E4F8@itools.symantec.com>
 <3767D597.8C77A423@cajunbro.com>
NNTP-Posting-Date: Wed, 16 Jun 1999 23:04:37 PDT
Newsgroups: comp.lang.ada,comp.lang.java.programmer
Date: 1999-06-17T00:00:00+00:00
List-Id: <comp.lang.ada>

On 16 Jun 1999 11:49, "George W. Bayles" <georgeb@cajunbro.com> wrote:

> That reminds me - using scaled integers to represent angles
> 
>   int theta = (int) MAX_INT*(theta_degrees/180.0); 
> 
> makes adding and subtracting angles much nicer because of the wrap
> around! It is a feature of computer integers that they are more like a
> compass than a ruler.

You can do this in Ada already:

  with System;
  package Angle_Types is

    type Angle_In_Deg_Type_Base is
      delta 1024.0 * System.Fine_Delta
      range -1024.0 .. 1024.0;

    for Angle_In_Deg_Type_Base'Small use
      1024.0 * System.Fine_Delta;

    subtype Angle_In_Deg_Type is
      Angle_In_Deg_Type_Base
      range 0.0 .. Angle_In_Deg_Type_Base'Pred (360.0);

    function "+" (L, R : Angle_In_Deg_Type)
      return Angle_In_Deg_Type;

    function "-" (L, R : Angle_In_Deg_Type)
      return Angle_In_Deg_Type;

    <other ops>

  end Angle_Types;


The addition and substraction operators are defined to have wrap-around
semantics.

This captures the angle abstraction perfectly, and we don't have to go
mucking around with hacks like "scaled integers."