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From: "Jerry van Dijk" <jvandyk@ibm.net>
Subject: Re: How to convert an Fixed_Point to to an Integer ?
Date: 1996/12/24
Message-ID: <01bbf179$0c4361e0$9b2d5c8b@jerryware>#1/1
X-Deja-AN: 205734162
references: <01bbf058$cbdbf980$LocalHost@jerryware>
 <1996Dec23.072835.1@eisner> <dewar.851351937@merv>
organization: *JerryWare HQ*, Haarlem, Holland
newsgroups: comp.lang.ada
Date: 1996-12-24T00:00:00+00:00
List-Id: <comp.lang.ada>



Robert Dewar <dewar@merv.cs.nyu.edu> wrote in article
<dewar.851351937@merv>...

> Well obviously Time is really a private type, so you are talking about
doing
> something very implementation dependent and nasty here.

Hmmmm, I don't know. The idea behind encapsulation is protecting the client
code
against changes in implementation, not preventing anyone to assign the
number of
seconds since the epoch to an Integer :-)

The real problem is that there is no conversion operation offered for the
type.

So I solved it by putting these conversion operation in a child of
Ada.Calender:

package Ada.Calendar.Posix is

   type Time_T is mod 2 ** Integer'Size;

   function Clock return Time_T;

   function To_Time (Date : Time_T) return Ada.Calendar.Time;
   function To_Time_T (Date : Ada.Calendar.time) return Time_T;

end Ada.Calendar.Posix;

package body Ada.Calendar.Posix is

   function Clock return Time_T is
   begin
      return To_Time_T (Ada.Calendar.Clock);
   end Clock;

   function To_Time (Date : Time_T) return Ada.Calendar.Time is
   begin
      return Ada.Calendar.Time (Date);
   end To_Time;

   function To_Time_T (Date : Ada.Calendar.Time) return Time_T is
   begin
      return Time_T (Date);
   end To_Time_T;

end Ada.Calendar.Posix;

> You will have to use Unchecked conversion to a type that has exactly the
> same range and delta as duration, you could use duration itself for this
> purpose.

Yes, but talking about messy...

> But really, you should ask yourself if you want to do this. The resulting
> code is highly non-portable and conceptually wrong.

Well, I am writing a more-or-less POSIX-like binding for use with
GNAT/DJGPP.
And that code is inherently non-portable anyway. On the other hand, it does
wonders for the portability of my code between GNAT/Linux and GNAT/DOS :-)

Thanks everyone, for the replies.

Jerry.

P.S. Although the newsfeed on jvdsys.nextjk.stuyts.nl is down, I can still
be
       reached there.