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Date: 21 Jul 93 16:38:58 GMT
From: eachus@mitre-bedford.arpa  (Robert I. Eachus)
Subject: Re: Can you help with fixed-point arithmetic?
Message-ID: <EACHUS.93Jul21113858@spectre.mitre.org>
List-Id: <comp.lang.ada>

    Art has explainded the reason for the CONSTRAINT_ERROR, now for
the solution(s).  The first is a pain, the second is non-portable, and
probably indicates a feature which can be added at low cost to Ada 9X.

    What you want to do is add days to times:

    with CALENDAR; use CALENDAR;
    ...
    function "+"(T: Time; Days: Integer) return Time is
      Y: Year_Number;
      M: Month_Number;
      D: Day_Number;
      S: Duration;
    begin
      Split(T,Y,M,D,S);
      -- do the arithmetic...
      return Time_Of(Y,M,D,S);
    end "+";

    -- the simpler solution is to peer into private parts.  SunAda:

    with Calendar;
    ...
    function "+"(T: Calendar.Time; Days: Integer) return Calendar.Time is
      type my_time is record -- lifted from calendar
           julian_day:    integer;    -- Julian Day Number
           sec:           duration;
      end record;
      function To_Mine is new UNCHECKED_CONVERSION(Time,My_Time);
      function To_Time is new UNCHECKED_CONVERSION(My_Time,Time);
      Input: To_Mine(T);
    begin
      Input.Julian_Day := Input.Julian_Day+Days;
      return To_Time(Input);
    end "+";

    In Ada_9X, it will be possible to extend Calendar with user
defined children, so the Unchecked conversions are unnecessary.
However, this particular function might make sense as an addition to
Calendar.



--

					Robert I. Eachus

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