RAMSES	Systems Ecology
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DEFINITION MODULE DMClock;

  (*******************************************************************

    Module  DMClock     ('Dialog Machine' DM_V3.0)

      Copyright (c) 1990-2006 by Andreas Fischlin and ETH Zurich.

    Purpose   Access to the computer's internal clock to read
              the current time and date.

    Remarks   Macintosh implementation:
              ------------------------
              All date operations are only valid within range
              [1st January 1904 till 31st December 2040].
              Normally just the routines Today and Now are used.

              However, note also that a date and a time are stored
              in one long integer and this number corresponds to
              the number of seconds elapsed since 1st January 1904.
              This allows for easy and efficient date comparisons
              (e.g. when comparing file modification dates) but
              requires a routine for translation into more
              meaningful forms and vice versa. The latter is
              provided by the routines InterpreteSeconds and
              ConvertDateToSeconds.

              IBM PC implementation:
              ---------------------
              - to be completed -.

              This module belongs to the 'Dialog Machine'.


    Programming

      o Design
        Andreas Fischlin          21/09/1990

      o Implementation
        Andreas Fischlin          21/09/1990


    ETH Zurich
    Systems Ecology
    CHN E 35.1
    Universitaetstrasse 16
    8092 Zurich
    SWITZERLAND

    URLs:
        <mailto:RAMSES@env.ethz.ch>
        <http://www.sysecol.ethz.ch>
        <http://www.sysecol.ethz.ch/SimSoftware/RAMSES>


    Last revision of definition:  23/10/1990  AF

  *******************************************************************)


  CONST
    Jan = 1; Feb = 2; Mar = 3; Apr = 4; Mai = 5; Jun = 6;
    Jul = 7; Aug = 8; Sep = 9; Oct = 10; Nov = 11; Dec = 12;

    Sun = 1; Mon = 2; Tue = 3; Wed = 4; Thu = 5; Fri = 6; Sat = 7;

  (* hour is always within range [0..23] *)

  PROCEDURE Today (VAR year, month, day, dayOfWeek: INTEGER);
  PROCEDURE Now (VAR hour, minute, second: INTEGER);



  (*
    Low level routines for advanced programmers, mainly of use for
    the Macintosh implementation:
  *)
      PROCEDURE NowInSeconds (): LONGINT;
      (*
        Note above routine returns negative values since 19/Jan/1972
        03h14:07 UTC, since the range of LONGINT has been exhausted and
        seconds are now counted between MAX(LONGINT) and MAX(LONGCARD).
        Thus be aware of the fact that the more recent a time later than
        that date, the lower its value in seconds as returned by
        NowInSeconds.  if comparing or computing times it might be
        preferable to coerce first the returned value into a lcard value.
        Ex.:
              ConvertDateToSeconds(year1, ..., t1);
              ConvertDateToSeconds(year2, ..., t2);
              deltaT := LONGCARD(NowInSeconds()) + LONGCARD(t2) - LONGCARD(t1);
      *)
      PROCEDURE InterpreteSeconds  (secs: LONGINT;
                                    VAR year, month, day,
                                    hour, minute, second,
                                    dayOfWeek: INTEGER);
      PROCEDURE ConvertDateToSeconds (year, month, day,
                                     hour, minute, second: INTEGER;
                                     VAR secs: LONGINT);

END DMClock.