93 lines
3.1 KiB
Plaintext
93 lines
3.1 KiB
Plaintext
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DEFINITION MODULE Calendar;
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(*
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This module defines a Date type and operations on dates of
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the Gregorian Calendar, introduced in 1582
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*)
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FROM DurationOps IMPORT
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Duration, Unit, UnitSet;
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FROM TimeDate IMPORT
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Time;
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TYPE Date =
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RECORD
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year : CARDINAL;
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month : [1 .. 12];
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day : [1 .. 31];
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hour : [0 .. 23];
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minute : [0 .. 59];
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second : [0 .. 59];
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thousandth: [0 .. 999];
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END; (* Date *)
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PROCEDURE GetMachineDate (VAR date: Date);
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(* Gets the machine date *)
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PROCEDURE SetMachineDate (date : Date);
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(* Sets the machine date *)
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PROCEDURE TimeToDate (time : Time;
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VAR date : Date);
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(* Type conversion from Time (in TimeDate) to Date (in Calendar) *)
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PROCEDURE DateToTime (date : Date;
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VAR time : Time);
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(* Type conversion from Date (in Calendar) to Time (in TimeDate) *)
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PROCEDURE IsValid (date : Date): BOOLEAN;
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(* Returns TRUE if date is valid, according to the Gregorian calendar *)
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PROCEDURE DaysIn (month : CARDINAL;
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year : CARDINAL): CARDINAL;
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(* Returns the number of days in the month of the year, according to
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the Gregorian calendar, 0 if month is out of range. *)
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PROCEDURE LeapYear (year : CARDINAL): BOOLEAN;
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(* Returns TRUE if year is a leap year, according to the Gregorian
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calendar (year number divisible by 400 or by 4 and not by 100) *)
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PROCEDURE SameDate (date1, date2 : Date;
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precision : Unit) : BOOLEAN;
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(* Returns TRUE if date1 and date2 are the same date, within precision *)
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PROCEDURE Later (date1, date2 : Date;
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precision : Unit) : BOOLEAN;
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(* Returns TRUE if date1 comes after date1, within precision *)
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PROCEDURE LaterOrSameDate (date1, date2 : Date;
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precision : Unit) : BOOLEAN;
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(* Returns TRUE if date2 is after date1 or if date1 and date2 are the same
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date, within precision *)
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(* The following operations give good results only with dates following
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October 15, 1582; when the Gregorian Calendar was first used.
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Accuracy to the second over long periods cannot be achieved, due to
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fluctuations in the Earth rotation that often cause annual corrections
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of one second. *)
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PROCEDURE AddToDate (date : Date;
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duration : Duration;
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VAR resultDate : Date);
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(* Add a duration to a date, gives a new date *)
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PROCEDURE SubToDate (date : Date;
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duration : Duration;
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VAR resultDate : Date);
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(* Subtract a duration from a date, gives a new date *)
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PROCEDURE DeltaDate (date1, date2 : Date;
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unitFormat : UnitSet;
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VAR duration : Duration);
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(* Absolute value of the difference between two dates, given a duration
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with units in unitFormat (see module Duration) *)
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END Calendar.
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