Refactored to use Julian Day Numbers internally.

Julian Day Numbers are the number of days which have elapsed since 24 November -4713 Gregorian.

The algorithm was published in the Communications of the ACM, volume 11, Number 10, October 1968.

See also:
http://www.magnet.ch/serendipity/hermetic/cal_stud/jdn.htm
http://www.cs.ubc.ca/spider/flinn/docs/scham/primitives/time.html

	arithmetic
	addDays: subtractDate: subtractDays:

	comparing
	< = hash

	converting
	asDate asGregorian asJulianDayNumber asSeconds month week

	inquiries
	dayOfMonth dayOfYear daysInMonth daysInYear daysLeftInYear firstDayOfMonth previous:

	obsolete
	day:year: firstDayOfMonthIndex: mmddyy

	printing
	mmddyyyy printFormat: printOn: printOn:format: storeOn:

	testing

	general inquiries
	dateAndTimeNow dayOfWeek: daysInMonth:forYear: daysInYear: firstWeekdayOfMonth:year: indexOfMonth: leapYear: nameOfDay: nameOfMonth:

	instance creation
	fromDays: fromJulianDayNumber: fromSeconds: fromString: new newDay:month:year: newDay:year: readFrom: today

	obsolete
	absoluteDaysToYear: yearAndDaysFromDays:into:

	accessing	top
	day Answer the day of the year represented by the receiver.
	julianDayNumber Answer the number of days (or part of a day) elapsed since noon GMT on January 1st, 4713 B.C.
	julianDayNumber: Set the number of days (or part of a day) elapsed since noon GMT on January 1st, 4713 B.C.
	leap Answer whether the receiver's year is a leap year.
	monthIndex Answer the index of the month in which the receiver falls.
	monthName Answer the name of the month in which the receiver falls.
	weekday Answer the name of the day of the week on which the receiver falls.
	weekdayIndex Monday=1, ... , Sunday=7
	year Answer the year in which the receiver falls.

	arithmetic	top
	addDays: Answer a Date that is dayCount days after the receiver.
	subtractDate: Answer the number of days between the receiver and aDate.
	subtractDays: Answer a Date that is dayCount days before the receiver.

	comparing	top
	< Answer whether aDate precedes the date of the receiver.
	= Answer whether aDate is the same day as the receiver.
	hash Hash is reimplemented because = is implemented.

	converting	top
	asDate
	asGregorian Return an array of integers #(dd mm yyyy)
	asJulianDayNumber
	asSeconds Answer the seconds between a time on 1 January 1901 and the same time in the receiver's day.
	month
	week

	inquiries	top
	dayOfMonth Answer which day of the month is represented by the receiver.
	dayOfYear
	daysInMonth Answer the number of days in the month represented by the receiver.
	daysInYear Answer the number of days in the year represented by the receiver.
	daysLeftInYear Answer the number of days in the year after the date of the receiver.
	firstDayOfMonth Answer the index of the day of the year that is the first day of the receiver's month.
	previous: Answer the previous date whose weekday name is dayName.

	obsolete	top
	day:year:
	firstDayOfMonthIndex: Answer the day of the year (an Integer) that is the first day of my month
	mmddyy Please use mmddyyyy instead, so dates in 2000 will be unambiguous

	printing	top
	mmddyyyy Answer the receiver rendered in standard fmt mm/dd/yyyy. Good for avoiding year 2000 bugs. Note that the name here is slightly misleading -- the month and day numbers don't show leading zeros, so that for example feb 1 1996 is 2/1/96
	printFormat: Answer a String describing the receiver using the argument formatArray.
	printOn: Append to the argument, aStream, a sequence of characters that identifies the receiver.
	printOn:format: Print a description of the receiver on aStream using the format denoted the argument, formatArray: #(item item item sep monthfmt yearfmt twoDigits) items: 1=day 2=month 3=year will appear in the order given, separated by sep which is eaither an ascii code or character. monthFmt: 1=09 2=Sep 3=September yearFmt: 1=1996 2=96 digits: (missing or)1=9 2=09. See the examples in printOn: and mmddyy
	storeOn: Append to the argument aStream a sequence of characters that is an expression whose evaluation creates an object similar to the receiver.

testing

top

	class initialization	top
	initialize Initialize class variables representing the names of the months and days and the number of seconds, days in each month, and first day of each month.

	general inquiries	top
	dateAndTimeNow Answer an Array whose first element is Date today and second element is Time now.
	dayOfWeek: Answer the index in a week, 1-7, of the day named dayName. Create an error notification if no such day exists.
	daysInMonth:forYear: Answer the number of days in the month named monthName in the year yearInteger.
	daysInYear: Answer the number of days in the year, yearInteger.
	firstWeekdayOfMonth:year: Answer the weekday index (Sunday=1, etc) of the first day in the month named mn in the year yr.
	indexOfMonth: Answer the index, 1-12, of the month monthName. Create an error notification if no such month exists.
	leapYear: Answer 1 if the year yearInteger is a leap year; answer 0 if it is not.
	nameOfDay: Answer a symbol representing the name of the day indexed by dayIndex, 1-7.
	nameOfMonth: Answer a String representing the name of the month indexed by monthIndex, 1-12.

	instance creation	top
	fromDays: Answer an instance of me which is dayCount days after January 1, 1901. Works for negative days before 1901. Works over a huge range, both BC and AD.
	fromJulianDayNumber:
	fromSeconds: Answer an instance of me which is 'seconds' seconds after January 1, 1901.
	fromString: Answer an instance of created from a string with format DD.MM.YYYY.
	new Return a constant, or date today?
	newDay:month:year: Arguments day, month and year are all integers, except month may be a string. For compatibility, two digit dates in the range 00..49 are from 2000, 50..99 from 1900. Please use ALWAYS four digits year numbers.
	newDay:year: Answer an instance of me which is dayCount days after the beginning of the year referenceYear.
	readFrom: Read a Date from the stream in any of the forms: <day> <monthName> <year> (5 April 1982; 5-APR-82) <monthName> <day> <year> (April 5, 1982) <monthNumber> <day> <year> (4/5/82)
	today Answer an instance of me representing the day and year right now.

	obsolete	top
	absoluteDaysToYear: Computes the number of days from (or until) January 1 of the year 1 A.D. upto (or since) January 1 of a given year. [Alan Lovejoy]
	yearAndDaysFromDays:into: Compute the Gregorian year, and the day of the year, from the number of days since (or until) January 1 of the year 1 A.D. Return the values in a block. [Alan Lovejoy]