Add EASTERSUNDAY function

Move EASTERSUNDAY from the Huge group to the Large group.

Define as:

Syntax: EASTERSUNDAY( [Number Year] )
Description: Returns the date of Easter Sunday in the Gregorian Calendar in the year passed in as Year if given, otherwise returns the date of the next Easter Sunday on or after TODAY().  Note: The use of the Gregorian calendar was introduced in different locations at different times.

Return: Date

Constraints: 1582 <= Year <= 9956

Semantics: Given a value for Year, the Easter Sunday date is calculated according to the following algorithm given an integer Year in the range from 1582 to 9956:

A1 = INT(Year/100)
A2 = Year-19*INT(Year/19)
A3 = INT((A1-17)/25)
A4 = MOD(A1-INT(A1/4)-INT((A1-A3)/3)+19*A2+15;30)
A5 = A4-INT(A4/28)*(1-INT(A4/28)*INT(29/(A4+1))*INT((21-A2)/11))
A6 = MOD(Year+INT(Year/4)+A5+2-A1+INT(A1/4);7)
A7 = A5-A6
month = 3+INT((A7+40)/44)
day = A7+28-31*INT(month/4)

The resulting date is: DATE(Year;month;day).

If Year is not given, the above calculation is performed for the current and the next year and the smaller of the two dates is returned that is not before TODAY().

Updated as resolved on 11/Sep/23: contraint on earliest year changed from '1582' to 1583':

6.10.8 EASTERSUNDAY

Summary: Returns the date of Easter Sunday in the Gregorian Calendar in Year if given, otherwise returns the date of the next Easter Sunday on or after TODAY().

Note: The use of the Gregorian calendar was introduced in different locations at different times.

Syntax: EASTERSUNDAY( [ Integer Year ] )

Returns: Date

Constraints: 1583 ≤ Year ≤ 9956

Semantics: Given an integer value for Year in the allowed range, the Easter Sunday date is calculated according to the following algorithm:

A1 = INT(Year/100)
A2 = Year-19*INT(Year/19)
A3 = INT((A1-17)/25)
A4 = MOD(A1-INT(A1/4)-INT((A1-A3)/3)+19*A2+15;30)
A5 = A4-INT(A4/28)*(1-INT(A4/28)*INT(29/(A4+1))*INT((21-A2)/11))
A6 = MOD(Year+INT(Year/4)+A5+2-A1+INT(A1/4);7)
A7 = A5-A6
month = 3+INT((A7+40)/44)
day = A7+28-31*INT(month/4)

The resulting date is: DATE(Year; month; day).

If Year is not given, the above calculation is performed for the current and the next year, and the smaller of the two dates that is not less than TODAY() is returned.