Easter date algorithms (c) Henk Reints

Use this algorithm | Gebruik deze algoritme

Algorithm of Oudin, described by Claus Tøndering. Source: http://www.tondering.dk/claus/calendar.html (For easier step by step calculation I have taken some steps "outside the parenthesis", i.e. steps D, E, K, P, and Q, which are encoded "inline" in Claus Tøndering's original).
Julian method (any year since A.D. 1)	Gregorian method (any year since 1583)
G = year MOD 19
	C = year DIV 100
	D = C - C DIV 4
	E = (8 x C + 13) DIV 25
I = (19x G + 15) MOD 30	H = (D - E + 19 x G + 15) MOD 30
	K = H DIV 28
	P = 29 DIV (H + 1)
	Q = (21 - G) DIV 11
	I = H - K x (1 - K x P x Q)
J = (year + year DIV 4 + I) MOD 7	J = (year + year DIV 4 + I + 2 - D) MOD 7
result = 28 + I - J

Use this algorithm | Gebruik deze algoritme

 

Next is a copy of the algorithm as Claus Tøndering shows it on his site in a more mathematical approach (also using integer division!), including the calculation of the correct month and day:

Easter date algorithms (c) Henk Reints