Mega Code Archive
How to Calculate Easter Day for a specified year
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Title: How to Calculate Easter Day for a specified year
function Easter(Year: Integer): TDateTime;
{----------------------------------------------------------------}
{ Calculates and returns Easter Day for specified year. }
{ Originally from Mark Lussier, AppVision . }
{ Corrected to prevent integer overflow if it is inadvertently }
{ passed a year of 6554 or greater. }
{----------------------------------------------------------------}
var
nMonth, nDay, nMoon, nEpact, nSunday, nGold, nCent, nCorx, nCorz: Integer;
begin
{ The Golden Number of the year in the 19 year Metonic Cycle: }
nGold := (Year mod 19) + 1;
{ Calculate the Century: }
nCent := (Year div 100) + 1;
{ Number of years in which leap year was dropped in order... }
{ to keep in step with the sun: }
nCorx := (3 * nCent) div 4 - 12;
{ Special correction to syncronize Easter with moon's orbit: }
nCorz := (8 * nCent + 5) div 25 - 5;
{ Find Sunday: }
nSunday := (Longint(5) * Year) div 4 - nCorx - 10;
{ ^ To prevent overflow at year 6554}
{ Set Epact - specifies occurrence of full moon: }
nEpact := (11 * nGold + 20 + nCorz - nCorx) mod 30;
if nEpact 0 then
nEpact := nEpact + 30;
if ((nEpact = 25) and (nGold 11)) or (nEpact = 24) then
nEpact := nEpact + 1;
{ Find Full Moon: }
nMoon := 44 - nEpact;
if nMoon 21 then
nMoon := nMoon + 30;
{ Advance to Sunday: }
nMoon := nMoon + 7 - ((nSunday + nMoon) mod 7);
if nMoon 31 then
begin
nMonth := 4;
nDay := nMoon - 31;
end
else
begin
nMonth := 3;
nDay := nMoon;
end;
Easter := EncodeDate(Year, nMonth, nDay);
end; {Easter}
/mlussier
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