Oracle Berechne Ostern

CREATE OR REPLACE FUNCTION eastern(yeartocalc NUMBER DEFAULT to_number(to_char(SYSDATE,'YYYY')))
    RETURN DATE
	IS RESULT DATE;
    a INTEGER;
    b INTEGER;
    c INTEGER;
    d INTEGER;
    e INTEGER;
    f INTEGER;
    g INTEGER;
BEGIN
    a := MOD(yeartocalc, 19);
    b := yeartocalc / 100;
    c := (8 * b + 13) / 25 - 2;
    d := b - (yeartocalc / 400) - 2;
    e := MOD(19 * MOD(yeartocalc, 19) + MOD(15 - c + d, 30), 30);
    IF e     = 28 THEN
        IF a > 10 THEN
            e := 27;
        END IF;
    ELSE
        IF e = 29 THEN
            e := 28;
        END IF;
    END IF;
    f := MOD(d + 6 * e + 2 * MOD(yeartocalc, 4) + 4 * MOD(yeartocalc, 7) + 6,7);
    g := e + f + 22;
    IF g > 31 THEN
        RESULT := to_date(g - 31
        || '.4.'
        || yeartocalc, 'DD.MM.YYYY');
    ELSE
        RESULT := to_date(g
        || '.3.'
        || yeartocalc, 'DD.MM.YYYY');
    END IF;
    RETURN(RESULT);
END eastern;