How to add exactly one year-1 day to date in Firebird procedure or query? I have to calculate a year period from certain date, for example: 01.05.2002 -> 30.04.2003.

when I do simply: date+364 it works well in most cases, but there is a problem with leap years.

I found a function from internet to check for leap year:

CREATE PROCEDURE IS_LEAPYEAR (
D TIMESTAMP
) RETURNS (
LY INTEGER
) AS
BEGIN
IF ( 2 = EXTRACT(MONTH FROM (D - EXTRACT(YEARDAY FROM D) + 59)) ) THEN
LY = 1; /* leap year */
ELSE
LY = 0; /* normal year */
END


but when I try:
SELECT * FROM IS_LEAPYEAR('27.04.2003');

returned is 'null'.

any ideas?