a postgres function that convert Gregorian date to Jalali

g2j.sql

CREATE OR REPLACE FUNCTION g2j(in_date timestamp with time zone)
    RETURNS character varying AS
$BODY$
DECLARE
    aday        smallint;
    amonth      smallint;
    ayear       smallint;
    a1          char(4);
    b1          char(2);
    c1          char(2);
    Tday        smallint;
    Tmonth      smallint;
    Tyear       smallint;
    CabisehYear smallint;
    TMonthEnd   smallint;
    numdays     int;
    Const_Date  timestamp without time zone;
BEGIN
    Const_Date = cast('3/21/1921' as timestamp without time zone);
    numdays = DATE_PART('day', in_date - Const_Date);
    aday = 1;
    amonth = 1;
    ayear = 1300;
    CabisehYear = cast((numdays / 1461) as int);
    numdays = numdays - CabisehYear * 1461;
    Tyear = cast((numdays / 365) as int);
    If Tyear = 4
    then
        Tyear = Tyear - 1;
    end if;
    numdays = numdays - Tyear * 365;
    Tmonth = cast((numdays / 31) as int);
    If (Tmonth > 6)
    then
        Tmonth = 6;
    end if;
    numdays = numdays - Tmonth * 31;
    TMonthEnd = 0;
    If (numdays >= 30 And Tmonth = 6)
    then
        TMonthEnd = cast((numdays / 30) as int);
        If TMonthEnd >= 5
        then
            TMonthEnd = 5;
        end if;
        numdays = numdays - TMonthEnd * 30;
    End if;
    Tmonth = (TMonthEnd + Tmonth);
    Tday = numdays;
    Tyear = (Tyear + CabisehYear * 4);
    ayear = (ayear + Tyear);
    amonth = amonth + Tmonth;
    aday = aday + Tday;

    a1 = ayear;
    b1 = amonth;
    c1 = aday;


    If length(b1) = 1
    then
        b1 = '0' || b1;
    end if;
    If length(c1) = 1
    then
        c1 = '0' || c1;
    end if;
    return a1 || '-' || b1 || '-' || c1;
END;
$BODY$
    LANGUAGE plpgsql
    VOLATILE
    COST 100;