dateadd(datediff) equivalent in Oracle

Hi,

I have the following function in which I created in Sybase but need to convert to Oracle and having difficulty, Any help would be greatly appreciated.

CREATE FUNCTION "AFM"."BRG_DATEFIXED"(in int_type char(4), in interval integer, in datefirsttodo date, date_last_comp date)
--ALTER FUNCTION "AFM"."BRG_DATEFIXED"(in int_type char(4), in interval integer, in datefirsttodo date, date_last_comp date)
returns date
    begin
        declare returnVal date;
       
        if int_type = 'M' then
            set returnVal = dateadd(mm,(floor(datediff(mm,datefirsttodo,date_last_comp)/interval)+1)*interval,datefirsttodo)
        elseif int_type = 'YYYY' then
            set returnVal = dateadd(yy,(floor(datediff(yy,datefirsttodo,date_last_comp)/interval)+1)*interval,datefirsttodo)
        elseif int_type = 'ww' then
            set returnVal = dateadd(wk,(floor(datediff(wk,datefirsttodo,date_last_comp)/interval)+1)*interval,datefirsttodo)
        elseif int_type  = 'q' then
            set returnVal =dateadd(qq,(floor(datediff(qq,datefirsttodo,date_last_comp)/interval)+1)*interval,datefirsttodo)
        elseif int_type = 'd' then
            set returnVal = dateadd(dd,(floor(datediff(dd,datefirsttodo,date_last_comp)/interval)+1)*interval,datefirsttodo)
        end if;
        return(returnVal)
    end  Start Free Trial