Oracle Berechnen der Zeit zwischen zwei DATE Spalten

Um die Zeit zwischen zwei Spalten des Types DATE zu messen, habe ich folgende Funktion geschrieben.

Skript (kurz):

create or replace function dbw.datediff
                                 ( d    date, 
                                   c    date)
    /***************************************************************************
     * Created.... : 2016-04-28
     * Author..... : Lenzin Marc
     * Description : Time Between 2 Dates
     * Parameter.. : d (date):      Last Date
     *               c (date):      First Date
     ***************************************************************************/ 
return varchar2 is ret varchar2(100);

begin
  -- Check dates
      if    d is null 
         or c is null 
            then raise_application_error(-20101, 'NULL Value is not allowed');
      end if;
  
  ret  := floor(((d-c)*86400)/3600)||'h '||
          lpad(floor((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600)/60),2,'0')||'m '||
          lpad(round((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600-(floor((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600)/60)*60))),2,'0')||'s';
  
  return ret;
end datediff;

-- TEST:
-- Zeit zwischen zwei Dates
    select dbw.datediff(trunc(sysdate),sysdate+1/3600) test 
    from dual;
/

Skript (Lang):

create or replace function dbw.datediff
                                 ( d    date, 
                                   c    date     default sysdate,
                                   m    number   default 1,
                                   a    varchar2 default null,
                                   h    varchar2 default null,
                                   i    varchar2 default null,
                                   s    varchar2 default null)
    /***************************************************************************
     * Created.... : 2016-04-28
     * Author..... : Lenzin Marc
     * Description : Time Between 2 Dates
     * Parameter.. : d (date):      Last Date
     *               c (date):      First Date
     *               m (number):    Output Format
     *                                1:  Short..: ?h ??m ??s
     *                                2:  DE: ? Stunden ?? Minuten ?? Sekunden
     *                                22: EN: ? Hours ?? Minutes ?? Seconds
     *                                3:  Clock..: ?:??:??
     *                                4:  Custom Delemiter (Parameterh,i,s)
     *              a (varchar2):   Custom Placeholder before hours
     *              h (varchar2):   Custom Delemiter between hours and minutes
     *              i (varchar2):   Custom Delemiter between minutes and seconds
     *              s (varchar2):   Custom Placeholder after Seconds
     ***************************************************************************/ 
return varchar2 is 
    ret         varchar2(100);
    f_hh        varchar2(10);
    f_mi        varchar2(10);
    f_ss        varchar2(10);
    r_hh        varchar2(6);
    r_mi        varchar2(2);
    r_ss        varchar2(2);
    
begin
  -- Check dates
      if    d is null 
         or c is null 
            then raise_application_error(-20101, 'NULL Value is not allowed');
      end if;
  
  -- Define Output Format
      if    m = 1  then f_hh := 'h ';        f_mi := 'm ';        f_ss := 's ';
      elsif m = 2  then f_hh := ' Stunden '; f_mi := ' Minuten '; f_ss := ' Sekunden';
      elsif m = 22 then f_hh := ' Hours ';   f_mi := ' Minutes '; f_ss := ' Seconds';
      elsif m = 3  then f_hh := ':';         f_mi := ':';         f_ss := '';
      elsif m = 4  then f_hh := h;           f_mi := i;           f_ss := s;
      end if;

  r_hh := floor(((d-c)*86400)/3600);
  r_mi := floor((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600)/60);
  r_mi := lpad(r_mi,2,'0');
  r_ss := round((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600-(floor((((d-c)*86400)-floor(((d-c)*86400)/3600)*3600)/60)*60)));
  r_ss := lpad(r_ss,2,'0');

  ret :=    r_hh||f_hh||
            r_mi||f_mi||
            r_ss||f_ss;
  
  if m=4 
    then ret := a||ret; 
  end if;
  
  return ret;
end datediff;

-- TEST:
-- Zeit zwischen einem Date und dem Sysdate:
    select dbw.datediff(trunc(sysdate)) test 
    from dual;

-- Zeit zwischen zwei Dates
    select dbw.datediff(trunc(sysdate),sysdate+1/3600) test 
    from dual;
   
-- Zeit zwischen zwei Dates inkl. Formatierung gem. Description im Skript
    select dbw.datediff(sysdate,trunc(sysdate-4),4,'[','h ','m ','s]') test 
    from dual;

/