, case TF.UNIT
    when 'D' then (trunc(S.RECKONING_DATE) - trunc(ST.DATE_BEG)) / TF.QTY
    when 'W' then trunc((trunc(S.RECKONING_DATE) - ST.DATE_BEG - decode(TF.ZERO, 0, 0, TF.QTY - 1 + (trunc(ST.DATE_BEG, 'DD') - trunc(ST.DATE_BEG, 'IW'))) + 1) / TF.QTY / 7)
    when 'M' then trunc(months_between(trunc(S.RECKONING_DATE), to_date(to_char(ST.DATE_BEG,'YYYY')||to_char(ST.DATE_BEG,'MM')||to_char(decode(TF.ZERO, 0, extract(day from ST.DATE_BEG), TF.ZERO), 'FM00'), 'YYYYMMDD')) / TF.QTY)
    when 'Y' then trunc(months_between(trunc(S.RECKONING_DATE), to_date(to_char(ST.DATE_BEG,'YYYY')||to_char(decode(TF.ZERO, 0, extract(month from ST.DATE_BEG), TF.ZERO), 'FM00')||to_char(decode(TF.ZERO, 0, extract(day from ST.DATE_BEG), 1), 'FM00'), 'YYYYMMDD'))  / TF.QTY / 12)
    else null
  end                                  as PERIODS

DECLARE

FUNCTION PERIOD_LEN(date1 DATE, date2 DATE, period VARCHAR2 := 'M', len NUMBER := 1) RETURN NUMBER
IS
  d1 DATE;
  d2 DATE;
  l1 NUMBER;
  l2 NUMBER;
BEGIN
  d1 := trunc(least(date1, date2));
  d2 := trunc(greatest(date1, date2));
  IF (d1 = d2) THEN RETURN 0; END IF;
  l1 := extract(day from last_day(d1));
  l2 := extract(day from last_day(d2));
  RETURN months_between(d1, d2);
END;

BEGIN
  open :RECORDSET for
  with t as
  (
    select sysdate d1, sysdate d2 from dual where 0=1
    union all select date '2022-02-28', date '2022-01-27' from dual
    union all select date '2022-02-28', date '2022-01-28' from dual
    union all select date '2022-02-28', date '2022-01-31' from dual
    union all select date '2022-02-28', date '2021-08-31' from dual
    union all select date '2022-02-28', date '2021-08-30' from dual
    union all select date '2022-02-28', date '2021-08-28' from dual
    union all select date '2022-02-27', date '2021-08-31' from dual
    union all select date '2022-02-27', date '2021-08-30' from dual
    union all select date '2022-02-20', date '2021-08-20' from dual
    union all select date '2022-02-15', date '2021-08-17' from dual
  )
  select d1, d2, period_len(d1, d2)
  from t;
END;

   FUNCTION period_days (
      cnt_period_id_arg   IN   bm_cnt_period.cnt_period_id%TYPE,
      date_arg            IN   DATE DEFAULT TRUNC (SYSDATE, 'DD')
   )
      RETURN NUMBER
   IS
      date_var     DATE;
      period_var   bm_cnt_period%ROWTYPE;
   BEGIN
      SELECT *
        INTO period_var
        FROM bm_cnt_period
       WHERE bm_cnt_period.cnt_period_id = cnt_period_id_arg;

      date_var := TRUNC (date_arg, 'DD');
...

  FUNCTION period_count (
             p_date_from IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_date_next IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_period IN BM_CNT_PERIOD.CNT_PERIOD_ID%TYPE
             )
             RETURN NUMBER
  IS
    v_period BM_CNT_PERIOD%ROWTYPE;
  BEGIN
    select * into v_period from BM_CNT_PERIOD where CNT_PERIOD_ID = p_period;
    RETURN period_count(p_date_from, p_date_next, v_period.UNIT, v_period.VALUE, v_period.ADJUST);
  END;
  FUNCTION period_count (
             p_date_from IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_date_next IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_period IN NUMBER
             )
             RETURN NUMBER
  IS
    v_period BM_CNT_PERIOD%ROWTYPE;
  BEGIN
    select * into v_period from BM_CNT_PERIOD where CNT_PERIOD_ID = p_period;
    RETURN period_count(p_date_from, p_date_next, v_period.UNIT, v_period.VALUE, v_period.ADJUST);
  END;
  FUNCTION period_count (
             p_date_from IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_date_next IN DATE DEFAULT TRUNC(SYSDATE, 'DD') ,
             p_period IN VARCHAR2 := 'M' ,
             p_period_value IN NUMBER := 1 ,
             p_period_adjust IN NUMBER := 0
             )
             RETURN NUMBER
  IS
    d1 DATE; d2 DATE;
  BEGIN
    d1 := trunc(least(p_date_from, p_date_next));
    d2 := trunc(greatest(p_date_from, p_date_next));
    IF (p_period = 'D') THEN
      RETURN (d2 - d1) / p_period_value;
    ELSIF (p_period = 'W') THEN
      IF (p_period_adjust > 0) THEN
        d1 := trunc(d1, 'IW') + p_period_adjust - 1;
      END IF;
      RETURN (d2 - d1) / p_period_value / 7;
    ELSIF (p_period = 'M') THEN
      IF (p_period_adjust > 0) THEN
        d1 := trunc(d1, 'MM') + p_period_adjust - 1;
      END IF;
      RETURN months_between(d2+1, d1+1) / p_period_value;
    ELSIF (p_period = 'Y') THEN
      IF (p_period_adjust > 0) THEN
        d1 := add_months(trunc(d1, 'YYYY'), p_period_adjust - 1);
      END IF;
      d2 := trunc(d2, 'MM');
      RETURN months_between(d2, d1) / p_period_value / 12;
    ELSE
      RETURN null;
    END IF;
  END;