SUBROUTINE TSDATE(DATE,YEAR,PERIOD,FREQ)
      IMPLICIT INTEGER (A-Z)
C
C          THIS SUBROUTINE MAKES A TSP DATE FROM THE YEAR,
C     PERIOD, AND FREQUENCY FREQ.
C          YEARS CAN EITHER BE 2 DIGIT OR 4 DIGIT; ANY YEAR LESS THAN
C     200 IS ASSUMED TO BE A 2 DIGIT YEAR.  THIS MEANS ONE CAN GO UP
C     TO 2099 WITH 2 DIGIT YEARS.  OF COURSE, IN THIS CASE, THE YEAR
C     WILL ACTUALLY BE 3 DIGITS.
C              BRONWYN H. HALL   APRIL 1982
C     4.3  OPTIONS BASEYEAR=1900/2000/0  USER CONTROLS BASE YEAR,
C     WHICH ALLOWS FOR YEARS NEAR 0, OR YEARS CENTERED AROUND 2000.
C
      COMMON /COM43/ NOT43(5),IYBASE
      DIMENSION WARN1(16)
C      DATA IYBASE/1900/
      DATA CUTOFF/200/
      DATA WARN1/4HPeri,4Hod s,4Hpeci,4Hfied,4H too,4H big,4H for,
     *           4H fre,4Hquen,4Hcy; ,4Hit i,4Hs be,4Hing ,4Hset ,
     *           4Hto 1,4H.   /
C
C          CHECK FOR UNDATED SERIES.
C
      IF (FREQ.GT.0) GO TO 5
      DATE = YEAR
      IF (PERIOD.LE.1) RETURN
      CALL WRNPRT(16,WARN1,PERIOD,6)
      PERIOD = 1
      RETURN
C
C          DATED SERIES.
C
    5 IF (YEAR.LE.CUTOFF .AND. YEAR.GE.0) YEAR = YEAR+IYBASE
      PER = PERIOD
      IF (PER.LE.FREQ) GO TO 10
C
C           ILLEGAL PERIOD - PRINT WARNING AND CONTINUE.
C
      CALL WRNPRT(16,WARN1,PER,6)
      PER = 1
   10 DATE = YEAR*FREQ+PER-1
      RETURN
C
      ENTRY UNTSDT(DATE,YEAR,PERIOD,FREQ)
C
C          CHECK FOR UNDATED SERIES.
C
      IF (FREQ.GT.0) GO TO 15
      YEAR = DATE
      PERIOD = 1
      RETURN
C
C           DATED SERIES
C
   15 YEAR = DATE/FREQ
      PERIOD = DATE-YEAR*FREQ+1
      IF (YEAR.LE.CUTOFF .AND. YEAR.GE.0) YEAR = YEAR+IYBASE
      RETURN
      END