i4dy.f

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C> @file
C> @brief Convert a date-time with a 2-digit year to a date-time with
C> a 4-digit year

C> This function converts a date-time with a 2-digit year (YYMMDDHH)
C> to a date-time with a 4-digit year (YYYYMMDDHH) using a windowing
C> technique.
C>
C> All 2-digit years greater than 40 are assumed to have a 4-digit
C> year beginning with 19 (i.e. 1941-1999), and all 2-digit years less
C> than or equal to 40 are assumed to have a 4-digit year beginning
C> with 20 (i.e. 2000-2040).  If the input date-time already contains
C> a 4-digit year, then the function simply returns that value.
C>
C> @author J. Woollen
C> @date 1998-07-08
C>
C> @param[in] IDATE -- integer: Date-time in format of either YYMMDDHH
C>                     (2-digit year) or YYYYMMDDHH (4-digit year)
C> @returns i4dy -- integer: Date-time in format of YYYYMMDDHH (4-digit
C>                  year)
C>
C> <b>Program History Log:</b>
C> | Date | Programmer | Comments |
C> | -----|------------|----------|
C> | 1998-07-08 | J. Woollen | Original author |
C> | 1998-12-14 | J. Woollen | Modified to use 20 as the 2-digit year for windowing to a 4-digit year (00-20 ==> add 2000; 21-99 ==> add 1900) |
C> | 2003-11-04 | D. Keyser | Modified date calculations to stop using floating point arithmetic since this can lead to round off error and an improper result on some machines |
C> | 2018-06-29 | J. Ator | Changed 2-digit->4-digit year window range to (00-40 ==> add 2000; 41-99 ==> add 1900) |
C>
      FUNCTION i4dy(IDATE)

      IF(idate.LT.10**8) THEN
         iy = idate/10**6
         IF(iy.GT.40) THEN
            i4dy = idate + 19*100000000
         ELSE
            i4dy = idate + 20*100000000
         ENDIF
      ELSE
         i4dy = idate
      ENDIF

      RETURN
      END