JGDate Subroutine

private subroutine JGDate(jflag, jdate, gyyyy, gmm, gdd)

Arguments

Type		Name
integer	::	jflag
integer	::	jdate
integer	::	gyyyy
integer	::	gmm
integer	::	gdd
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Source Code

JGDate
Source Code

SUBROUTINE JGDate(jflag,jdate,gyyyy,gmm,gdd)
          ! SUBROUTINE INFORMATION:
          !       AUTHOR         <author>
          !       DATE WRITTEN   <date_written>
          !       MODIFIED       na
          !       RE-ENGINEERED  na

          ! PURPOSE OF THIS SUBROUTINE:
          ! Subroutine JGDate is a gregorian date to actual julian date
          ! converter.  the advantage of storing a julian date in the
          ! jdate format rather than a 5 digit format is that any
          ! number of days can be add or subtracted to jdate and
          ! that result is a proper julian date.

          ! METHODOLOGY EMPLOYED:
          ! <description>

          ! REFERENCES:
          ! for discussion of this algorithm,
          ! see cacm, vol 11, no 10, oct 1968, page 657

          ! USE STATEMENTS:
          ! na

  IMPLICIT NONE ! Enforce explicit typing of all variables in this routine

          ! SUBROUTINE ARGUMENT DEFINITIONS:
  INTEGER :: jflag   ! indicates direction of conversion,
                     ! 1 --> gregorian (dd/mm/yyyy) to julian
                     ! 2 --> julian to gregorian.

  INTEGER :: jdate   ! input/output julian date, typically a 7 or 8 digit integer
  INTEGER :: gyyyy   ! input/output gregorian year, should be specified as 4 digits
  INTEGER :: gmm     ! input/output gregorian month
  INTEGER :: gdd     ! input/output gregorian day

          ! SUBROUTINE PARAMETER DEFINITIONS:
          ! na

          ! INTERFACE BLOCK SPECIFICATIONS:
          ! na

          ! DERIVED TYPE DEFINITIONS:
          ! na

          ! SUBROUTINE LOCAL VARIABLE DECLARATIONS:
  INTEGER :: tdate   ! integer*4 variable needed for double precision arithmetic
  INTEGER :: tyyyy   ! integer*4 variable needed for double precision arithmetic
  INTEGER :: tmm     ! integer*4 variable needed for double precision arithmetic
  INTEGER :: tdd     ! integer*4 variable needed for double precision arithmetic
  INTEGER :: l       ! temporary variable used in conversion.
  INTEGER :: n       ! temporary variable used in conversion.

!
!                                       gregorian to julian
!
      if (jflag == 1) then
        tyyyy=gyyyy
        tmm=gmm
        tdd=gdd
        l= (tmm - 14) / 12
        jdate = tdd - 32075 + 1461 * (tyyyy + 4800 + l)/4 + 367 * (tmm - 2 - l*12)/12 - 3 * ((tyyyy + 4900 + l)/100)/4

      elseif (jflag == 2) then
!
!                                       julian to gregorian
!
        tdate = jdate
        l = tdate + 68569
        n = 4*l / 146097
        l = l - (146097*n + 3) / 4
        tyyyy = 4000*(l+1) / 1461001
        l = l- 1461*tyyyy / 4 + 31
        tmm = 80*l / 2447
        tdd = l - 2447*tmm / 80
        l = tmm/11
        tmm = tmm + 2 - 12*l
        tyyyy = 100 * (n - 49) + tyyyy + l
!c
        gyyyy = tyyyy
        gdd   = tdd
        gmm   = tmm

      endif
!c
      return

END SUBROUTINE JGDate
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