IOIPSL/Calendar/ymds2ju.f90

module ymds2ju_m

  implicit none

contains

  SUBROUTINE ymds2ju (year, month, day, sec, julian)

    ! Converts year, month, day and seconds into a julian day

    ! In 1968 in a letter to the editor of Communications of the ACM
    ! (CACM, volume 11, number 10, October 1968, p.657) Henry F. Fliegel
    ! and Thomas C. Van Flandern presented such an algorithm.

    ! See also: http://www.magnet.ch/serendipity/hermetic/cal_stud/jdn.htm

    ! In the case of the Gregorian calendar we have chosen to use
    ! the Lilian day numbers. This is the day counter which starts
    ! on the 15th October 1582.
    ! This is the day at which Pope Gregory XIII introduced the
    ! Gregorian calendar.
    ! Compared to the true Julian calendar, which starts some
    ! 7980 years ago, the Lilian days are smaler and are dealt with
    ! easily on 32 bit machines. With the true Julian days you can only
    ! the fraction of the day in the real part to a precision of
    ! a 1/4 of a day with 32 bits.

    USE calendar, ONLY: lock_unan, un_jour
    USE ioconf_calendar_m, ONLY: mon_len, un_an

    INTEGER, INTENT(IN):: year, month, day
    REAL, INTENT(IN):: sec
    REAL, INTENT(OUT):: julian

    ! Local:

    INTEGER:: julian_day
    REAL:: julian_sec
    INTEGER:: jd, m, y, d, ml

    !--------------------------------------------------------------------

    lock_unan = .TRUE.

    m = month
    y = year
    d = day

    ! We deduce the calendar from the length of the year as it
    ! is faster than an INDEX on the calendar variable.

    ! Gregorian
    IF ( (un_an > 365.0).AND.(un_an < 366.0) ) THEN
       jd = (1461*(y+4800+INT(( m-14 )/12)))/4 &
            &      +(367*(m-2-12*(INT(( m-14 )/12))))/12 &
            &      -(3*((y+4900+INT((m-14)/12))/100))/4 &
            &      +d-32075
       jd = jd-2299160
       ! No leap or All leap
    ELSE IF (ABS(un_an-365.0) <= EPSILON(un_an) .OR. &
         &   ABS(un_an-366.0) <= EPSILON(un_an)) THEN
       ml = SUM(mon_len(1:m-1))
       jd = y*INT(un_an)+ml+(d-1)
       ! Calendar with regular month
    ELSE
       ml = INT(un_an)/12
       jd = y*INT(un_an)+(m-1)*ml+(d-1)
    ENDIF

    julian_day = jd
    julian_sec = sec

    julian = julian_day + julian_sec / un_jour

  END SUBROUTINE ymds2ju

end module ymds2ju_m
1	guez	92	module ymds2ju_m
2
3			implicit none
4
5			contains
6
7			SUBROUTINE ymds2ju (year, month, day, sec, julian)
8
9	guez	93	! Converts year, month, day and seconds into a julian day
10	guez	92
11	guez	93	! In 1968 in a letter to the editor of Communications of the ACM
12			! (CACM, volume 11, number 10, October 1968, p.657) Henry F. Fliegel
13			! and Thomas C. Van Flandern presented such an algorithm.
14
15			! See also: http://www.magnet.ch/serendipity/hermetic/cal_stud/jdn.htm
16
17			! In the case of the Gregorian calendar we have chosen to use
18			! the Lilian day numbers. This is the day counter which starts
19			! on the 15th October 1582.
20			! This is the day at which Pope Gregory XIII introduced the
21			! Gregorian calendar.
22			! Compared to the true Julian calendar, which starts some
23			! 7980 years ago, the Lilian days are smaler and are dealt with
24			! easily on 32 bit machines. With the true Julian days you can only
25			! the fraction of the day in the real part to a precision of
26			! a 1/4 of a day with 32 bits.
27
28			USE calendar, ONLY: lock_unan, un_jour
29			USE ioconf_calendar_m, ONLY: mon_len, un_an
30
31	guez	92	INTEGER, INTENT(IN):: year, month, day
32			REAL, INTENT(IN):: sec
33			REAL, INTENT(OUT):: julian
34
35	guez	93	! Local:
36
37	guez	92	INTEGER:: julian_day
38			REAL:: julian_sec
39	guez	93	INTEGER:: jd, m, y, d, ml
40	guez	92
41			!--------------------------------------------------------------------
42
43	guez	93	lock_unan = .TRUE.
44
45			m = month
46			y = year
47			d = day
48
49			! We deduce the calendar from the length of the year as it
50			! is faster than an INDEX on the calendar variable.
51
52			! Gregorian
53			IF ( (un_an > 365.0).AND.(un_an < 366.0) ) THEN
54			jd = (1461*(y+4800+INT(( m-14 )/12)))/4 &
55			& +(367(m-2-12(INT(( m-14 )/12))))/12 &
56			& -(3*((y+4900+INT((m-14)/12))/100))/4 &
57			& +d-32075
58			jd = jd-2299160
59			! No leap or All leap
60			ELSE IF (ABS(un_an-365.0) <= EPSILON(un_an) .OR. &
61			& ABS(un_an-366.0) <= EPSILON(un_an)) THEN
62			ml = SUM(mon_len(1:m-1))
63			jd = y*INT(un_an)+ml+(d-1)
64			! Calendar with regular month
65			ELSE
66			ml = INT(un_an)/12
67			jd = yINT(un_an)+(m-1)ml+(d-1)
68			ENDIF
69
70			julian_day = jd
71			julian_sec = sec
72
73	guez	92	julian = julian_day + julian_sec / un_jour
74
75			END SUBROUTINE ymds2ju
76
77			end module ymds2ju_m