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95 lines
2.5 KiB
Fortran
95 lines
2.5 KiB
Fortran
SUBROUTINE sla_CLDJ (IY, IM, ID, DJM, J)
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*+
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* - - - - -
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* C L D J
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* - - - - -
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*
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* Gregorian Calendar to Modified Julian Date
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*
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* Given:
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* IY,IM,ID int year, month, day in Gregorian calendar
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*
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* Returned:
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* DJM dp modified Julian Date (JD-2400000.5) for 0 hrs
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* J int status:
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* 0 = OK
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* 1 = bad year (MJD not computed)
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* 2 = bad month (MJD not computed)
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* 3 = bad day (MJD computed)
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*
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* The year must be -4699 (i.e. 4700BC) or later.
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*
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* The algorithm is adapted from Hatcher 1984 (QJRAS 25, 53-55).
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*
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* Last revision: 27 July 2004
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*
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* Copyright P.T.Wallace. All rights reserved.
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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INTEGER IY,IM,ID
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DOUBLE PRECISION DJM
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INTEGER J
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* Month lengths in days
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INTEGER MTAB(12)
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DATA MTAB / 31,28,31,30,31,30,31,31,30,31,30,31 /
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* Preset status.
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J = 0
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* Validate year.
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IF ( IY .LT. -4699 ) THEN
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J = 1
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ELSE
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* Validate month.
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IF ( IM.GE.1 .AND. IM.LE.12 ) THEN
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* Allow for leap year.
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IF ( MOD(IY,4) .EQ. 0 ) THEN
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MTAB(2) = 29
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ELSE
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MTAB(2) = 28
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END IF
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IF ( MOD(IY,100).EQ.0 .AND. MOD(IY,400).NE.0 )
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: MTAB(2) = 28
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* Validate day.
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IF ( ID.LT.1 .OR. ID.GT.MTAB(IM) ) J=3
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* Modified Julian Date.
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DJM = DBLE ( ( 1461 * ( IY - (12-IM)/10 + 4712 ) ) / 4
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: + ( 306 * MOD ( IM+9, 12 ) + 5 ) / 10
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: - ( 3 * ( ( IY - (12-IM)/10 + 4900 ) / 100 ) ) / 4
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: + ID - 2399904 )
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* Bad month.
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ELSE
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J=2
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END IF
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END IF
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END
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