1 files changed, 93 insertions, 0 deletions
diff --git a/math/slalib/djcal.f b/math/slalib/djcal.f
new file mode 100644
index 00000000..31766d18
--- /dev/null
+++ b/math/slalib/djcal.f
@@ -0,0 +1,93 @@
+      SUBROUTINE slDJCA (NDP, DJM, IYMDF, J)
+*+
+*     - - - - - -
+*      D J C A
+*     - - - - - -
+*
+*  Modified Julian Date to Gregorian Calendar, expressed
+*  in a form convenient for formatting messages (namely
+*  rounded to a specified precision, and with the fields
+*  stored in a single array)
+*
+*  Given:
+*     NDP      i      number of decimal places of days in fraction
+*     DJM      d      modified Julian Date (JD-2400000.5)
+*
+*  Returned:
+*     IYMDF    i(4)   year, month, day, fraction in Gregorian
+*                     calendar
+*     J        i      status:  nonzero = out of range
+*
+*  Any date after 4701BC March 1 is accepted.
+*
+*  NDP should be 4 or less if internal overflows are to be avoided
+*  on machines which use 32-bit integers.
+*
+*  The algorithm is adapted from Hatcher 1984 (QJRAS 25, 53-55).
+*
+*  Last revision:   22 July 2004
+*
+*  Copyright P.T.Wallace.  All rights reserved.
+*
+*  License:
+*    This program is free software; you can redistribute it and/or modify
+*    it under the terms of the GNU General Public License as published by
+*    the Free Software Foundation; either version 2 of the License, or
+*    (at your option) any later version.
+*
+*    This program is distributed in the hope that it will be useful,
+*    but WITHOUT ANY WARRANTY; without even the implied warranty of
+*    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+*    GNU General Public License for more details.
+*
+*    You should have received a copy of the GNU General Public License
+*    along with this program (see SLA_CONDITIONS); if not, write to the
+*    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+*    Boston, MA  02110-1301  USA
+*
+*  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+*-
+
+      IMPLICIT NONE
+
+      INTEGER NDP
+      DOUBLE PRECISION DJM
+      INTEGER IYMDF(4),J
+
+      INTEGER NFD
+      DOUBLE PRECISION FD,DF,F,D
+      INTEGER JD,N4,ND10
+
+
+*  Validate.
+      IF ( DJM.LE.-2395520D0 .OR. DJM.GE.1D9 ) THEN
+         J = -1
+      ELSE
+         J = 0
+
+*     Denominator of fraction.
+         NFD = 10**MAX(NDP,0)
+         FD = DBLE(NFD)
+
+*     Round date and express in units of fraction.
+         DF = ANINT(DJM*FD)
+
+*     Separate day and fraction.
+         F = MOD(DF,FD)
+         IF (F.LT.0D0) F = F+FD
+         D = (DF-F)/FD
+
+*     Express day in Gregorian calendar.
+         JD = NINT(D)+2400001
+
+         N4 = 4*(JD+((2*((4*JD-17918)/146097)*3)/4+1)/2-37)
+         ND10 = 10*(MOD(N4-237,1461)/4)+5
+
+         IYMDF(1) = N4/1461-4712
+         IYMDF(2) = MOD(ND10/306+2,12)+1
+         IYMDF(3) = MOD(ND10,306)/10+1
+         IYMDF(4) = NINT(F)
+
+      END IF
+
+      END