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Diffstat (limited to 'src/slalib/djcal.f')
| -rw-r--r-- | src/slalib/djcal.f | 77 |
1 files changed, 77 insertions, 0 deletions
diff --git a/src/slalib/djcal.f b/src/slalib/djcal.f new file mode 100644 index 0000000..7da1a07 --- /dev/null +++ b/src/slalib/djcal.f @@ -0,0 +1,77 @@ + SUBROUTINE sla_DJCAL (NDP, DJM, IYMDF, J) +*+ +* - - - - - - +* D J C A L +* - - - - - - +* +* 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 derived from that of Hatcher 1984 +* (QJRAS 25, 53-55). +* +* P.T.Wallace Starlink 27 April 1998 +* +* Copyright (C) 1998 Rutherford Appleton Laboratory +*- + + 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 |