SUBROUTINE iau_JD2CAL ( DJ1, DJ2, IY, IM, ID, FD, J ) *+ * - - - - - - - - - - - * i a u _ J D 2 C A L * - - - - - - - - - - - * * Julian Date to Gregorian year, month, day, and fraction of a day. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * DJ1,DJ2 d Julian Date (Notes 1, 2) * * Returned: * IY i year * IM i month * ID i day * FD d fraction of day * J i status: * 0 = OK * -1 = unacceptable date (Note 1) * * Notes: * * 1) The earliest valid date is -68569.5 (-4900 March 1). The * largest value accepted is 10^9. * * 2) The Julian Date is apportioned in any convenient way between * the arguments DJ1 and DJ2. For example, JD=2450123.7 could * be expressed in any of these ways, among others: * * DJ1 DJ2 * * 2450123.7D0 0D0 (JD method) * 2451545D0 -1421.3D0 (J2000 method) * 2400000.5D0 50123.2D0 (MJD method) * 2450123.5D0 0.2D0 (date & time method) * * Separating integer and fraction uses the "compensated summation" * algorithm of Kahan-Neumaier to preserve as much precision as * possible irrespective of the JD1+JD2 apportionment. * * 3) In early eras the conversion is from the "Proleptic Gregorian * Calendar"; no account is taken of the date(s) of adoption of * the Gregorian Calendar, nor is the AD/BC numbering convention * observed. * * References: * * Explanatory Supplement to the Astronomical Almanac, * P. Kenneth Seidelmann (ed), University Science Books (1992), * Section 12.92 (p604). * * Klein, A., A Generalized Kahan-Babuska-Summation-Algorithm. * Computing, 76, 279-293 (2006), Section 3. * * This revision: 2020 October 21 * * SOFA release 2021-05-12 * * Copyright (C) 2021 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DJ1, DJ2 INTEGER IY, IM, ID DOUBLE PRECISION FD INTEGER J * Smallest number such that 1D0+EPS .NE. 1D0 DOUBLE PRECISION EPS PARAMETER ( EPS = 2.2204460492503131D-16 ) * Minimum and maximum allowed JD DOUBLE PRECISION DJMIN, DJMAX PARAMETER ( DJMIN = -68569.5D0, DJMAX = 1D9 ) INTEGER JD, I, L, N, K DOUBLE PRECISION DJ, F1, F2, D, S, CS, V(2), X, T, C, F * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Verify date is acceptable. DJ = DJ1 + DJ2 IF ( DJ.LT.DJMIN .OR. DJ.GT.DJMAX ) THEN J = -1 ELSE J = 0 * Separate day and fraction (where -0.5 <= fraction < 0.5). D = ANINT(DJ1) F1 = DJ1 - D JD = INT(D) D = ANINT(DJ2) F2 = DJ2 - D JD = JD + INT(D) * Compute F1+F2+0.5 using compensated summation (Klein 2006). S = 0.5D0 CS = 0D0 V(1) = F1 V(2) = F2 DO 1 I=1,2 X = V(I) T = S + X IF ( ABS(S) .GE. ABS(X) ) THEN C = (S-T) + X ELSE C = (X-T) + S END IF CS = CS + C S = T IF ( S .GE. 1D0 ) THEN JD = JD + 1 S = S - 1D0 END IF 1 CONTINUE F = S + CS CS = F - S * Deal with negative F. IF ( F .LT. 0D0 ) THEN * Compensated summation: assume that |S| <= 1. F = S + 1D0 CS = CS + ((1D0-F) + S) S = F F = S + CS CS = F - S JD = JD - 1 END IF * Deal with F that is 1D0 or more (when rounded to double). IF ( (F-1D0) .GE. -EPS/4D0 ) THEN * Compensated summation: assume that |S| <= 1. */ T = S - 1D0 CS = CS + ((S-T) - 1D0) S = T F = S + CS IF ( -EPS/2D0 .LT. F ) THEN JD = JD + 1 F = MAX ( F, 0D0 ) END IF END IF * Express day in Gregorian calendar. L = JD + 68569 N = ( 4*L ) / 146097 L = L - ( 146097*N + 3 ) / 4 I = ( 4000 * (L+1) ) / 1461001 L = L - ( 1461*I ) / 4 + 31 K = ( 80*L ) / 2447 ID = L - ( 2447*K ) / 80 L = K / 11 IM = K + 2 - 12*L IY = 100 * ( N-49 ) + I + L FD = F END IF * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2021 * Standards Of Fundamental Astronomy Board * of the International Astronomical Union. * * ===================== * SOFA Software License * ===================== * * NOTICE TO USER: * * BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND * CONDITIONS WHICH APPLY TO ITS USE. * * 1. The Software is owned by the IAU SOFA Board ("SOFA"). * * 2. Permission is granted to anyone to use the SOFA software for any * purpose, including commercial applications, free of charge and * without payment of royalties, subject to the conditions and * restrictions listed below. * * 3. You (the user) may copy and distribute SOFA source code to others, * and use and adapt its code and algorithms in your own software, * on a world-wide, royalty-free basis. That portion of your * distribution that does not consist of intact and unchanged copies * of SOFA source code files is a "derived work" that must comply * with the following requirements: * * a) Your work shall be marked or carry a statement that it * (i) uses routines and computations derived by you from * software provided by SOFA under license to you; and * (ii) does not itself constitute software provided by and/or * endorsed by SOFA. * * b) The source code of your derived work must contain descriptions * of how the derived work is based upon, contains and/or differs * from the original SOFA software. * * c) The names of all routines in your derived work shall not * include the prefix "iau" or "sofa" or trivial modifications * thereof such as changes of case. * * d) The origin of the SOFA components of your derived work must * not be misrepresented; you must not claim that you wrote the * original software, nor file a patent application for SOFA * software or algorithms embedded in the SOFA software. * * e) These requirements must be reproduced intact in any source * distribution and shall apply to anyone to whom you have * granted a further right to modify the source code of your * derived work. * * Note that, as originally distributed, the SOFA software is * intended to be a definitive implementation of the IAU standards, * and consequently third-party modifications are discouraged. All * variations, no matter how minor, must be explicitly marked as * such, as explained above. * * 4. You shall not cause the SOFA software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or * by inappropriate modification. * * 5. The SOFA software is provided "as is" and SOFA makes no warranty * as to its use or performance. SOFA does not and cannot warrant * the performance or results which the user may obtain by using the * SOFA software. SOFA makes no warranties, express or implied, as * to non-infringement of third party rights, merchantability, or * fitness for any particular purpose. In no event will SOFA be * liable to the user for any consequential, incidental, or special * damages, including any lost profits or lost savings, even if a * SOFA representative has been advised of such damages, or for any * claim by any third party. * * 6. The provision of any version of the SOFA software under the terms * and conditions specified herein does not imply that future * versions will also be made available under the same terms and * conditions. * * In any published work or commercial product which uses the SOFA * software directly, acknowledgement (see www.iausofa.org) is * appreciated. * * Correspondence concerning SOFA software should be addressed as * follows: * * By email: sofa@ukho.gov.uk * By post: IAU SOFA Center * HM Nautical Almanac Office * UK Hydrographic Office * Admiralty Way, Taunton * Somerset, TA1 2DN * United Kingdom * *----------------------------------------------------------------------- END