| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaDjcal ( int ndp, double djm, int iymdf[4], int *j )
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| 4 | /*
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| 5 | ** - - - - - - - - -
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| 6 | ** s l a D j c a l
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| 7 | ** - - - - - - - - -
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| 8 | **
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| 9 | ** Modified Julian Date to Gregorian calendar, expressed
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| 10 | ** in a form convenient for formatting messages (namely
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| 11 | ** rounded to a specified precision, and with the fields
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| 12 | ** stored in a single array).
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| 13 | **
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| 14 | ** Given:
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| 15 | ** ndp int number of decimal places of days in fraction
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| 16 | ** djm double Modified Julian Date (JD-2400000.5)
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| 17 | **
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| 18 | ** Returned:
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| 19 | ** iymdf int[4] year, month, day, fraction in Gregorian calendar
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| 20 | ** *j int status: nonzero = out of range
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| 21 | **
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| 22 | ** Any date after 4701BC March 1 is accepted.
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| 23 | **
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| 24 | ** Large ndp values risk internal overflows. It is typically safe
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| 25 | ** to use up to ndp=4.
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| 26 | **
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| 27 | ** The algorithm is derived from that of Hatcher 1984 (QJRAS 25, 53-55).
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| 28 | **
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| 29 | ** Defined in slamac.h: dmod
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| 30 | **
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| 31 | ** Last revision: 17 August 1999
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| 32 | **
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| 33 | ** Copyright P.T.Wallace. All rights reserved.
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| 34 | */
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| 35 | {
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| 36 | double fd, df, f, d;
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| 37 | long jd, n4, nd10;
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| 38 |
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| 39 | /* Validate */
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| 40 | if ( ( djm <= -2395520.0 ) || ( djm >= 1.0e9 ) ) {
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| 41 | *j = - 1;
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| 42 | return;
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| 43 | } else {
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| 44 |
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| 45 | /* Denominator of fraction */
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| 46 | fd = pow ( 10.0, (double) gmax ( ndp, 0 ) );
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| 47 | fd = dnint ( fd );
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| 48 |
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| 49 | /* Round date and express in units of fraction */
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| 50 | df = djm * fd;
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| 51 | df = dnint ( df );
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| 52 |
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| 53 | /* Separate day and fraction */
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| 54 | f = dmod ( df, fd );
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| 55 | if ( f < 0.0 ) f += fd;
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| 56 | d = ( df - f ) / fd;
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| 57 |
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| 58 | /* Express day in Gregorian calendar */
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| 59 | jd = (long) dnint ( d ) + 2400001L;
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| 60 | n4 = 4L * ( jd + ( ( 2L * ( ( 4L * jd - 17918L ) / 146097L)
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| 61 | * 3L ) / 4L + 1L ) / 2L - 37L );
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| 62 | nd10 = 10L * ( ( ( n4 - 237L ) % 1461L ) / 4L ) + 5L;
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| 63 | iymdf[0] = (int) ( ( n4 / 1461L ) - 4712L );
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| 64 | iymdf[1] = (int) ( ( ( nd10 / 306L + 2L ) % 12L ) + 1L );
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| 65 | iymdf[2] = (int) ( ( nd10 % 306L ) / 10L + 1L );
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| 66 | iymdf[3] = (int) dnint ( f );
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| 67 | *j = 0;
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| 68 | }
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| 69 | }
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