source: trunk/MagicSoft/slalib/djcl.c@ 10083

Last change on this file since 10083 was 731, checked in by tbretz, 24 years ago
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1#include "slalib.h"
2#include "slamac.h"
3void slaDjcl ( double djm, int *iy, int *im, int *id, double *fd, int *j)
4/*
5** - - - - - - - -
6** s l a D j c l
7** - - - - - - - -
8**
9** Modified Julian Date to Gregorian year, month, day,
10** and fraction of a day.
11**
12** Given:
13** djm double Modified Julian Date (JD-2400000.5)
14**
15** Returned:
16** *iy int year
17** *im int month
18** *id int day
19** *fd double fraction of day
20** *j int status:
21** -1 = unacceptable date (before 4701BC March 1)
22**
23** The algorithm is derived from that of Hatcher 1984 (QJRAS 25, 53-55).
24**
25** Defined in slamac.h: dmod
26**
27** Last revision: 12 March 1998
28**
29** Copyright P.T.Wallace. All rights reserved.
30*/
31{
32 double f, d;
33 long jd, n4, nd10;
34
35/* Check if date is acceptable */
36 if ( ( djm <= -2395520.0 ) || ( djm >= 1e9 ) ) {
37 *j = -1;
38 return;
39 } else {
40 *j = 0;
41
42 /* Separate day and fraction */
43 f = dmod ( djm, 1.0 );
44 if ( f < 0.0 ) f += 1.0;
45 d = djm - f;
46 d = dnint ( d );
47
48 /* Express day in Gregorian calendar */
49 jd = (long) dnint ( d ) + 2400001;
50 n4 = 4L*(jd+((6L*((4L*jd-17918L)/146097L))/4L+1L)/2L-37L);
51 nd10 = 10L*(((n4-237L)%1461L)/4L)+5L;
52 *iy = (int) (n4/1461L-4712L);
53 *im = (int) (((nd10/306L+2L)%12L)+1L);
54 *id = (int) ((nd10%306L)/10L+1L);
55 *fd = f;
56 *j = 0;
57 }
58}
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