| 1 | #include "slalib.h"
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| 2 | #include "slamac.h"
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| 3 | void slaCldj ( int iy, int im, int id, double *djm, int *j )
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| 4 | /*
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| 5 | ** - - - - - - - -
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| 6 | ** s l a C l d j
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| 7 | ** - - - - - - - -
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| 8 | **
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| 9 | ** Gregorian calendar to Modified Julian Date.
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| 10 | **
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| 11 | ** Given:
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| 12 | ** iy,im,id int year, month, day in Gregorian calendar
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| 13 | **
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| 14 | ** Returned:
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| 15 | ** *djm double Modified Julian Date (JD-2400000.5) for 0 hrs
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| 16 | ** *j int status:
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| 17 | ** 0 = OK
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| 18 | ** 1 = bad year (MJD not computed)
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| 19 | ** 2 = bad month (MJD not computed)
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| 20 | ** 3 = bad day (MJD computed)
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| 21 | **
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| 22 | ** The year must be -4699 (i.e. 4700BC) or later.
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| 23 | **
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| 24 | ** The algorithm is derived from that of Hatcher 1984 (QJRAS 25, 53-55).
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| 25 | **
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| 26 | ** Last revision: 29 August 1994
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| 27 | **
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| 28 | ** Copyright P.T.Wallace. All rights reserved.
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| 29 | */
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| 30 | {
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| 31 | long iyL, imL;
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| 32 |
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| 33 | /* Month lengths in days */
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| 34 | static int mtab[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
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| 35 |
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| 36 |
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| 37 |
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| 38 | /* Validate year */
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| 39 | if ( iy < -4699 ) { *j = 1; return; }
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| 40 |
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| 41 | /* Validate month */
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| 42 | if ( ( im < 1 ) || ( im > 12 ) ) { *j = 2; return; }
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| 43 |
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| 44 | /* Allow for leap year */
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| 45 | mtab[1] = ( ( ( iy % 4 ) == 0 ) &&
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| 46 | ( ( ( iy % 100 ) != 0 ) || ( ( iy % 400 ) == 0 ) ) ) ?
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| 47 | 29 : 28;
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| 48 |
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| 49 | /* Validate day */
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| 50 | *j = ( id < 1 || id > mtab[im-1] ) ? 3 : 0;
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| 51 |
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| 52 | /* Lengthen year and month numbers to avoid overflow */
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| 53 | iyL = (long) iy;
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| 54 | imL = (long) im;
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| 55 |
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| 56 | /* Perform the conversion */
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| 57 | *djm = (double)
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| 58 | ( ( 1461L * ( iyL - ( 12L - imL ) / 10L + 4712L ) ) / 4L
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| 59 | + ( 306L * ( ( imL + 9L ) % 12L ) + 5L ) / 10L
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| 60 | - ( 3L * ( ( iyL - ( 12L - imL ) / 10L + 4900L ) / 100L ) ) / 4L
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| 61 | + (long) id - 2399904L );
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| 62 | }
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