| 1 | #include "slalib.h"
|
|---|
| 2 | #include "slamac.h"
|
|---|
| 3 | void slaClyd ( int iy, int im, int id, int *ny, int *nd, int *jstat )
|
|---|
| 4 | /*
|
|---|
| 5 | ** - - - - - - - -
|
|---|
| 6 | ** s l a C l y d
|
|---|
| 7 | ** - - - - - - - -
|
|---|
| 8 | **
|
|---|
| 9 | ** Gregorian calendar to year and day in year (in a Julian calendar
|
|---|
| 10 | ** aligned to the 20th/21st century Gregorian calendar).
|
|---|
| 11 | **
|
|---|
| 12 | ** Given:
|
|---|
| 13 | ** iy,im,id int year, month, day in Gregorian calendar
|
|---|
| 14 | **
|
|---|
| 15 | ** Returned:
|
|---|
| 16 | ** ny int year (re-aligned Julian calendar)
|
|---|
| 17 | ** nd int day in year (1 = January 1st)
|
|---|
| 18 | ** jstat int status:
|
|---|
| 19 | ** 0 = OK
|
|---|
| 20 | ** 1 = bad year (before -4711)
|
|---|
| 21 | ** 2 = bad month
|
|---|
| 22 | ** 3 = bad day (but conversion performed)
|
|---|
| 23 | **
|
|---|
| 24 | ** Notes:
|
|---|
| 25 | **
|
|---|
| 26 | ** 1 This routine exists to support the low-precision routines
|
|---|
| 27 | ** slaEarth, slaMoon and slaEcor.
|
|---|
| 28 | **
|
|---|
| 29 | ** 2 Between 1900 March 1 and 2100 February 28 it returns answers
|
|---|
| 30 | ** which are consistent with the ordinary Gregorian calendar.
|
|---|
| 31 | ** Outside this range there will be a discrepancy which increases
|
|---|
| 32 | ** by one day for every non-leap century year.
|
|---|
| 33 | **
|
|---|
| 34 | ** 3 The essence of the algorithm is first to express the Gregorian
|
|---|
| 35 | ** date as a Julian Day Number and then to convert this back to
|
|---|
| 36 | ** a Julian calendar date, with day-in-year instead of month and
|
|---|
| 37 | ** day. See 12.92-1 and 12.95-1 in the reference.
|
|---|
| 38 | **
|
|---|
| 39 | ** Reference: Explanatory Supplement to the Astronomical Almanac,
|
|---|
| 40 | ** ed P.K.Seidelmann, University Science Books (1992),
|
|---|
| 41 | ** p604-606.
|
|---|
| 42 | **
|
|---|
| 43 | ** Last revision: 26 November 1994
|
|---|
| 44 | **
|
|---|
| 45 | ** Copyright P.T.Wallace. All rights reserved.
|
|---|
| 46 | */
|
|---|
| 47 | {
|
|---|
| 48 | long i, j, k, l, n, iyL, imL;
|
|---|
| 49 |
|
|---|
| 50 | /* Month lengths in days */
|
|---|
| 51 | static int mtab[12] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
|
|---|
| 52 |
|
|---|
| 53 |
|
|---|
| 54 |
|
|---|
| 55 | /* Validate year */
|
|---|
| 56 | if ( iy < -4711 ) { *jstat = 1; return; }
|
|---|
| 57 |
|
|---|
| 58 | /* Validate month */
|
|---|
| 59 | if ( ( im < 1 ) || ( im > 12 ) ) { *jstat = 2; return; }
|
|---|
| 60 |
|
|---|
| 61 | /* Allow for (Gregorian) leap year */
|
|---|
| 62 | mtab[1] = ( ( ( iy % 4 ) == 0 ) &&
|
|---|
| 63 | ( ( ( iy % 100 ) != 0 ) || ( ( iy % 400 ) == 0 ) ) ) ?
|
|---|
| 64 | 29 : 28;
|
|---|
| 65 |
|
|---|
| 66 | /* Validate day */
|
|---|
| 67 | *jstat = ( id < 1 || id > mtab[im-1] ) ? 3 : 0;
|
|---|
| 68 |
|
|---|
| 69 | /* Perform the conversion */
|
|---|
| 70 | iyL = (long) iy;
|
|---|
| 71 | imL = (long) im;
|
|---|
| 72 | i = ( 14 - imL ) /12L;
|
|---|
| 73 | k = iyL - i;
|
|---|
| 74 | j = ( 1461L * ( k + 4800L ) ) / 4L
|
|---|
| 75 | + ( 367L * ( imL - 2L + 12L * i ) ) / 12L
|
|---|
| 76 | - ( 3L * ( ( k + 4900L ) / 100L ) ) / 4L + (long) id - 30660L;
|
|---|
| 77 | k = ( j - 1L ) / 1461L;
|
|---|
| 78 | l = j - 1461L * k;
|
|---|
| 79 | n = ( l - 1L ) / 365L - l / 1461L;
|
|---|
| 80 | j = ( ( 80L * ( l - 365L * n + 30L ) ) / 2447L ) / 11L;
|
|---|
| 81 | i = n + j;
|
|---|
| 82 | *nd = 59 + (int) ( l -365L * i + ( ( 4L - n ) / 4L ) * ( 1L - j ) );
|
|---|
| 83 | *ny = (int) ( 4L * k + i ) - 4716;
|
|---|
| 84 | }
|
|---|
