Last change
on this file since 6099cac was 3ae31e9, checked in by Thomas Lopatic <thomas@…>, 8 years ago |
Imported original source code.
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1 | /*
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2 | =============================================================================
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3 | jday.c -- convert date to Julian day. -- ACM algorithm 199
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4 |
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5 | A Julian day is the number of days since some base date
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6 | in the very distant past.
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7 |
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8 | Handy for getting date of x number of days after a given Julian date
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9 | Use jdate() to get that from the Gregorian date.
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10 |
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11 | Written by: Robert G. Tantzen
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12 |
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13 | Translated to C by: Nat Howard
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14 |
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15 | Revised by: D.N. Lynx Crowe
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16 | 1998-01-14 -- optimized for speed
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17 |
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18 | Translated from the algol original in Collected Algorithms of the <ACM
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19 | This and jdate() are algorithm 199.
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20 | =============================================================================
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21 | */
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22 |
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23 | long
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24 | jday(mon, day, year)
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25 | int mon, day, year;
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26 | {
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27 | register long y = year;
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28 | register long m = mon;
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29 | register long j;
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30 | register long ya;
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31 | register long c;
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32 | long d = day;
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33 |
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34 | if(m > 2) {
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35 |
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36 | m -= 3L;
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37 |
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38 | } else {
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39 |
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40 | m += 9L;
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41 | --y;
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42 | }
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43 |
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44 | c = y / 100L;
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45 | ya = y - (100L * c);
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46 |
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47 | j = (146097L * c) / 4L
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48 | + (1461L * ya) / 4L
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49 | + (153L * m + 2L) / 5L
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50 | + d + 1721119L;
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51 |
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52 | return(j);
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53 | }
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