46 lines
1.1 KiB
C
46 lines
1.1 KiB
C
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#include "tai.h"
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#include "caldate.h"
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void caldate_frommjd(struct caldate *cd, int64_t day, int *pwday, int *pyday)
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{
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long year;
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long month;
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int yday;
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year = (long)(day / LL(146097));
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day %= LL(146097);
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day += LL(678881);
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while (day >= LL(146097)) { day -= LL(146097); ++year; }
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/* year * 146097 + day - 678881 is MJD; 0 <= day < 146097 */
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/* 2000-03-01, MJD 51604, is year 5, day 0 */
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if (pwday) *pwday = (int)((day + 3) % 7);
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year *= 4;
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if (day == LL(146096)) { year += 3; day = 36524L; }
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else { year += (long)(day / LL(36524)); day %= LL(36524); }
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year *= 25;
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year += (long)(day / 1461);
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day %= 1461;
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year *= 4;
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yday = (day < 306);
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if (day == 1460) { year += 3; day = 365; }
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else { year += (long)(day / 365); day %= 365; }
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yday += (long)day;
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day *= 10;
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month = (long)((day + 5) / 306);
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day = (day + 5) % 306;
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day /= 10;
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if (month >= 10) { yday -= 306; ++year; month -= 10; }
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else { yday += 59; month += 2; }
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cd->year = year;
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cd->month = month + 1;
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cd->day = (long)(day + 1);
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if (pyday) *pyday = yday;
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}
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