33 lines
792 B
Go
33 lines
792 B
Go
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package isoweek
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import "time"
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// DateToJulian converts a date to a Julian day number.
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func DateToJulian(year int, month time.Month, day int) (jdn int) {
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// Claus Tøndering's Calendar FAQ
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// http://www.tondering.dk/claus/cal/julperiod.php#formula
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if month < 3 {
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year = year - 1
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month = month + 12
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}
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year = year + 4800
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return day + (153*(int(month)-3)+2)/5 + 365*year +
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year/4 - year/100 + year/400 - 32045
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}
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// JulianToDate converts a Julian day number to a date.
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func JulianToDate(jdn int) (year int, month time.Month, day int) {
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// Richards, E. G. (2013) pp. 585–624
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e := 4*(jdn+1401+(4*jdn+274277)/146097*3/4-38) + 3
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h := e%1461/4*5 + 2
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day = h%153/5 + 1
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month = time.Month((h/153+2)%12 + 1)
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year = e/1461 - 4716 + (14-int(month))/12
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return year, month, day
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}
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