65 lines
1.8 KiB
Go
65 lines
1.8 KiB
Go
/*
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Copyright 2017 SAP SE
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Licensed under the Apache License, Version 2.0 (the "License");
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you may not use this file except in compliance with the License.
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You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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*/
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package protocol
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import (
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"time"
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)
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const gregorianDay = 2299161 // Start date of Gregorian Calendar as Julian Day Number
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var gregorianDate = julianDayToTime(gregorianDay) // Start date of Gregorian Calendar (1582-10-15)
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// timeToJulianDay returns the Julian Date Number of time's date components.
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// The algorithm is taken from https://en.wikipedia.org/wiki/Julian_day.
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func timeToJulianDay(t time.Time) int {
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t = t.UTC()
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month := int(t.Month())
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a := (14 - month) / 12
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y := t.Year() + 4800 - a
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m := month + (12 * a) - 3
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if t.Before(gregorianDate) { // Julian Calendar
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return t.Day() + (153*m+2)/5 + 365*y + y/4 - 32083
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}
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// Gregorian Calendar
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return t.Day() + (153*m+2)/5 + 365*y + y/4 - y/100 + y/400 - 32045
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}
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// JulianDayToTime returns the correcponding UTC date for a Julian Day Number.
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// The algorithm is taken from https://en.wikipedia.org/wiki/Julian_day.
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func julianDayToTime(jd int) time.Time {
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var f int
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if jd < gregorianDay {
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f = jd + 1401
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} else {
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f = jd + 1401 + (((4*jd+274277)/146097)*3)/4 - 38
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}
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e := 4*f + 3
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g := (e % 1461) / 4
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h := 5*g + 2
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day := (h%153)/5 + 1
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month := (h/153+2)%12 + 1
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year := (e / 1461) - 4716 + (12+2-month)/12
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return time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC)
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}
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