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fix: TimeFromExcelTime #795

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fix: TimeFromExcelTime #795

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20 changes: 13 additions & 7 deletions date.go
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ const (

secondsInADay = float64((24 * time.Hour) / time.Second)
nanosInADay = float64((24 * time.Hour) / time.Nanosecond)
roundEpsilon = 1e-9
)

var (
Expand Down Expand Up @@ -103,28 +104,33 @@ func doTheFliegelAndVanFlandernAlgorithm(jd int) (day, month, year int) {
// Convert an excelTime representation (stored as a floating point number) to a time.Time.
func TimeFromExcelTime(excelTime float64, date1904 bool) time.Time {
var date time.Time
var wholeDaysPart = int(excelTime)
// Excel uses Julian dates prior to March 1st 1900, and
// Gregorian thereafter.
wholeDaysPart := int(excelTime)
// Excel uses Julian dates prior to March 1st 1900, and Gregorian
// thereafter.
if wholeDaysPart <= 61 {
const OFFSET1900 = 15018.0
const OFFSET1904 = 16480.0
const MJD0 float64 = 2400000.5
var date time.Time
if date1904 {
date = julianDateToGregorianTime(MJD_0, excelTime+OFFSET1904)
date = julianDateToGregorianTime(MJD0, excelTime+OFFSET1904)
} else {
date = julianDateToGregorianTime(MJD_0, excelTime+OFFSET1900)
date = julianDateToGregorianTime(MJD0, excelTime+OFFSET1900)
}
return date
}
var floatPart = excelTime - float64(wholeDaysPart)
floatPart := excelTime - float64(wholeDaysPart) + roundEpsilon
if date1904 {
date = excel1904Epoc
} else {
date = excel1900Epoc
}
durationPart := time.Duration(nanosInADay * floatPart)
return date.AddDate(0, 0, wholeDaysPart).Add(durationPart)
date = date.AddDate(0, 0, wholeDaysPart).Add(durationPart)
if date.Nanosecond()/1e6 > 500 {
return date.Round(time.Second)
}
return date.Truncate(time.Second)
}

// TimeToExcelTime will convert a time.Time into Excel's float representation, in either 1900 or 1904
Expand Down
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