timeexpression/util.go at master · mingforpc/timeexpression · GitHub

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package timeexpression

import "time"

// 从time.go中拷贝出来,私有方法无法导出
// daysBefore[m] counts the number of days in a non-leap year
// before month m begins. There is an entry for m=12, counting
// the number of days before January of next year (365).
var daysBefore = [...]int32{
	0,
	31,
	31 + 28,
	31 + 28 + 31,
	31 + 28 + 31 + 30,
	31 + 28 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30,
	31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 31,
}

func daysIn(m time.Month, year int) int {
	if m == time.February && isLeap(year) {
		return 29
	}
	return int(daysBefore[m] - daysBefore[m-1])
}

func isLeap(year int) bool {
	return year%4 == 0 && (year%100 != 0 || year%400 == 0)
}