Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/7754#discussion_r35822048
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/DateTimeUtils.scala
---
@@ -575,6 +576,138 @@ object DateTimeUtils {
}
/**
+ * The number of days for each month (not leap year)
+ */
+ private val monthDays = Array(31, 28, 31, 30, 31, 30, 31, 31, 30, 31,
30, 31)
+
+ /**
+ * Returns the date value for the first day of the given month.
+ * The month is expressed in months since year zero (17999 BC), starting
from 0.
+ */
+ private def firstDayOfMonth(absoluteMonth: Int): Int = {
+ val absoluteYear = absoluteMonth / 12
+ var monthInYear = absoluteMonth - absoluteYear * 12
+ var days = getDaysFromYears(absoluteYear)
+ if (monthInYear >= 2 && isLeapYear(absoluteYear + YearZero)) {
+ days += 1
+ }
+ while (monthInYear > 0) {
+ days += monthDays(monthInYear - 1)
+ monthInYear -= 1
+ }
+ days
+ }
+
+ /**
+ * Returns the date value for January 1 of the given year.
+ * The year is expressed in years since year zero (17999 BC), starting
from 0.
+ */
+ private def getDaysFromYears(absoluteYear: Int): Int = {
+ val absoluteDays = (absoluteYear * 365 + absoluteYear / 400 -
absoluteYear / 100
+ + absoluteYear / 4)
+ absoluteDays - toYearZero
+ }
+
+ /**
+ * Add date and year-month interval.
+ * Returns a date value, expressed in days since 1.1.1970.
+ */
+ def dateAddMonths(days: Int, months: Int): Int = {
+ val absoluteMonth = (getYear(days) - YearZero) * 12 + getMonth(days) -
1 + months
+ val currentMonthInYear = absoluteMonth % 12
+ val currentYear = absoluteMonth / 12
+ val leapDay = if (currentMonthInYear == 1 && isLeapYear(currentYear +
YearZero)) 1 else 0
+ val lastDayOfMonth = monthDays(currentMonthInYear) + leapDay
+
+ val dayOfMonth = getDayOfMonth(days)
+ val currentDayInMonth = if (getDayOfMonth(days + 1) == 1 || dayOfMonth
>= lastDayOfMonth) {
+ // last day of the month
+ lastDayOfMonth
+ } else {
+ dayOfMonth
+ }
+ firstDayOfMonth(absoluteMonth) + currentDayInMonth - 1
+ }
+
+ /**
+ * Add timestamp and full interval.
+ * Returns a timestamp value, expressed in microseconds since 1.1.1970
00:00:00.
+ */
+ def timestampAddInterval(start: Long, months: Int, microseconds: Long):
Long = {
+ val days = millisToDays(start / 1000L)
+ val newDays = dateAddMonths(days, months)
+ daysToMillis(newDays) * 1000L + start - daysToMillis(days) * 1000L +
microseconds
+ }
+
+ /**
+ * Returns the last dayInMonth in the month it belongs to. The date is
expressed
+ * in days since 1.1.1970. the return value starts from 1.
+ */
+ private def getLastDayInMonthOfMonth(date: Int): Int = {
+ var (year, dayInYear) = getYearAndDayInYear(date)
+ if (isLeapYear(year)) {
+ if (dayInYear > 31 && dayInYear <= 60) {
+ return 29
+ } else if (dayInYear > 60) {
+ dayInYear = dayInYear - 1
+ }
+ }
+ if (dayInYear <= 31) {
+ 31
+ } else if (dayInYear <= 59) {
+ 28
+ } else if (dayInYear <= 90) {
+ 31
+ } else if (dayInYear <= 120) {
+ 30
+ } else if (dayInYear <= 151) {
+ 31
+ } else if (dayInYear <= 181) {
+ 30
+ } else if (dayInYear <= 212) {
+ 31
+ } else if (dayInYear <= 243) {
+ 31
+ } else if (dayInYear <= 273) {
+ 30
+ } else if (dayInYear <= 304) {
+ 31
+ } else if (dayInYear <= 334) {
+ 30
+ } else {
+ 31
+ }
+ }
+
+ /**
+ * Returns number of months between time1 and time2. time1 and time2 are
expressed in
+ * microseconds since 1.1.1970
--- End diff --
we should document that this returns an integer if it is the same day in
each month
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