[WIP][SPARK-31579][SQL] Floor div to div

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/RebaseDateTime.scala

@@ -188,6 +188,27 @@ object RebaseDateTime {
     Math.toIntExact(Math.floorDiv(utcCal.getTimeInMillis, MILLIS_PER_DAY))
   }
 
+  private[sql] def POC_localRebaseGregorianToJulianDays(tz: TimeZone, days: Int,
+        hour: Int, div: Boolean): Int = {
+    var localDate = LocalDate.ofEpochDay(days)
+    if (localDate.isAfter(julianEndDate) && localDate.isBefore(gregorianStartDate)) {
+      localDate = gregorianStartDate
+    }
+    val utcCal = new Calendar.Builder()
+      // `gregory` is a hybrid calendar that supports both
+      // the Julian and Gregorian calendar systems
+      .setCalendarType("gregory")
+      .setTimeZone(tz)
+      .setDate(localDate.getYear, localDate.getMonthValue - 1, localDate.getDayOfMonth)
+      .setTimeOfDay(hour, 0, 0)
+      .build()
+    if (div) {
+      Math.toIntExact(utcCal.getTimeInMillis/MILLIS_PER_DAY)
+    } else {
+      Math.toIntExact(Math.floorDiv(utcCal.getTimeInMillis, MILLIS_PER_DAY))
+    }
+  }
+
   /**
    * An optimized version of [[localRebaseGregorianToJulianDays(Int)]]. This method leverages the
    * pre-calculated rebasing array to save calculation. For dates of Before Common Era, the
@@ -204,6 +225,14 @@ object RebaseDateTime {
     }
   }
 
+def POC_rebaseGregorianToJulianDays(tz: TimeZone, days: Int,
+        hour: Int, div: Boolean): Int = {
+    if (days < gregorianCommonEraStartDay) {
+      POC_localRebaseGregorianToJulianDays(tz, days, hour, div)
+    } else {
+      rebaseDays(gregJulianDiffSwitchDay, gregJulianDiffs, days)
+    }
+  }
 
   /**
    * The class describes JSON records with microseconds rebasing info.

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/util/RebaseDateTimeSuite.scala

@@ -167,6 +167,19 @@ class RebaseDateTimeSuite extends SparkFunSuite with Matchers with SQLHelper {
     }
   }
 
+  test("SPARK-31579: Replace floorDiv by / in localRebaseGregorianToJulianDays()") {
+    val start = localDateToDays(LocalDate.of(1, 1, 1))
+    val end = localDateToDays(LocalDate.of(2100, 1, 1))
+    for (tz <- TimeZone.getAvailableIDs()) {
+      for (day <- start to end) {
+        for (hr <- List.range(0, 24)) {
+          assert(POC_rebaseGregorianToJulianDays(TimeZone.getTimeZone(tz), day, hr, false) ===
+          POC_rebaseGregorianToJulianDays(TimeZone.getTimeZone(tz), day, hr, true))
+        }
+      }
+    }
+  }
+
   test("SPARK-31328: rebasing overlapped timestamps during daylight saving time") {
     Seq(
       LA.getId -> Seq("2019-11-03T08:00:00Z", "2019-11-03T08:30:00Z", "2019-11-03T09:00:00Z"),