fix #1499 rounding for timestamps truncated to dates before 1970 (#1502)

* fix #1499 rounding for timestamps truncated to dates before 1970

* Implement floorDiv until we drop support for Java 1.7

pgjdbc/src/main/java/org/postgresql/jdbc/TimestampUtils.java

@@ -1232,7 +1232,12 @@ public Date convertToDate(long millis, TimeZone tz) {
     if (tz == null) {
       tz = getDefaultTz();
     }
-    if (isSimpleTimeZone(tz.getID())) {
+    /*
+    the following math does not work for negative times
+    Punt and use Calendar for negative times.
+    This probably introduces a performance regression for times before 1970
+     */
+    if ( isSimpleTimeZone(tz.getID())) {
       // Truncate to 00:00 of the day.
       // Suppose the input date is 7 Jan 15:40 GMT+02:00 (that is 13:40 UTC)
       // We want it to become 7 Jan 00:00 GMT+02:00
@@ -1241,20 +1246,22 @@ public Date convertToDate(long millis, TimeZone tz) {
       millis += offset;
       // 2) Truncate hours, minutes, etc. Day is always 86400 seconds, no matter what leap seconds
       // are
-      millis = millis / ONEDAY * ONEDAY;
+      millis = floorDiv(millis, ONEDAY) * ONEDAY;
       // 2) Now millis is 7 Jan 00:00 UTC, however we need that in GMT+02:00, so subtract some
       // offset
       millis -= offset;
       // Now we have brand-new 7 Jan 00:00 GMT+02:00
       return new Date(millis);
     }
+
     Calendar cal = calendarWithUserTz;
     cal.setTimeZone(tz);
     cal.setTimeInMillis(millis);
     cal.set(Calendar.HOUR_OF_DAY, 0);
     cal.set(Calendar.MINUTE, 0);
     cal.set(Calendar.SECOND, 0);
     cal.set(Calendar.MILLISECOND, 0);
+
     return new Date(cal.getTimeInMillis());
   }
 
@@ -1411,4 +1418,16 @@ public static TimeZone parseBackendTimeZone(String timeZone) {
     }
     return TimeZone.getTimeZone(timeZone);
   }
+
+  /*
+  provide our own as this is not available until 1.8
+   */
+  public static long floorDiv(long x, long y) {
+    long r = x / y;
+    // if the signs are different and modulo not zero, round down
+    if ((x ^ y) < 0 && (r * y != x)) {
+      r--;
+    }
+    return r;
+  }
 }

pgjdbc/src/test/java/org/postgresql/test/jdbc2/TimestampTest.java

@@ -47,6 +47,8 @@ public TimestampTest(BinaryMode binaryMode) {
     setBinaryMode(binaryMode);
   }
 
+  private TimeZone currentTZ;
+
   @Parameterized.Parameters(name = "binary = {0}")
   public static Iterable<Object[]> data() {
     Collection<Object[]> ids = new ArrayList<Object[]>();
@@ -62,13 +64,15 @@ public void setUp() throws Exception {
     TestUtil.createTable(con, TSWTZ_TABLE, "ts timestamp with time zone");
     TestUtil.createTable(con, TSWOTZ_TABLE, "ts timestamp without time zone");
     TestUtil.createTable(con, DATE_TABLE, "ts date");
+    currentTZ = TimeZone.getDefault();
   }
 
   @Override
   public void tearDown() throws SQLException {
     TestUtil.dropTable(con, TSWTZ_TABLE);
     TestUtil.dropTable(con, TSWOTZ_TABLE);
     TestUtil.dropTable(con, DATE_TABLE);
+    TimeZone.setDefault(currentTZ);
     super.tearDown();
   }
 
@@ -555,6 +559,22 @@ public void testSetTimestampWOTZ() throws SQLException {
     stmt.close();
   }
 
+  /*
+  Times before 1970 are negative in Java.
+  the convert to date does some math that assumes times are positive.
+  This test assures that the convertToDate still works properly with negative times
+   */
+  @Test
+  public void TestTimeStampBefore1970() {
+
+    TimeZone.setDefault(TimeZone.getTimeZone("UTC"));
+    TimestampUtils tsu = ((BaseConnection) con).getTimestampUtils();
+
+    Date date = tsu.convertToDate(Timestamp.valueOf("1969-01-10 12:00:00").getTime(), TimeZone.getDefault());
+
+    assertEquals(new GregorianCalendar(1969, Calendar.JANUARY, 10).getTime().getTime(), date.getTime() );
+  }
+
   /*
    * Helper for the TimestampTests. It tests what should be in the db
    */