Updated VM and JS versions of Date to allow underflow and overflow.

runtime/lib/date.dart

Index: runtime/lib/date.dart
diff --git a/runtime/lib/date.dart b/runtime/lib/date.dart
index 71c079fa7b6e40c1ed5d2b10b0efce6c3a5cc51a..18c3bef8305936b46e5ac82deff2f2bac323281e 100644
--- a/runtime/lib/date.dart
+++ b/runtime/lib/date.dart
@@ -7,7 +7,7 @@
 class DateImplementation implements Date {
   static final int _MAX_MILLISECONDS_SINCE_EPOCH = 8640000000000000;
 
-  DateImplementation(int years,
+  DateImplementation(int year,
                      [int month = 1,
                       int day = 1,
                       int hour = 0,
@@ -17,7 +17,7 @@ class DateImplementation implements Date {
                       bool isUtc = false])
       : this.isUtc = isUtc,
         this.millisecondsSinceEpoch = _brokenDownDateToMillisecondsSinceEpoch(
-            years, month, day, hour, minute, second, millisecond, isUtc) {
+            year, month, day, hour, minute, second, millisecond, isUtc) {
     if (millisecondsSinceEpoch === null) throw new IllegalArgumentException();
     if (isUtc === null) throw new IllegalArgumentException();
   }
@@ -54,7 +54,7 @@ class DateImplementation implements Date {
         return Math.parseDouble(matched);
       }
 
-      int years = Math.parseInt(match[1]);
+      int year = Math.parseInt(match[1]);
       int month = Math.parseInt(match[2]);
       int day = Math.parseInt(match[3]);
       int hour = parseIntOrZero(match[4]);
@@ -69,7 +69,7 @@ class DateImplementation implements Date {
       // TODO(floitsch): we should not need to test against the empty string.
       bool isUtc = (match[8] !== null) && (match[8] != "");
       int millisecondsSinceEpoch = _brokenDownDateToMillisecondsSinceEpoch(
-          years, month, day, hour, minute, second, millisecond, isUtc);
+          year, month, day, hour, minute, second, millisecond, isUtc);
       if (millisecondsSinceEpoch === null) {
         throw new IllegalArgumentException(formattedString);
       }
@@ -246,8 +246,9 @@ class DateImplementation implements Date {
   /** The first list contains the days until each month in non-leap years. The
     * second list contains the days in leap years. */
   static final List<List<int>> _DAYS_UNTIL_MONTH =
-      const [const [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334],
-             const [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335]];
+      const [
+          const [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365],

[floitsch, 2012/08/15 08:44:26]

No need for the additional days anymore.

[dominich, 2012/08/17 16:38:33]

Done.

+          const [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366]];
 
   // Returns the UTC year, month and day for the corresponding
   // [millisecondsSinceEpoch].
@@ -340,23 +341,26 @@ class DateImplementation implements Date {
   }
 
   static _brokenDownDateToMillisecondsSinceEpoch(
-      int years, int month, int day,
+      int year, int month, int day,
       int hour, int minute, int second, int millisecond,
       bool isUtc) {
-    if ((month < 1) || (month > 12)) return null;
-    if ((day < 1) || (day > 31)) return null;
-    // Leap seconds can lead to hour == 24.
-    if ((hour < 0) || (hour > 24)) return null;
-    if ((hour == 24) && ((minute != 0) || (second != 0))) return null;
-    if ((minute < 0) || (minute > 59)) return null;
-    if ((second < 0) || (second > 59)) return null;
-    if ((millisecond < 0) || (millisecond > 999)) return null;
+    // JavaScript month is zero-based while Dart is one-based. This should
+    // simplify some calculations.
+    --month;
+    // Deal with under and overflow.
+    year += (month / 12).floor().toInt();
+    month = month % 12;
+    int clampedMonth = month.remainder(12);
+    if (clampedMonth < 0) {
+      --year;
+      clampedMonth += 12;
+    }
 
     // First compute the seconds in UTC, independent of the [isUtc] flag. If
     // necessary we will add the time-zone offset later on.
     int days = day - 1;
-    days += _DAYS_UNTIL_MONTH[_isLeapYear(years) ? 1 : 0][month - 1];
-    days += _dayFromYear(years);
+    days += _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][clampedMonth];
+    days += _dayFromYear(year);
     int millisecondsSinceEpoch = days * Duration.MILLISECONDS_PER_DAY +
         hour * Duration.MILLISECONDS_PER_HOUR +
         minute * Duration.MILLISECONDS_PER_MINUTE+