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..6a3dfb724f7a4e2a972a6b5d60c31f359ba9b964 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 +246,8 @@ 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],
+             const [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366]];

[floitsch, 2012/08/06 21:00:58]

80chars.

[dominich, 2012/08/06 21:20:58]

Done.

 
   // Returns the UTC year, month and day for the corresponding
   // [millisecondsSinceEpoch].
@@ -340,23 +340,53 @@ 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;
+    // Deal with under and overflow.
+    second += (millisecond / 1000).floor().toInt();
+    millisecond = millisecond % 1000;
+    minute += (second / 60).floor().toInt();
+    second = second % 60;
+    hour += (minute / 60).floor().toInt();
+    minute = minute % 60;
+    day += (hour / 24).floor().toInt();
+    hour = hour % 24;
+    year += ((month - 1) / 12).floor().toInt();
+    month = (month - 1) % 12 + 1;
+
+    // Start with the current month and add _DAYS_UNTIL_MONTH until day > 1
+    // (and <= numDaysInMonth).
+    while (day < 1) {
+      int numDaysInMonth = _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month] -
+          _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month - 1];
+      day += numDaysInMonth;
+      --month;
+      if (month < 1) {
+        --year;
+        month = 12;
+      }
+    }
+
+    // And in reverse.
+    int numDaysInMonth = _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month] -
+        _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month - 1];
+    while (day > numDaysInMonth) {
+      day -= numDaysInMonth;
+      ++month;
+      if (month > 12) {
+        ++year;
+        month = 1;
+      }
+      numDaysInMonth = _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month] -
+          _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month - 1];
+    }
 
     // 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];

[floitsch, 2012/08/06 21:00:58]

Isn't it enough to:
years += (month - 1) ~/ 12;
int clampedMonth = (month - 1).remainder(12);
if (clampedMonth < 0) { years--; clampedMonth += 12; }

The hour, minute, second and milliseconds are correctly added later and don't
depend on the month/year anyways.

[dominich, 2012/08/06 21:20:58]

No - clampedMonth could be -50 in which case years should be decremented
further.

[floitsch, 2012/08/07 09:10:07]

I don't see how this could happen since it is .remainder(12).

[dominich, 2012/08/13 19:26:35]

i've just realised - i'm not sure which bit of the code you're suggesting
replacing. The comment is under the day loop (that needs to evaluate every
month) and the code above that changes the years/months is just a divide and
floor, rather than the remainder, and doesn't have the branch.

why would your suggestion be better, and which bit of the code is it suggested
to improve?

[floitsch, 2012/08/13 19:41:34]

Unless I'm wrong you don't need to do any loops. The beginning of this function
could be:
_brokenDown...(int year, ...) {
  // First compute the seconds ...
  years += (month - 1) ~/ 12;
  int clampedMonth = (month - 1).remainder(12);
  if (clampedMonth < 0) { years--; clampedMonth += 12; }
  int days = day - 1;
  days += _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][clampedMonth - 1];
  days += _dayFromYear(year);
  ... // same as before.

-    days += _dayFromYear(years);
+    days += _DAYS_UNTIL_MONTH[_isLeapYear(year) ? 1 : 0][month - 1];
+    days += _dayFromYear(year);
     int millisecondsSinceEpoch = days * Duration.MILLISECONDS_PER_DAY +
         hour * Duration.MILLISECONDS_PER_HOUR +
         minute * Duration.MILLISECONDS_PER_MINUTE+