Optimize DateTime constructor slightly.

runtime/lib/date_patch.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Dart core library.
 
 // VM implementation of DateTime.
 patch class DateTime {
   // Natives.
   // The natives have been moved up here to work around Issue 10401.
   static int _getCurrentMs() native "DateNatives_currentTimeMillis";
@@ skipping 129 matching lines @@
     return list;
   }
 
   get _parts {
     if (__parts == null) {
       __parts = _computeUpperPart(_localDateInUtcMs);
     }
     return __parts;
   }
 
-  /* patch */ int get millisecond => _parts[_MILLISECOND_INDEX];
+  /* patch */ int get millisecond => __[_MILLISECOND_INDEX];

[Søren Gjesse, 2015/01/07 10:48:18]

Where does __ come from?

[Lasse Reichstein Nielsen, 2015/01/07 12:01:19]

Ack, bad edit.

[Søren Gjesse, 2015/01/07 12:03:29]

Thought so :-)

 
   /* patch */ int get second => _parts[_SECOND_INDEX];
 
   /* patch */ int get minute => _parts[_MINUTE_INDEX];
 
   /* patch */ int get hour => _parts[_HOUR_INDEX];
 
   /* patch */ int get day => _parts[_DAY_INDEX];
 
   /* patch */ int get weekday => _parts[_WEEKDAY_INDEX];
@@ skipping 32 matching lines @@
   // Returns the days since 1970 for the start of the given [year].
   // [year] may be before epoch.
   static int _dayFromYear(int year) {
     return 365 * (year - 1970)
             + _flooredDivision(year - 1969, 4)
             - _flooredDivision(year - 1901, 100)
             + _flooredDivision(year - 1601, 400);
   }
 
   static bool _isLeapYear(y) {
-    return (y.remainder(4) == 0) &&
-        ((y.remainder(100) != 0) || (y.remainder(400) == 0));
+    // (y % 16 == 0) matches multiples of 400, and is faster than % 400.
+    return (y % 4 == 0) && ((y % 16 == 0) || (y % 100 != 0));
   }
 
   /* patch */ static int _brokenDownDateToMillisecondsSinceEpoch(
       int year, int month, int day,
       int hour, int minute, int second, int millisecond,
       bool isUtc) {
     // Simplify calculations by working with zero-based month.
     --month;
     // Deal with under and overflow.
-    year += (month / 12).floor();
-    month = month % 12;
+    if (month >= 12) {
+      year += month ~/ 12;
+      month = month % 12;
+    } else if (month < 0) {
+      int realMonth = month % 12;
+      year += (month - realMonth) ~/ 12;
+      month = realMonth;
+    }
 
     // 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(year) ? 1 : 0][month];
     days += _dayFromYear(year);
-    int millisecondsSinceEpoch = days * Duration.MILLISECONDS_PER_DAY +
-        hour * Duration.MILLISECONDS_PER_HOUR +
-        minute * Duration.MILLISECONDS_PER_MINUTE+
+    int millisecondsSinceEpoch =
+        days   * Duration.MILLISECONDS_PER_DAY    +
+        hour   * Duration.MILLISECONDS_PER_HOUR   +
+        minute * Duration.MILLISECONDS_PER_MINUTE +
         second * Duration.MILLISECONDS_PER_SECOND +
         millisecond;
 
     // Since [_timeZoneOffsetInSeconds] will crash if the input is far out of
     // the valid range we do a preliminary test that weeds out values that can
     // not become valid even with timezone adjustments.
     // The timezone adjustment is always less than a day, so adding a security
     // margin of one day should be enough.
     if (millisecondsSinceEpoch.abs() >
         (_MAX_MILLISECONDS_SINCE_EPOCH + Duration.MILLISECONDS_PER_DAY)) {
@@ skipping 96 matching lines @@
   static int _timeZoneOffsetInSeconds(int millisecondsSinceEpoch) {
     int equivalentSeconds = _equivalentSeconds(millisecondsSinceEpoch);
     return _timeZoneOffsetInSecondsForClampedSeconds(equivalentSeconds);
   }
 
   static String _timeZoneName(int millisecondsSinceEpoch) {
     int equivalentSeconds = _equivalentSeconds(millisecondsSinceEpoch);
     return _timeZoneNameForClampedSeconds(equivalentSeconds);
   }
 }