Refactor Date implementation in VM.

runtime/lib/date.dart

Index: runtime/lib/date.dart
diff --git a/runtime/lib/date.dart b/runtime/lib/date.dart
index d39fb8cf92fc4108caf1d4f1583de18d838fc8c2..8112c6278cf6116e46c100273992c3d8391e3a64 100644
--- a/runtime/lib/date.dart
+++ b/runtime/lib/date.dart
@@ -5,7 +5,7 @@
 
 // VM implementation of DateImplementation.
 class DateImplementation implements Date {
-  static final int _SECONDS_YEAR_2035 = 2051222400;
+  static final int _MAX_VALUE = 8640000000000000;
 
   DateImplementation(int years,
                      [int month = 1,
@@ -80,11 +80,14 @@ class DateImplementation implements Date {
   }
 
   DateImplementation.fromEpoch(int this.value, [bool isUtc = false])
-      : _isUtc = isUtc;
+      : _isUtc = isUtc {
+    if (value.abs() > _MAX_VALUE) throw new IllegalArgumentException(value);
+  }
 
   bool operator ==(Object other) {
     if (other is !DateImplementation) return false;
-    return value == other.value;
+    DateImplementation otherDate = other;
+    return value == otherDate.value;
   }
 
   bool operator <(Date other) => value < other.value;
@@ -110,79 +113,56 @@ class DateImplementation implements Date {
 
   String get timeZoneName() {
     if (isUtc()) return "UTC";
-    return _timeZoneName(_equivalentSeconds(_secondsSinceEpoch));
+    return _timeZoneName(value);
   }
 
   Duration get timeZoneOffset() {
     if (isUtc()) return new Duration(0);
-    int offsetInSeconds =
-        _timeZoneOffsetInSeconds(_equivalentSeconds(_secondsSinceEpoch));
+    int offsetInSeconds = _timeZoneOffsetInSeconds(value);
     return new Duration(seconds: offsetInSeconds);
   }
 
   int get year() {
-    int secondsSinceEpoch = _secondsSinceEpoch;
-    // According to V8 some library calls have troubles with negative values.
-    // Therefore clamp to 0 - year 2035 (which is less than the size of 32bit).
-    if (secondsSinceEpoch >= 0 && secondsSinceEpoch < _SECONDS_YEAR_2035) {
-      return _getYear(secondsSinceEpoch, isUtc());
-    }
-
-    // Approximate the result. We don't take timeZone into account.
-    int approximateYear = _yearsFromSecondsSinceEpoch(secondsSinceEpoch);
-    int equivalentYear = _equivalentYear(approximateYear);
-    int y = _getYear(_equivalentSeconds(_secondsSinceEpoch), isUtc());
-    return approximateYear + (y - equivalentYear);
+    return _decomposeIntoYearMonthDay(_localDateInUtcValue)[0];
   }
 
   int get month() {
-    return _getMonth(_equivalentSeconds(_secondsSinceEpoch), isUtc());
+    return _decomposeIntoYearMonthDay(_localDateInUtcValue)[1];
   }
 
   int get day() {
-    return _getDay(_equivalentSeconds(_secondsSinceEpoch), isUtc());
+    return _decomposeIntoYearMonthDay(_localDateInUtcValue)[2];
   }
 
   int get hours() {
-    return _getHours(_equivalentSeconds(_secondsSinceEpoch), isUtc());
+    int valueInHours = _flooredDivision(_localDateInUtcValue,
+                                        Duration.MILLISECONDS_PER_HOUR);
+    return valueInHours % Duration.HOURS_PER_DAY;
   }
 
   int get minutes() {
-    return _getMinutes(_equivalentSeconds(_secondsSinceEpoch), isUtc());
+    int valueInMinutes = _flooredDivision(_localDateInUtcValue,
+                                          Duration.MILLISECONDS_PER_MINUTE);
+    return valueInMinutes % Duration.MINUTES_PER_HOUR;
   }
 
   int get seconds() {
-    return _getSeconds(_equivalentSeconds(_secondsSinceEpoch), isUtc());
+    // Seconds are unaffected by the timezone the user is in. So we can
+    // directly use the value and not the [_localDateInUtcValue].
+    int valueInSeconds =
+        _flooredDivision(value, Duration.MILLISECONDS_PER_SECOND);
+    return valueInSeconds % Duration.SECONDS_PER_MINUTE;
   }
 
   int get milliseconds() {
+    // Milliseconds are unaffected by the timezone the user is in. So we can
+    // directly use the value and not the [_localDateInUtcValue].
     return value % Duration.MILLISECONDS_PER_SECOND;
   }
 
-  int get _secondsSinceEpoch() {
-    // Always round down.
-    if (value < 0) {
-      return (value + 1) ~/ Duration.MILLISECONDS_PER_SECOND - 1;
-    } else {
-      return value ~/ Duration.MILLISECONDS_PER_SECOND;
-    }
-  }
-
   int get weekday() {
-    final Date unixTimeStart = new Date(1970, 1, 1, 0, 0, 0, 0, isUtc());
-    int msSince1970 = this.difference(unixTimeStart).inMilliseconds;
-    // Adjust the milliseconds to avoid problems with summer-time.
-    if (hours < 2) {
-      msSince1970 += 2 * Duration.MILLISECONDS_PER_HOUR;
-    }
-    // Compute the floor of msSince1970 / Duration.MS_PER_DAY.
-    int daysSince1970;
-    if (msSince1970 >= 0) {
-      daysSince1970 = msSince1970 ~/ Duration.MILLISECONDS_PER_DAY;
-    } else {
-      daysSince1970 = (msSince1970 - Duration.MILLISECONDS_PER_DAY + 1) ~/
-                      Duration.MILLISECONDS_PER_DAY;
-    }
+    int daysSince1970 =
+        _flooredDivision(_localDateInUtcValue, Duration.MILLISECONDS_PER_DAY);
     // 1970-1-1 was a Thursday.
     return ((daysSince1970 + Date.THU) % Date.DAYS_IN_WEEK);
   }
@@ -222,27 +202,34 @@ class DateImplementation implements Date {
     }
   }
 
-  // Adds the [duration] to this Date instance.
+  /** Returns a new [Date] with the [duration] added to [this]. */
   Date add(Duration duration) {
     return new DateImplementation.fromEpoch(value + duration.inMilliseconds,
                                             isUtc());
   }
 
-  // Subtracts the [duration] from this Date instance.
+  /** Returns a new [Date] with the [duration] subtracted from [this]. */
   Date subtract(Duration duration) {
     return new DateImplementation.fromEpoch(value - duration.inMilliseconds,
                                             isUtc());
   }
 
-  // Returns a [Duration] with the difference of [this] and [other].
+  /** Returns a [Duration] with the difference of [this] and [other]. */
   Duration difference(Date other) {
     return new DurationImplementation(milliseconds: value - other.value);
   }
 
-  // Returns the UTC year for the corresponding [secondsSinceEpoch].
-  // It is relatively fast for values in the range 0 to year 2098.
+  /** 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]];
+
+  // Returns the UTC year, month and day for the corresponding
+  // [millisecondsSinceEpoch].
   // Code is adapted from V8.
-  static int _yearsFromSecondsSinceEpoch(int secondsSinceEpoch) {
+  static List<int> _decomposeIntoYearMonthDay(int millisecondsSinceEpoch) {
+    // TODO(floitsch): cache result.
     final int DAYS_IN_4_YEARS = 4 * 365 + 1;
     final int DAYS_IN_100_YEARS = 25 * DAYS_IN_4_YEARS - 1;
     final int DAYS_IN_400_YEARS = 4 * DAYS_IN_100_YEARS + 1;
@@ -250,76 +237,143 @@ class DateImplementation implements Date {
     final int DAYS_OFFSET = 1000 * DAYS_IN_400_YEARS + 5 * DAYS_IN_400_YEARS -
                             DAYS_1970_TO_2000;
     final int YEARS_OFFSET = 400000;
-    final int DAYS_YEAR_2098 = DAYS_IN_100_YEARS + 6 * DAYS_IN_4_YEARS;
 
-    int days = secondsSinceEpoch ~/ Duration.SECONDS_PER_DAY;
-    if (days > 0 && days < DAYS_YEAR_2098) {
-      // According to V8 this fast case works for dates from 1970 to 2099.
-      return 1970 + (4 * days + 2) ~/ DAYS_IN_4_YEARS;
-    } else {
-      days += DAYS_OFFSET;
-      int result = 400 * (days ~/ DAYS_IN_400_YEARS) - YEARS_OFFSET;
-      days = days.remainder(DAYS_IN_400_YEARS);
-      days--;
-      int yd1 = days ~/ DAYS_IN_100_YEARS;
-      days = days.remainder(DAYS_IN_100_YEARS);
-      result += 100 * yd1;
-      days++;
-      int yd2 = days ~/ DAYS_IN_4_YEARS;
-      days = days.remainder(DAYS_IN_4_YEARS);
-      result += 4 * yd2;
-      days--;
-      int yd3 = days ~/ 365;
-      days = days.remainder(365);
-      result += yd3;
-      return result;
+    int resultYear = 0;
+    int resultMonth = 0;
+    int resultDay = 0;
+
+    // Always round down.
+    int days = _flooredDivision(millisecondsSinceEpoch,
+                                Duration.MILLISECONDS_PER_DAY);
+    days += DAYS_OFFSET;
+    resultYear = 400 * (days ~/ DAYS_IN_400_YEARS) - YEARS_OFFSET;
+    days = days.remainder(DAYS_IN_400_YEARS);
+    days--;
+    int yd1 = days ~/ DAYS_IN_100_YEARS;
+    days = days.remainder(DAYS_IN_100_YEARS);
+    resultYear += 100 * yd1;
+    days++;
+    int yd2 = days ~/ DAYS_IN_4_YEARS;
+    days = days.remainder(DAYS_IN_4_YEARS);
+    resultYear += 4 * yd2;
+    days--;
+    int yd3 = days ~/ 365;
+    days = days.remainder(365);
+    resultYear += yd3;
+
+    bool isLeap = (yd1 == 0 || yd2 != 0) && yd3 == 0;
+    if (isLeap) days++;
+
+    List<int> daysUntilMonth = _DAYS_UNTIL_MONTH[isLeap ? 1 : 0];
+    for (resultMonth = 12;
+         daysUntilMonth[resultMonth - 1] > days;
+         resultMonth--) {
+      // Do nothing.
     }
+    resultDay = days - daysUntilMonth[resultMonth - 1] + 1;
+    return <int>[resultYear, resultMonth, resultDay];
   }
 
-  // Given [secondsSinceEpoch] returns seconds such that they are at the same
-  // time in an equivalent year (see [_equivalentYear]).
-  // Leap seconds are ignored.
-  static int _equivalentSeconds(int secondsSinceEpoch) {
-    if (secondsSinceEpoch >= 0 && secondsSinceEpoch < _SECONDS_YEAR_2035) {
-      return secondsSinceEpoch;
-    }
-    int year = _yearsFromSecondsSinceEpoch(secondsSinceEpoch);
-    int days = _dayFromYear(year);
-    int equivalentYear = _equivalentYear(year);
-    int equivalentDays = _dayFromYear(equivalentYear);
-    int diffDays = equivalentDays - days;
-    return secondsSinceEpoch + diffDays * Duration.SECONDS_PER_DAY;
+  /**
+   * Returns the amount of milliseconds in UTC that represent the same values as
+   * [this].
+   *
+   * Say [:t:] is the result of this function, then
+   * * [:this.year == new Date.fromEpoch(t, isUtc: true).year:],
+   * * [:this.month == new Date.fromEpoch(t, isUtc: true).month:],
+   * * [:this.day == new Date.fromEpoch(t, isUtc: true).day:],
+   * * [:this.hours == new Date.fromEpoch(t, isUtc: true).hours:],
+   * * ...
+   *
+   * Daylight savings is computed as if the date was computed in [1970..2037].
+   * If [this] lies outside this range then it is a year with similar properties
+   * (leap year, weekdays) is used instead.
+   */
+  int get _localDateInUtcValue() {
+    if (isUtc()) return value;
+    int offset =
+        _timeZoneOffsetInSeconds(value) * Duration.MILLISECONDS_PER_SECOND;
+    return value - offset;
+  }
+
+  static int _flooredDivision(int a, int b) {
+    return (a - (a < 0 ? b - 1 : 0)) ~/ b;
   }
 
   // Returns the days since 1970 for the start of the given [year].
   // [year] may be before epoch.
   static int _dayFromYear(int year) {
-    int flooredDivision(int a, int b) {
-      return (a - (a < 0 ? b - 1 : 0)) ~/ b;
-    }
-
     return 365 * (year - 1970)
-            + flooredDivision(year - 1969, 4)
-            - flooredDivision(year - 1901, 100)
-            + flooredDivision(year - 1601, 400);
+            + _flooredDivision(year - 1969, 4)
+            - _flooredDivision(year - 1901, 100)
+            + _flooredDivision(year - 1601, 400);
   }
 
-  // Returns a year in the range 2008-2035 matching
-  // - leap year, and
-  // - week day of first day.
-  // Leap seconds are ignored.
-  // Adapted from V8's date implementation. See ECMA 262 - 15.9.1.9.
-  static _equivalentYear(int year) {
-    // Returns 1 if in leap year. 0 otherwise.
-    bool inLeapYear(year) {
-      return (year.remainder(4) == 0) &&
-             ((year.remainder(100) != 0) || (year.remainder(400) == 0));
+  static bool _isLeapYear(y) {
+    return (y.remainder(4) == 0) &&
+        ((y.remainder(100) != 0) || (y.remainder(400) == 0));
+  }
+
+  static _brokenDownDateToMillisecondsSinceEpoch(
+      int years, int month, int day,
+      int hours, int minutes, int seconds, int milliseconds,
+      bool isUtc) {
+    if ((month < 1) || (month > 12)) return null;
+    if ((day < 1) || (day > 31)) return null;
+    // Leap seconds can lead to hours == 24.
+    if ((hours < 0) || (hours > 24)) return null;
+    if ((hours == 24) && ((minutes != 0) || (seconds != 0))) return null;
+    if ((minutes < 0) || (minutes > 59)) return null;
+    if ((seconds < 0) || (seconds > 59)) return null;
+    if ((milliseconds < 0) || (milliseconds > 999)) return null;
+
+    // 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);
+    int millisecondsSinceEpoch = days * Duration.MILLISECONDS_PER_DAY +
+        hours * Duration.MILLISECONDS_PER_HOUR +
+        minutes * Duration.MILLISECONDS_PER_MINUTE+
+        seconds * Duration.MILLISECONDS_PER_SECOND +
+        milliseconds;
+
+    // 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_VALUE + Duration.MILLISECONDS_PER_DAY)) {
+      return null;
     }
 
+    if (!isUtc) {
+      // Note that we need to add the local timezone adjustement before asking
+      // for the correct zone offset.
+      int adjustment = _localTimeZoneAdjustmentInSeconds() *
+          Duration.MILLISECONDS_PER_SECOND;
+      int zoneOffset =
+          _timeZoneOffsetInSeconds(millisecondsSinceEpoch + adjustment);
+      millisecondsSinceEpoch += zoneOffset * Duration.MILLISECONDS_PER_SECOND;
+    }
+    if (millisecondsSinceEpoch.abs() > _MAX_VALUE) return null;
+    return millisecondsSinceEpoch;
+  }
+
+  /**
+   * Returns a year in the range 2008-2035 matching
+   * * leap year, and
+   * * week day of first day.
+   *
+   * Leap seconds are ignored.
+   * Adapted from V8's date implementation. See ECMA 262 - 15.9.1.9.
+   */
+  static _equivalentYear(int year) {
     // Returns the week day (in range 0 - 6).
-    int weekDay(year) {
+    int weekDay(y) {
       // 1/1/1970 was a Thursday.
-      return (_dayFromYear(year) + 4) % 7;
+      return (_dayFromYear(y) + 4) % 7;
     }
     // 1/1/1956 was a Sunday (i.e. weekday 0). 1956 was a leap-year.
     // 1/1/1967 was a Sunday (i.e. weekday 0).
@@ -330,82 +384,82 @@ class DateImplementation implements Date {
     // 15 days. 15 % 7 = 1. So after 12 years the week day has always
     // (now independently of leap-years) advanced by one.
     // weekDay * 12 gives thus a year starting with the wanted weekDay.
-    int recentYear = (inLeapYear(year) ? 1956 : 1967) + (weekDay(year) * 12);
+    int recentYear = (_isLeapYear(year) ? 1956 : 1967) + (weekDay(year) * 12);
     // Close to the year 2008 the calendar cycles every 4 * 7 years (4 for the
     // leap years, 7 for the weekdays).
     // Find the year in the range 2008..2037 that is equivalent mod 28.
     return 2008 + (recentYear - 2008) % 28;
   }
 
-  static _brokenDownDateToMillisecondsSinceEpoch(
-      int years, int month, int day,
-      int hours, int minutes, int seconds, int milliseconds,
-      bool isUtc) {
-    if ((month < 1) || (month > 12)) return null;
-    if ((day < 1) || (day > 31)) return null;
-    // Leap seconds can lead to hours == 24.
-    if ((hours < 0) || (hours > 24)) return null;
-    if ((hours == 24) && ((minutes != 0) || (seconds != 0))) return null;
-    if ((minutes < 0) || (minutes > 59)) return null;
-    if ((seconds < 0) || (seconds > 59)) return null;
-    if ((milliseconds < 0) || (milliseconds > 999)) return null;
+  /**
+   * Returns the UTC year for the corresponding [secondsSinceEpoch].
+   * It is relatively fast for values in the range 0 to year 2098.
+   *
+   * Code is adapted from V8.
+   */
+  static int _yearsFromSecondsSinceEpoch(int secondsSinceEpoch) {
+    final int DAYS_IN_4_YEARS = 4 * 365 + 1;
+    final int DAYS_IN_100_YEARS = 25 * DAYS_IN_4_YEARS - 1;
+    final int DAYS_YEAR_2098 = DAYS_IN_100_YEARS + 6 * DAYS_IN_4_YEARS;
 
-    int equivalentYear;
-    int offsetInSeconds;
-    // According to V8 some library calls have troubles with negative values.
-    // Therefore clamp to 1970 - year 2035 (which is less than the size of
-    // 32bit).
-    // We exclude the year 1970 when the time is not UTC, since the epoch
-    // value could then be negative.
-    if (years < (isUtc ? 1970 : 1971) || years > 2035) {
-      equivalentYear = _equivalentYear(years);
-      int offsetInDays = (_dayFromYear(years) - _dayFromYear(equivalentYear));
-      // Leap seconds are ignored.
-      offsetInSeconds = offsetInDays * Duration.SECONDS_PER_DAY;
-    } else {
-      equivalentYear = years;
-      offsetInSeconds = 0;
+    int days = secondsSinceEpoch ~/ Duration.SECONDS_PER_DAY;
+    if (days > 0 && days < DAYS_YEAR_2098) {
+      // According to V8 this fast case works for dates from 1970 to 2099.
+      return 1970 + (4 * days + 2) ~/ DAYS_IN_4_YEARS;
     }
-    int secondsSinceEpoch = _brokenDownDateToSecondsSinceEpoch(
-        equivalentYear, month, day, hours, minutes, seconds, isUtc);
-    int adjustedSeconds = secondsSinceEpoch + offsetInSeconds;
-    return adjustedSeconds * Duration.MILLISECONDS_PER_SECOND + milliseconds;
+    int ms = secondsSinceEpoch * Duration.MILLISECONDS_PER_SECOND;
+    return _decomposeIntoYearMonthDay(ms)[0];
+  }
+
+  /**
+   * Returns a date in seconds that is equivalent to the current date. An
+   * equivalent date has the same fields ([:month:], [:day:], etc.) as the
+   * [this], but the [:year:] is in the range [1970..2037].
+   *
+   * * The time since the beginning of the year is the same.
+   * * If [this] is in a leap year then the returned seconds are in a leap
+   *   year, too.
+   * * The week day of [this] is the same as the one for the returned date.
+   */
+  static int _equivalentSeconds(int millisecondsSinceEpoch) {
+    final int CUT_OFF_SECONDS = 2100000000;
+
+    int secondsSinceEpoch = _flooredDivision(millisecondsSinceEpoch,
+                                             Duration.MILLISECONDS_PER_SECOND);
+
+    if (secondsSinceEpoch < 0 || secondsSinceEpoch >= CUT_OFF_SECONDS) {
+      int year = _yearsFromSecondsSinceEpoch(secondsSinceEpoch);
+      int days = _dayFromYear(year);
+      int equivalentYear = _equivalentYear(year);
+      int equivalentDays = _dayFromYear(equivalentYear);
+      int diffDays = equivalentDays - days;
+      secondsSinceEpoch += diffDays * Duration.SECONDS_PER_DAY;
+    }
+    return secondsSinceEpoch;
+  }
+
+  static int _timeZoneOffsetInSeconds(int millisecondsSinceEpoch) {
+    int equivalentSeconds = _equivalentSeconds(millisecondsSinceEpoch);
+    return _timeZoneOffsetInSecondsForClampedSeconds(equivalentSeconds);
+  }
+
+  static String _timeZoneName(int millisecondsSinceEpoch) {
+    int equivalentSeconds = _equivalentSeconds(millisecondsSinceEpoch);
+    return _timeZoneNameForClampedSeconds(equivalentSeconds);
   }
 
   final bool _isUtc;
   final int value;
 
-
   // Natives
-  static _brokenDownDateToSecondsSinceEpoch(
-      int years, int month, int day, int hours, int minutes, int seconds,
-      bool isUtc) native "DateNatives_brokenDownToSecondsSinceEpoch";
-
   static int _getCurrentMs() native "DateNatives_currentTimeMillis";
 
-  static String _timeZoneName(int secondsSinceEpoch)
+  static String _timeZoneNameForClampedSeconds(int secondsSinceEpoch)
       native "DateNatives_timeZoneName";
 
-  static int _timeZoneOffsetInSeconds(int secondsSinceEpoch)
+  static int _timeZoneOffsetInSecondsForClampedSeconds(int secondsSinceEpoch)
       native "DateNatives_timeZoneOffsetInSeconds";
 
-  // TODO(floitsch): it would be more efficient if we didn't call the native
-  // function for every member, but cached the broken-down date.
-  static int _getYear(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getYear";
-
-  static int _getMonth(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getMonth";
-
-  static int _getDay(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getDay";
-
-  static int _getHours(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getHours";
-
-  static int _getMinutes(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getMinutes";
-
-  static int _getSeconds(int secondsSinceEpoch, bool isUtc)
-      native "DateNatives_getSeconds";
+  static int _localTimeZoneAdjustmentInSeconds()
+      native "DateNatives_localTimeZoneAdjustmentInSeconds";
 }