Implement date library functions in C++.

src/date.h

+// Copyright 2012 the V8 project authors. All rights reserved.
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+//       notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+#ifndef V8_DATE_H_
+#define V8_DATE_H_
+
+#include "allocation.h"
+#include "globals.h"
+#include "platform.h"
+
+
+namespace v8 {
+namespace internal {
+
+class DateCache {
+ public:
+  static const int kMsPerMin = 60 * 1000;
+  static const int kSecPerDay = 24 * 60 * 60;
+  static const int64_t kMsPerDay = kSecPerDay * 1000;
+
+  // The largest time that can be passed to OS date-time library functions.
+  static const int kMaxEpochTimeInSec = kMaxInt;
+  static const int64_t kMaxEpochTimeInMs =
+      static_cast<int64_t>(kMaxInt) * 1000;
+
+  // The largest time that can be stored in JSDate.
+  static const int64_t kMaxTimeInMs =
+      static_cast<int64_t>(864000000) * 10000000;
+
+  // Sentinel that denotes an invalid local offset.
+  static const int kInvalidLocalOffsetInMs = kMaxInt;
+  // Sentinel that denotes an invalid cache stamp.
+  // It is an invariant of DateCache that cache stamp is non-negative.
+  static const int kInvalidStamp = -1;
+
+  DateCache() : stamp_(0) {
+    ResetDateCache();
+  }
+
+  virtual ~DateCache() {}
+
+
+  // Clears cached timezone information and increments the cache stamp.
+  void ResetDateCache();
+
+
+  // Computes floor(time_ms / kMsPerDay).
+  static int DaysFromTime(int64_t time_ms) {
+    if (time_ms < 0) time_ms -= (kMsPerDay - 1);
+    return static_cast<int>(time_ms / kMsPerDay);
+  }
+
+
+  // Computes modulo(time_ms, kMsPerDay) given that
+  // days = floor(time_ms / kMsPerDay).
+  static int TimeInDay(int64_t time_ms, int days) {
+    return static_cast<int>(time_ms - days * kMsPerDay);
+  }
+
+
+  // Given the number of days since the epoch, computes the weekday.
+  // ECMA 262 - 15.9.1.6.
+  int Weekday(int days) {
+    int result = (days + 4) % 7;
+    return result >= 0 ? result : result + 7;
+  }
+
+
+  bool IsLeap(int year) {
+    return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
+  }
+
+
+  // ECMA 262 - 15.9.1.7.
+  int LocalOffsetInMs() {
+    if (local_offset_ms_ == kInvalidLocalOffsetInMs)  {
+      local_offset_ms_ = GetLocalOffsetFromOS();
+    }
+    return local_offset_ms_;
+  }
+
+
+  const char* LocalTimezone(int64_t time_ms) {
+    if (time_ms < 0 || time_ms > kMaxEpochTimeInMs) {
+      time_ms = EquivalentTime(time_ms);
+    }
+    return OS::LocalTimezone(static_cast<double>(time_ms));
+  }
+
+  // ECMA 262 - 15.9.5.26
+  int TimezoneOffset(int64_t time_ms) {
+    int64_t local_ms = ToLocal(time_ms);
+    return static_cast<int>((time_ms - local_ms) / kMsPerMin);
+  }
+
+  // ECMA 262 - 15.9.1.9
+  int64_t ToLocal(int64_t time_ms) {
+    return time_ms + LocalOffsetInMs() + DaylightSavingsOffsetInMs(time_ms);
+  }
+
+  // ECMA 262 - 15.9.1.9
+  int64_t ToUTC(int64_t time_ms) {
+    time_ms -= LocalOffsetInMs();
+    return time_ms - DaylightSavingsOffsetInMs(time_ms);
+  }
+
+
+  // Computes a time equivalent to the given time according
+  // to ECMA 262 - 15.9.1.9.
+  // The issue here is that some library calls don't work right for dates
+  // that cannot be represented using a non-negative signed 32 bit integer
+  // (measured in whole seconds based on the 1970 epoch).
+  // We solve this by mapping the time to a year with same leap-year-ness
+  // and same starting day for the year. The ECMAscript specification says
+  // we must do this, but for compatibility with other browsers, we use
+  // the actual year if it is in the range 1970..2037
+  int64_t EquivalentTime(int64_t time_ms) {
+    int days = DaysFromTime(time_ms);
+    int time_within_day_ms = static_cast<int>(time_ms - days * kMsPerDay);
+    int year, month, day;
+    YearMonthDayFromDays(days, &year, &month, &day);
+    int new_days = DaysFromYearMonth(EquivalentYear(year), month) + day - 1;
+    return static_cast<int64_t>(new_days) * kMsPerDay + time_within_day_ms;
+  }
+
+  // Returns an equivalent year in the range [2008-2035] matching
+  // - leap year,
+  // - week day of first day.
+  // ECMA 262 - 15.9.1.9.
+  int EquivalentYear(int year) {
+    int week_day = Weekday(DaysFromYearMonth(year, 0));
+    int recent_year = (IsLeap(year) ? 1956 : 1967) + (week_day * 12) % 28;
+    // Find the year in the range 2008..2037 that is equivalent mod 28.
+    // Add 3*28 to give a positive argument to the modulus operator.
+    return 2008 + (recent_year + 3 * 28 - 2008) % 28;
+  }
+
+  // Given the number of days since the epoch, computes
+  // the corresponding year, month, and day.
+  void YearMonthDayFromDays(int days, int* year, int* month, int* day);
+
+  // Computes the number of days since the epoch for
+  // the first day of the given month in the given year.
+  int DaysFromYearMonth(int year, int month);
+
+  // Cache stamp is used for invalidating caches in JSDate.
+  // We increment the stamp each time when the timezone information changes.
+  // JSDate objects perform stamp check and invalidate their caches if
+  // their saved stamp is not equal to the current stamp.
+  Smi* stamp() { return stamp_; }
+  void* stamp_address() { return &stamp_; }
+
+  // These functions are virtual so that we can override them when testing.
+  virtual int GetDaylightSavingsOffsetFromOS(int64_t time_sec) {
+    return static_cast<int>(OS::DaylightSavingsOffset(time_sec * 1000));
+  }
+
+  virtual int GetLocalOffsetFromOS() {
+    double offset = OS::LocalTimeOffset();
+    ASSERT(offset < kInvalidLocalOffsetInMs);
+    return static_cast<int>(offset);
+  }
+
+ private:
+  // The implementation relies on the fact that no time zones have
+  // more than one daylight savings offset change per 19 days.
+  // In Egypt in 2010 they decided to suspend DST during Ramadan. This
+  // led to a short interval where DST is in effect from September 10 to
+  // September 30.
+  static const int kDefaultDSTDeltaInSec = 19 * kSecPerDay;
+
+  // Size of the Daylight Savings Time cache.
+  static const int kDSTSize = 32;
+
+  // Daylight Savings Time segment stores a segment of time where
+  // daylight savings offset does not change.
+  struct DST {
+    int start_sec;
+    int end_sec;
+    int offset_ms;
+    int last_used;
+  };
+
+  // Computes the daylight savings offset for the given time.
+  // ECMA 262 - 15.9.1.8
+  int DaylightSavingsOffsetInMs(int64_t time_ms);
+
+  // Sets the before_ and the after_ segments from the DST cache such that
+  // the before_ segment starts earlier than the given time and
+  // the after_ segment start later than the given time.
+  // Both segments might be invalid.
+  // The last_used counters of the before_ and after_ are updated.
+  void ProbeDST(int time_sec);
+
+  // Finds the least recently used segment from the DST cache that is not
+  // equal to the given 'skip' segment.
+  DST* LeastRecentlyUsedDST(DST* skip);
+
+  // Extends the after_ segment with the given point or resets it
+  // if it starts later than the given time + kDefaultDSTDeltaInSec.
+  inline void ExtendTheAfterSegment(int time_sec, int offset_ms);
+
+  // Makes the given segment invalid.
+  inline void ClearSegment(DST* segment);
+
+  bool InvalidSegment(DST* segment) {
+    return segment->start_sec > segment->end_sec;
+  }
+
+  Smi* stamp_;
+
+  // Daylight Saving Time cache.
+  DST dst_[kDSTSize];
+  int dst_usage_counter_;
+  DST* before_;
+  DST* after_;
+
+  int local_offset_ms_;
+
+  // Year/Month/Day cache.
+  bool ymd_valid_;
+  int ymd_days_;
+  int ymd_year_;
+  int ymd_month_;
+  int ymd_day_;
+};
+
+} }   // namespace v8::internal
+
+#endif