1 // Copyright 2012 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
8 #include "src/allocation.h"
9 #include "src/base/platform/platform.h"
10 #include "src/globals.h"
18 static const int kMsPerMin = 60 * 1000;
19 static const int kSecPerDay = 24 * 60 * 60;
20 static const int64_t kMsPerDay = kSecPerDay * 1000;
22 // The largest time that can be passed to OS date-time library functions.
23 static const int kMaxEpochTimeInSec = kMaxInt;
24 static const int64_t kMaxEpochTimeInMs =
25 static_cast<int64_t>(kMaxInt) * 1000;
27 // The largest time that can be stored in JSDate.
28 static const int64_t kMaxTimeInMs =
29 static_cast<int64_t>(864000000) * 10000000;
31 // Conservative upper bound on time that can be stored in JSDate
32 // before UTC conversion.
33 static const int64_t kMaxTimeBeforeUTCInMs =
34 kMaxTimeInMs + 10 * kMsPerDay;
36 // Sentinel that denotes an invalid local offset.
37 static const int kInvalidLocalOffsetInMs = kMaxInt;
38 // Sentinel that denotes an invalid cache stamp.
39 // It is an invariant of DateCache that cache stamp is non-negative.
40 static const int kInvalidStamp = -1;
42 DateCache() : stamp_(0), tz_cache_(base::OS::CreateTimezoneCache()) {
46 virtual ~DateCache() {
47 base::OS::DisposeTimezoneCache(tz_cache_);
52 // Clears cached timezone information and increments the cache stamp.
53 void ResetDateCache();
56 // Computes floor(time_ms / kMsPerDay).
57 static int DaysFromTime(int64_t time_ms) {
58 if (time_ms < 0) time_ms -= (kMsPerDay - 1);
59 return static_cast<int>(time_ms / kMsPerDay);
63 // Computes modulo(time_ms, kMsPerDay) given that
64 // days = floor(time_ms / kMsPerDay).
65 static int TimeInDay(int64_t time_ms, int days) {
66 return static_cast<int>(time_ms - days * kMsPerDay);
70 // Given the number of days since the epoch, computes the weekday.
71 // ECMA 262 - 15.9.1.6.
72 int Weekday(int days) {
73 int result = (days + 4) % 7;
74 return result >= 0 ? result : result + 7;
78 bool IsLeap(int year) {
79 return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
83 // ECMA 262 - 15.9.1.7.
84 int LocalOffsetInMs() {
85 if (local_offset_ms_ == kInvalidLocalOffsetInMs) {
86 local_offset_ms_ = GetLocalOffsetFromOS();
88 return local_offset_ms_;
92 const char* LocalTimezone(int64_t time_ms) {
93 if (time_ms < 0 || time_ms > kMaxEpochTimeInMs) {
94 time_ms = EquivalentTime(time_ms);
96 return base::OS::LocalTimezone(static_cast<double>(time_ms), tz_cache_);
99 // ECMA 262 - 15.9.5.26
100 int TimezoneOffset(int64_t time_ms) {
101 int64_t local_ms = ToLocal(time_ms);
102 return static_cast<int>((time_ms - local_ms) / kMsPerMin);
105 // ECMA 262 - 15.9.1.9
106 // LocalTime(t) = t + LocalTZA + DaylightSavingTA(t)
107 // ECMA 262 assumes that DaylightSavingTA is computed using UTC time,
108 // but we fetch DST from OS using local time, therefore we need:
109 // LocalTime(t) = t + LocalTZA + DaylightSavingTA(t + LocalTZA).
110 int64_t ToLocal(int64_t time_ms) {
111 time_ms += LocalOffsetInMs();
112 return time_ms + DaylightSavingsOffsetInMs(time_ms);
115 // ECMA 262 - 15.9.1.9
116 // UTC(t) = t - LocalTZA - DaylightSavingTA(t - LocalTZA)
117 // ECMA 262 assumes that DaylightSavingTA is computed using UTC time,
118 // but we fetch DST from OS using local time, therefore we need:
119 // UTC(t) = t - LocalTZA - DaylightSavingTA(t).
120 int64_t ToUTC(int64_t time_ms) {
121 return time_ms - LocalOffsetInMs() - DaylightSavingsOffsetInMs(time_ms);
125 // Computes a time equivalent to the given time according
126 // to ECMA 262 - 15.9.1.9.
127 // The issue here is that some library calls don't work right for dates
128 // that cannot be represented using a non-negative signed 32 bit integer
129 // (measured in whole seconds based on the 1970 epoch).
130 // We solve this by mapping the time to a year with same leap-year-ness
131 // and same starting day for the year. The ECMAscript specification says
132 // we must do this, but for compatibility with other browsers, we use
133 // the actual year if it is in the range 1970..2037
134 int64_t EquivalentTime(int64_t time_ms) {
135 int days = DaysFromTime(time_ms);
136 int time_within_day_ms = static_cast<int>(time_ms - days * kMsPerDay);
137 int year, month, day;
138 YearMonthDayFromDays(days, &year, &month, &day);
139 int new_days = DaysFromYearMonth(EquivalentYear(year), month) + day - 1;
140 return static_cast<int64_t>(new_days) * kMsPerDay + time_within_day_ms;
143 // Returns an equivalent year in the range [2008-2035] matching
145 // - week day of first day.
146 // ECMA 262 - 15.9.1.9.
147 int EquivalentYear(int year) {
148 int week_day = Weekday(DaysFromYearMonth(year, 0));
149 int recent_year = (IsLeap(year) ? 1956 : 1967) + (week_day * 12) % 28;
150 // Find the year in the range 2008..2037 that is equivalent mod 28.
151 // Add 3*28 to give a positive argument to the modulus operator.
152 return 2008 + (recent_year + 3 * 28 - 2008) % 28;
155 // Given the number of days since the epoch, computes
156 // the corresponding year, month, and day.
157 void YearMonthDayFromDays(int days, int* year, int* month, int* day);
159 // Computes the number of days since the epoch for
160 // the first day of the given month in the given year.
161 int DaysFromYearMonth(int year, int month);
163 // Cache stamp is used for invalidating caches in JSDate.
164 // We increment the stamp each time when the timezone information changes.
165 // JSDate objects perform stamp check and invalidate their caches if
166 // their saved stamp is not equal to the current stamp.
167 Smi* stamp() { return stamp_; }
168 void* stamp_address() { return &stamp_; }
170 // These functions are virtual so that we can override them when testing.
171 virtual int GetDaylightSavingsOffsetFromOS(int64_t time_sec) {
172 double time_ms = static_cast<double>(time_sec * 1000);
173 return static_cast<int>(
174 base::OS::DaylightSavingsOffset(time_ms, tz_cache_));
177 virtual int GetLocalOffsetFromOS() {
178 double offset = base::OS::LocalTimeOffset(tz_cache_);
179 DCHECK(offset < kInvalidLocalOffsetInMs);
180 return static_cast<int>(offset);
184 // The implementation relies on the fact that no time zones have
185 // more than one daylight savings offset change per 19 days.
186 // In Egypt in 2010 they decided to suspend DST during Ramadan. This
187 // led to a short interval where DST is in effect from September 10 to
189 static const int kDefaultDSTDeltaInSec = 19 * kSecPerDay;
191 // Size of the Daylight Savings Time cache.
192 static const int kDSTSize = 32;
194 // Daylight Savings Time segment stores a segment of time where
195 // daylight savings offset does not change.
203 // Computes the daylight savings offset for the given time.
204 // ECMA 262 - 15.9.1.8
205 int DaylightSavingsOffsetInMs(int64_t time_ms);
207 // Sets the before_ and the after_ segments from the DST cache such that
208 // the before_ segment starts earlier than the given time and
209 // the after_ segment start later than the given time.
210 // Both segments might be invalid.
211 // The last_used counters of the before_ and after_ are updated.
212 void ProbeDST(int time_sec);
214 // Finds the least recently used segment from the DST cache that is not
215 // equal to the given 'skip' segment.
216 DST* LeastRecentlyUsedDST(DST* skip);
218 // Extends the after_ segment with the given point or resets it
219 // if it starts later than the given time + kDefaultDSTDeltaInSec.
220 inline void ExtendTheAfterSegment(int time_sec, int offset_ms);
222 // Makes the given segment invalid.
223 inline void ClearSegment(DST* segment);
225 bool InvalidSegment(DST* segment) {
226 return segment->start_sec > segment->end_sec;
231 // Daylight Saving Time cache.
233 int dst_usage_counter_;
237 int local_offset_ms_;
239 // Year/Month/Day cache.
246 base::TimezoneCache* tz_cache_;
249 } } // namespace v8::internal