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 int64_t ToLocal(int64_t time_ms) {
108 return time_ms + LocalOffsetInMs() + DaylightSavingsOffsetInMs(time_ms);
111 // ECMA 262 - 15.9.1.9
112 // UTC(t) = t - LocalTZA - DaylightSavingTA(t - LocalTZA)
113 int64_t ToUTC(int64_t time_ms) {
114 // We need to compute UTC time that corresponds to the given local time.
115 // Literally following spec here leads to incorrect time computation at
116 // the points were we transition to and from DST.
118 // The following shows that using DST for (t - LocalTZA - hour) produces
119 // correct conversion.
121 // Consider transition to DST at local time L1.
122 // Let L0 = L1 - hour, L2 = L1 + hour,
123 // U1 = UTC time that corresponds to L1,
125 // Transitioning to DST moves local clock one hour forward L1 => L2, so
126 // U0 = UTC time that corresponds to L0 = L0 - LocalTZA,
127 // U1 = UTC time that corresponds to L1 = L1 - LocalTZA,
128 // U1 = UTC time that corresponds to L2 = L2 - LocalTZA - hour.
129 // Note that DST(U0 - hour) = 0, DST(U0) = 0, DST(U1) = 1.
130 // U0 = L0 - LocalTZA - DST(L0 - LocalTZA - hour),
131 // U1 = L1 - LocalTZA - DST(L1 - LocalTZA - hour),
132 // U1 = L2 - LocalTZA - DST(L2 - LocalTZA - hour).
134 // Consider transition from DST at local time L1.
135 // Let L0 = L1 - hour,
136 // U1 = UTC time that corresponds to L1,
137 // U0 = U1 - hour, U2 = U1 + hour.
138 // Transitioning from DST moves local clock one hour back L1 => L0, so
139 // U0 = UTC time that corresponds to L0 (before transition)
140 // = L0 - LocalTZA - hour.
141 // U1 = UTC time that corresponds to L0 (after transition)
142 // = L0 - LocalTZA = L1 - LocalTZA - hour
143 // U2 = UTC time that corresponds to L1 = L1 - LocalTZA.
144 // Note that DST(U0) = 1, DST(U1) = 0, DST(U2) = 0.
145 // U0 = L0 - LocalTZA - DST(L0 - LocalTZA - hour) = L0 - LocalTZA - DST(U0).
146 // U2 = L1 - LocalTZA - DST(L1 - LocalTZA - hour) = L1 - LocalTZA - DST(U1).
147 // It is impossible to get U1 from local time.
149 const int kMsPerHour = 3600 * 1000;
150 time_ms -= LocalOffsetInMs();
151 return time_ms - DaylightSavingsOffsetInMs(time_ms - kMsPerHour);
155 // Computes a time equivalent to the given time according
156 // to ECMA 262 - 15.9.1.9.
157 // The issue here is that some library calls don't work right for dates
158 // that cannot be represented using a non-negative signed 32 bit integer
159 // (measured in whole seconds based on the 1970 epoch).
160 // We solve this by mapping the time to a year with same leap-year-ness
161 // and same starting day for the year. The ECMAscript specification says
162 // we must do this, but for compatibility with other browsers, we use
163 // the actual year if it is in the range 1970..2037
164 int64_t EquivalentTime(int64_t time_ms) {
165 int days = DaysFromTime(time_ms);
166 int time_within_day_ms = static_cast<int>(time_ms - days * kMsPerDay);
167 int year, month, day;
168 YearMonthDayFromDays(days, &year, &month, &day);
169 int new_days = DaysFromYearMonth(EquivalentYear(year), month) + day - 1;
170 return static_cast<int64_t>(new_days) * kMsPerDay + time_within_day_ms;
173 // Returns an equivalent year in the range [2008-2035] matching
175 // - week day of first day.
176 // ECMA 262 - 15.9.1.9.
177 int EquivalentYear(int year) {
178 int week_day = Weekday(DaysFromYearMonth(year, 0));
179 int recent_year = (IsLeap(year) ? 1956 : 1967) + (week_day * 12) % 28;
180 // Find the year in the range 2008..2037 that is equivalent mod 28.
181 // Add 3*28 to give a positive argument to the modulus operator.
182 return 2008 + (recent_year + 3 * 28 - 2008) % 28;
185 // Given the number of days since the epoch, computes
186 // the corresponding year, month, and day.
187 void YearMonthDayFromDays(int days, int* year, int* month, int* day);
189 // Computes the number of days since the epoch for
190 // the first day of the given month in the given year.
191 int DaysFromYearMonth(int year, int month);
193 // Cache stamp is used for invalidating caches in JSDate.
194 // We increment the stamp each time when the timezone information changes.
195 // JSDate objects perform stamp check and invalidate their caches if
196 // their saved stamp is not equal to the current stamp.
197 Smi* stamp() { return stamp_; }
198 void* stamp_address() { return &stamp_; }
200 // These functions are virtual so that we can override them when testing.
201 virtual int GetDaylightSavingsOffsetFromOS(int64_t time_sec) {
202 double time_ms = static_cast<double>(time_sec * 1000);
203 return static_cast<int>(
204 base::OS::DaylightSavingsOffset(time_ms, tz_cache_));
207 virtual int GetLocalOffsetFromOS() {
208 double offset = base::OS::LocalTimeOffset(tz_cache_);
209 DCHECK(offset < kInvalidLocalOffsetInMs);
210 return static_cast<int>(offset);
214 // The implementation relies on the fact that no time zones have
215 // more than one daylight savings offset change per 19 days.
216 // In Egypt in 2010 they decided to suspend DST during Ramadan. This
217 // led to a short interval where DST is in effect from September 10 to
219 static const int kDefaultDSTDeltaInSec = 19 * kSecPerDay;
221 // Size of the Daylight Savings Time cache.
222 static const int kDSTSize = 32;
224 // Daylight Savings Time segment stores a segment of time where
225 // daylight savings offset does not change.
233 // Computes the daylight savings offset for the given time.
234 // ECMA 262 - 15.9.1.8
235 int DaylightSavingsOffsetInMs(int64_t time_ms);
237 // Sets the before_ and the after_ segments from the DST cache such that
238 // the before_ segment starts earlier than the given time and
239 // the after_ segment start later than the given time.
240 // Both segments might be invalid.
241 // The last_used counters of the before_ and after_ are updated.
242 void ProbeDST(int time_sec);
244 // Finds the least recently used segment from the DST cache that is not
245 // equal to the given 'skip' segment.
246 DST* LeastRecentlyUsedDST(DST* skip);
248 // Extends the after_ segment with the given point or resets it
249 // if it starts later than the given time + kDefaultDSTDeltaInSec.
250 inline void ExtendTheAfterSegment(int time_sec, int offset_ms);
252 // Makes the given segment invalid.
253 inline void ClearSegment(DST* segment);
255 bool InvalidSegment(DST* segment) {
256 return segment->start_sec > segment->end_sec;
261 // Daylight Saving Time cache.
263 int dst_usage_counter_;
267 int local_offset_ms_;
269 // Year/Month/Day cache.
276 base::TimezoneCache* tz_cache_;
279 } // namespace internal