Convert Linux internal time format to Windows 1601 epoch.

base/time_mac.cc

 // Copyright (c) 2008 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/time.h"
 
 #include <CoreFoundation/CFDate.h>
 #include <CoreFoundation/CFTimeZone.h>
 #include <mach/mach_time.h>
 #include <sys/time.h>
 #include <time.h>
 
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/scoped_cftyperef.h"
 
 namespace base {
 
 // The Time routines in this file use Mach and CoreFoundation APIs, since the
 // POSIX definition of time_t in Mac OS X wraps around after 2038--and
 // there are already cookie expiration dates, etc., past that time out in
 // the field.  Using CFDate prevents that problem, and using mach_absolute_time
 // for TimeTicks gives us nice high-resolution interval timing.
 
 // Time -----------------------------------------------------------------------
 
-// The internal representation of Time uses a 64-bit microsecond count
-// from 1970-01-01 00:00:00 UTC.  Core Foundation uses a double second count
-// since 2001-01-01 00:00:00 UTC.
+// Core Foundation uses a double second count since 2001-01-01 00:00:00 UTC.
+// The UNIX epoch is 1970-01-01 00:00:00 UTC.
+// Windows uses a Gregorian epoch of 1601.  We need to match this internally
+// so that our time representations match across all platforms.  See bug 14734.
+//   irb(main):010:0> Time.at(0).getutc()
+//   => Thu Jan 01 00:00:00 UTC 1970
+//   irb(main):011:0> Time.at(-11644473600).getutc()
+//   => Mon Jan 01 00:00:00 UTC 1601
+static const int64 kWindowsEpochDeltaSeconds = GG_INT64_C(11644473600);
+static const int64 kWindowsEpochDeltaMilliseconds =
+    kWindowsEpochDeltaSeconds * Time::kMillisecondsPerSecond;
+static const int64 kWindowsEpochDeltaMicroseconds =
+    kWindowsEpochDeltaSeconds * Time::kMicrosecondsPerSecond;
 
-// Some functions in time.cc use time_t directly, so we provide a zero offset
-// for them.  The epoch is 1970-01-01 00:00:00 UTC.
+// Some functions in time.cc use time_t directly, so we provide an offset
+// to convert from time_t (Unix epoch) and internal (Windows epoch).
 // static
-const int64 Time::kTimeTToMicrosecondsOffset = GG_INT64_C(0);
-
+const int64 Time::kTimeTToMicrosecondsOffset = kWindowsEpochDeltaMicroseconds;
+  
 // static
 Time Time::Now() {
   CFAbsoluteTime now =
       CFAbsoluteTimeGetCurrent() + kCFAbsoluteTimeIntervalSince1970;
-  return Time(static_cast<int64>(now * kMicrosecondsPerSecond));
+  return Time(static_cast<int64>(now * kMicrosecondsPerSecond) +
+      kWindowsEpochDeltaMicroseconds);
 }
 
 // static
 Time Time::NowFromSystemTime() {
   // Just use Now() because Now() returns the system time.
   return Now();
 }
 
 // static
 Time Time::FromExploded(bool is_local, const Exploded& exploded) {
   CFGregorianDate date;
   date.second = exploded.second +
       exploded.millisecond / static_cast<double>(kMillisecondsPerSecond);
   date.minute = exploded.minute;
   date.hour = exploded.hour;
   date.day = exploded.day_of_month;
   date.month = exploded.month;
   date.year = exploded.year;
 
   scoped_cftyperef<CFTimeZoneRef>
       time_zone(is_local ? CFTimeZoneCopySystem() : NULL);
   CFAbsoluteTime seconds = CFGregorianDateGetAbsoluteTime(date, time_zone) +
       kCFAbsoluteTimeIntervalSince1970;
-  return Time(static_cast<int64>(seconds * kMicrosecondsPerSecond));
+  return Time(static_cast<int64>(seconds * kMicrosecondsPerSecond) +
+      kWindowsEpochDeltaMicroseconds);
 }
 
 void Time::Explode(bool is_local, Exploded* exploded) const {
   CFAbsoluteTime seconds =
-      (static_cast<double>(us_) / kMicrosecondsPerSecond) -
-      kCFAbsoluteTimeIntervalSince1970;
+      (static_cast<double>((us_ - kWindowsEpochDeltaMicroseconds) /
+      kMicrosecondsPerSecond) - kCFAbsoluteTimeIntervalSince1970);
 
   scoped_cftyperef<CFTimeZoneRef>
       time_zone(is_local ? CFTimeZoneCopySystem() : NULL);
   CFGregorianDate date = CFAbsoluteTimeGetGregorianDate(seconds, time_zone);
 
   exploded->year = date.year;
   exploded->month = date.month;
   exploded->day_of_month = date.day;
   exploded->hour = date.hour;
   exploded->minute = date.minute;
@@ skipping 35 matching lines @@
 
   return TimeTicks(absolute_micro);
 }
 
 // static
 TimeTicks TimeTicks::HighResNow() {
   return Now();
 }
 
 }  // namespace base