Add support for timezone offset and timezone name.

runtime/vm/os_win.cc

Index: runtime/vm/os_win.cc
diff --git a/runtime/vm/os_win.cc b/runtime/vm/os_win.cc
index 96a00359df610e396aefefd1da4776a427c61a2d..37817cfd80dc0d3a57d38601e7786c83981aad69 100644
--- a/runtime/vm/os_win.cc
+++ b/runtime/vm/os_win.cc
@@ -54,6 +54,61 @@ bool OS::MkTime(tm* tm, int64_t* seconds_result) {
 }
 
 
+// Calls _tzset if necessary.
+static void TzSet() {
+  static bool tz_is_initialized = false;
+  if (!tz_is_initialized) {
+    _tzset();
+    tz_is_initialized = true;
+  }
+}
+
+
+int GetDaylightSavingOffsetInSeconds() {

[Mads Ager (google), 2012/05/21 12:53:28]

static int GetDaylightSavingsOffsetInSeconds() {

[floitsch, 2012/05/21 13:26:45]

Done.

+  TzSet();

[Mads Ager (google), 2012/05/21 12:53:28]

Is the call to TzSet needed here?

[floitsch, 2012/05/21 13:26:45]

No. Apparently not. Removed.

+  TIME_ZONE_INFORMATION zone_information;
+  memset(&zone_information, 0, sizeof(zone_information));
+  if (GetTimeZoneInformation(&zone_information) == TIME_ZONE_ID_INVALID) {
+    // By default the daylight saving offset is an hour.
+    return -60 * 60;
+  } else {
+    return static_cast<int>(zone_information.DaylightBias * 60);
+  }
+}
+
+bool OS::GetTimeZoneName(int64_t seconds_since_epoch,

[Mads Ager (google), 2012/05/21 12:53:28]

There is a TzSet() call missing in this method I think. Using _tzname without
calling _tzset?

[floitsch, 2012/05/21 13:26:45]

Updated comment: LocalTime implicitly calls tzset.

Therefore could also remove TzSet in GetTimeZoneOffsetInSeconds, and as a
consequence the whole TzSet function.

+                         const char** name_result) {
+  tm decomposed;
+  bool succeeded = LocalTime(seconds_since_epoch, &decomposed);
+  if (!succeeded) return false;
+  int inDaylightSavingsTime = decomposed.tm_isdst;
+  if (inDaylightSavingsTime != 0 && inDaylightSavingsTime != 1) {
+    return false;
+  }
+  *name_result = _tzname[inDaylightSavingsTime];
+  return true;
+}
+
+
+bool OS::GetTimeZoneOffsetInSeconds(int64_t seconds_since_epoch,
+                                    int* offset_result) {
+  tm decomposed;
+  bool succeeded = LocalTime(seconds_since_epoch, &decomposed);
+  if (!succeeded) return false;
+  int inDaylightSavingsTime = decomposed.tm_isdst;
+  if (inDaylightSavingsTime != 0 && inDaylightSavingsTime != 1) return false;

[Mads Ager (google), 2012/05/21 12:53:28]

Either a one-liner above or split into lines with braces here as above.

[floitsch, 2012/05/21 13:26:45]

Done.

+  TzSet();
+  // Dart and Windows disagree on the sign of the bias.
+  *offset_result = static_cast<int>(-_timezone);
+  if (inDaylightSavingsTime == 1) {
+    static int daylight_offset = GetDaylightSavingOffsetInSeconds()
+    // Subtract because windows and Dart disagree on the sign.
+    *offset_result -= daylight_offset;
+  }
+  return true;
+}
+
+
 int64_t OS::GetCurrentTimeMillis() {
   return GetCurrentTimeMicros() / 1000;
 }