253 lines
11 KiB
C#
253 lines
11 KiB
C#
// ==++==
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//
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// Copyright (c) Microsoft Corporation. All rights reserved.
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//
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// ==--==
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/*============================================================
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**
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** Class: TimeZone
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**
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**
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** Purpose:
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** This class is used to represent a TimeZone. It
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** has methods for converting a DateTime to UTC from local time
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** and to local time from UTC and methods for getting the
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** standard name and daylight name of the time zone.
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**
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** The only TimeZone that we support in version 1 is the
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** CurrentTimeZone as determined by the system timezone.
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**
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**
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============================================================*/
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#if !FEATURE_CORECLR
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namespace System {
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using System;
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using System.Text;
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using System.Threading;
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using System.Collections;
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using System.Globalization;
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[Serializable]
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[System.Runtime.InteropServices.ComVisible(true)]
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#if FEATURE_CORECLR
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[Obsolete("System.TimeZone has been deprecated. Please investigate the use of System.TimeZoneInfo instead.")]
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#endif
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public abstract class TimeZone {
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private static volatile TimeZone currentTimeZone = null;
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// Private object for locking instead of locking on a public type for SQL reliability work.
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private static Object s_InternalSyncObject;
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private static Object InternalSyncObject {
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get {
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if (s_InternalSyncObject == null) {
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Object o = new Object();
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Interlocked.CompareExchange<Object>(ref s_InternalSyncObject, o, null);
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}
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return s_InternalSyncObject;
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}
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}
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protected TimeZone() {
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}
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public static TimeZone CurrentTimeZone {
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get {
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//Grabbing the cached value is required at the top of this function so that
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//we don't incur a race condition with the ResetTimeZone method below.
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TimeZone tz = currentTimeZone;
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if (tz == null) {
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lock(InternalSyncObject) {
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if (currentTimeZone == null) {
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currentTimeZone = new CurrentSystemTimeZone();
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}
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tz = currentTimeZone;
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}
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}
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return (tz);
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}
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}
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//This method is called by CultureInfo.ClearCachedData in response to control panel
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//change events. It must be synchronized because otherwise there is a race condition
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//with the CurrentTimeZone property above.
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internal static void ResetTimeZone() {
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if (currentTimeZone!=null) {
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lock(InternalSyncObject) {
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currentTimeZone = null;
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}
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}
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}
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public abstract String StandardName {
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get;
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}
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public abstract String DaylightName {
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get;
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}
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public abstract TimeSpan GetUtcOffset(DateTime time);
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//
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// Converts the specified datatime to the Universal time base on the current timezone
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//
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public virtual DateTime ToUniversalTime(DateTime time) {
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if (time.Kind == DateTimeKind.Utc) {
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return time;
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}
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long tickCount = time.Ticks - GetUtcOffset(time).Ticks;
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if (tickCount>DateTime.MaxTicks) {
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return new DateTime(DateTime.MaxTicks, DateTimeKind.Utc);
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}
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if (tickCount<DateTime.MinTicks) {
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return new DateTime(DateTime.MinTicks, DateTimeKind.Utc);
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}
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return new DateTime(tickCount, DateTimeKind.Utc);
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}
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//
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// Convert the specified datetime value from UTC to the local time based on the time zone.
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//
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public virtual DateTime ToLocalTime(DateTime time) {
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if (time.Kind == DateTimeKind.Local) {
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return time;
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}
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Boolean isAmbiguousLocalDst = false;
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Int64 offset = ((CurrentSystemTimeZone)(TimeZone.CurrentTimeZone)).GetUtcOffsetFromUniversalTime(time, ref isAmbiguousLocalDst);
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return new DateTime(time.Ticks + offset, DateTimeKind.Local, isAmbiguousLocalDst);
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}
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// Return an array of DaylightTime which reflects the daylight saving periods in a particular year.
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// We currently only support having one DaylightSavingTime per year.
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// If daylight saving time is not used in this timezone, null will be returned.
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public abstract DaylightTime GetDaylightChanges(int year);
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public virtual bool IsDaylightSavingTime(DateTime time) {
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return (IsDaylightSavingTime(time, GetDaylightChanges(time.Year)));
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}
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// Check if the specified time is in a daylight saving time. Allows the user to
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// specify the array of Daylight Saving Times.
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public static bool IsDaylightSavingTime(DateTime time, DaylightTime daylightTimes) {
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return CalculateUtcOffset(time, daylightTimes)!=TimeSpan.Zero;
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}
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//
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// NOTENOTE: Implementation detail
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// In the transition from standard time to daylight saving time,
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// if we convert local time to Universal time, we can have the
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// following (take PST as an example):
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// Local Universal UTC Offset
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// ----- --------- ----------
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// 01:00AM 09:00 -8:00
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// 02:00 (=> 03:00) 10:00 -8:00 [This time doesn't actually exist, but it can be created from DateTime]
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// 03:00 10:00 -7:00
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// 04:00 11:00 -7:00
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// 05:00 12:00 -7:00
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//
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// So from 02:00 - 02:59:59, we should return the standard offset, instead of the daylight saving offset.
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//
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// In the transition from daylight saving time to standard time,
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// if we convert local time to Universal time, we can have the
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// following (take PST as an example):
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// Local Universal UTC Offset
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// ----- --------- ----------
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// 01:00AM 08:00 -7:00
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// 02:00 (=> 01:00) 09:00 -8:00
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// 02:00 10:00 -8:00
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// 03:00 11:00 -8:00
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// 04:00 12:00 -8:00
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//
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// So in this case, the 02:00 does exist after the first 2:00 rolls back to 01:00. We don't need to special case this.
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// But note that there are two 01:00 in the local time.
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//
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// And imagine if the daylight saving offset is negative (although this does not exist in real life)
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// In the transition from standard time to daylight saving time,
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// if we convert local time to Universal time, we can have the
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// following (take PST as an example, but the daylight saving offset is -01:00):
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// Local Universal UTC Offset
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// ----- --------- ----------
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// 01:00AM 09:00 -8:00
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// 02:00 (=> 01:00) 10:00 -9:00
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// 02:00 11:00 -9:00
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// 03:00 12:00 -9:00
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// 04:00 13:00 -9:00
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// 05:00 14:00 -9:00
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//
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// So in this case, the 02:00 does exist after the first 2:00 rolls back to 01:00. We don't need to special case this.
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//
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// In the transition from daylight saving time to standard time,
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// if we convert local time to Universal time, we can have the
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// following (take PST as an example, daylight saving offset is -01:00):
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//
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// Local Universal UTC Offset
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// ----- --------- ----------
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// 01:00AM 10:00 -9:00
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// 02:00 (=> 03:00) 11:00 -9:00
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// 03:00 11:00 -8:00
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// 04:00 12:00 -8:00
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// 05:00 13:00 -8:00
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// 06:00 14:00 -8:00
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//
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// So from 02:00 - 02:59:59, we should return the daylight saving offset, instead of the standard offset.
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//
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internal static TimeSpan CalculateUtcOffset(DateTime time, DaylightTime daylightTimes) {
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if (daylightTimes==null) {
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return TimeSpan.Zero;
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}
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DateTimeKind kind = time.Kind;
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if (kind == DateTimeKind.Utc) {
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return TimeSpan.Zero;
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}
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DateTime startTime;
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DateTime endTime;
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// startTime and endTime represent the period from either the start of DST to the end and includes the
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// potentially overlapped times
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startTime = daylightTimes.Start + daylightTimes.Delta;
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endTime = daylightTimes.End;
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// For normal time zones, the ambiguous hour is the last hour of daylight saving when you wind the
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// clock back. It is theoretically possible to have a positive delta, (which would really be daylight
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// reduction time), where you would have to wind the clock back in the begnning.
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DateTime ambiguousStart;
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DateTime ambiguousEnd;
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if (daylightTimes.Delta.Ticks > 0) {
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ambiguousStart = endTime - daylightTimes.Delta;
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ambiguousEnd = endTime;
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} else {
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ambiguousStart = startTime;
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ambiguousEnd = startTime - daylightTimes.Delta;
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}
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Boolean isDst = false;
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if (startTime > endTime) {
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// In southern hemisphere, the daylight saving time starts later in the year, and ends in the beginning of next year.
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// Note, the summer in the southern hemisphere begins late in the year.
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if (time >= startTime || time < endTime) {
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isDst = true;
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}
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}
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else if (time>=startTime && time < endTime) {
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// In northern hemisphere, the daylight saving time starts in the middle of the year.
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isDst = true;
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}
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// If this date was previously converted from a UTC date and we were able to detect that the local
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// DateTime would be ambiguous, this data is stored in the DateTime to resolve this ambiguity.
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if (isDst && time >= ambiguousStart && time < ambiguousEnd) {
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isDst = time.IsAmbiguousDaylightSavingTime();
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}
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if (isDst) {
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return daylightTimes.Delta;
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}
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return TimeSpan.Zero;
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}
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}
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}
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#endif // FEATURE_CORECLR
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