getting the TIMEZONE information

1. take one dropdownlist
2.one button
3.one multiline textbox

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using Microsoft.Win32;
using System.Runtime.InteropServices;
using System.Text;

namespace TimeZoneApp
{
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{

}

public struct SYSTEMDATETIME
{
public short syear;
public short smonth;
public short sdayofweek;
public short day;
public short hour;
public short min;
public short sec;
public short millisec;
}
public struct TimezoneBias
{
public Int32 _bias;
public Int32 _standardbias;
public Int32 _daylightbias;
public SYSTEMDATETIME _standarddate;
public SYSTEMDATETIME _daylightdate;
}
public struct TimeZoneInformation
{
private string _keyname;

public string Keyname
{
get { return _keyname; }
set { _keyname = value; }
}

private string _standardname;

public string Standardname
{
get { return _standardname; }
set { _standardname = value; }
}
private string _daylightname;

public string Daylightname
{
get { return _daylightname; }
set { _daylightname = value; }
}

private TimezoneBias _timeZoneBias;

public TimezoneBias TimeZoneBias
{
get { return _timeZoneBias; }
set { _timeZoneBias = value; }
}

private string _displaystring;

public string Displaystring
{
get { return _displaystring; }
set { _displaystring = value; }
}
}
public class TimeZoneComparison : IComparer<TimeZoneInformation>
{
public int Compare(TimeZoneInformation TZI1, TimeZoneInformation TZI2)
{
if (TZI1.TimeZoneBias._bias > TZI2.TimeZoneBias._bias)
return -1;
else if (TZI1.TimeZoneBias._bias < TZI2.TimeZoneBias._bias)
return 1;
else
return 0;
}
}
protected void TimeZone_Click(object sender, EventArgs e)
{

RegistryKey Reg = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones");
List<TimeZoneInformation> arr = new List<TimeZoneInformation>();

foreach (string SubKey in Reg.GetSubKeyNames())
{
RegistryKey KeyValue = Reg.OpenSubKey(SubKey);
TimeZoneInformation TZI = new TimeZoneInformation();
TZI.Keyname = SubKey.ToString();
TZI.Standardname = KeyValue.GetValue("Std").ToString();
TZI.Daylightname = KeyValue.GetValue("Dlt").ToString();
TZI.Displaystring = KeyValue.GetValue("Display").ToString();
TZI.TimeZoneBias = new TimezoneBias();

Byte[] b = (byte[])KeyValue.GetValue("TZI");
IntPtr buffer = Marshal.AllocHGlobal(Marshal.SizeOf(TZI.TimeZoneBias));
Marshal.Copy(b, 0, buffer, 44);
TZI.TimeZoneBias = (TimezoneBias)Marshal.PtrToStructure(buffer, typeof(TimezoneBias));
arr.Add(TZI);
}
TimeZoneComparison TZC = new TimeZoneComparison();
arr.Sort(TZC);
DropDownList1.DataTextField = "Displaystring";
DropDownList1.DataValueField = "Keyname";
DropDownList1.DataSource = arr;
DropDownList1.DataBind();
}

public DateTime GetAdjustedDate(DateTime dt,int day)
{
DateTime monthenddate = dt.AddMonths(1).AddDays(-1);
if (dt.DayOfWeek != DayOfWeek.Sunday)
dt = dt.AddDays(7 - (Int32)dt.DayOfWeek);
if (monthenddate.DayOfWeek != DayOfWeek.Sunday)
monthenddate = monthenddate.AddDays((-1) * (Int32)monthenddate.DayOfWeek);

switch (day)
{
case 1:
return dt;
case 2:
return dt.AddDays(7);
case 3:
return dt.AddDays(14);
case 4:
return dt.AddDays(21);
case 5:
return monthenddate;
default:
return dt;
}
}
protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
RegistryKey Reg = Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones");
RegistryKey KeyValue = Reg.OpenSubKey(DropDownList1.SelectedItem.Value);
TimeZoneInformation TZI = new TimeZoneInformation();
String daylightdatestring,daylightsavingenddate;
TZI.Displaystring = KeyValue.GetValue("Display").ToString();
Byte[] b = (byte[])KeyValue.GetValue("TZI");

IntPtr buffer = Marshal.AllocHGlobal(Marshal.SizeOf(TZI.TimeZoneBias));
Marshal.Copy(b,0,buffer,44);
TZI.TimeZoneBias = (TimezoneBias)Marshal.PtrToStructure(buffer, typeof(TimezoneBias));
if (TZI.TimeZoneBias._daylightdate.smonth > 0)
{
DateTime dt = new DateTime(DateTime.Now.Year, TZI.TimeZoneBias._daylightdate.smonth, 1, TZI.TimeZoneBias._daylightdate.hour, TZI.TimeZoneBias._daylightdate.min,TZI.TimeZoneBias._daylightdate.sec, TZI.TimeZoneBias._daylightdate.millisec);
dt = GetAdjustedDate(dt, TZI.TimeZoneBias._daylightdate.day);
daylightdatestring = dt.ToString();
}
else
{
daylightdatestring = "No Daylight Saving Experienced in this region ";
}

StringBuilder str = new StringBuilder();
str.Append("Time Zone Name Selected : " + TZI.Displaystring + "\n\r");
str.Append("Time Zone Bias From GMT : " + TZI.TimeZoneBias._bias + "\n\r");
str.Append("DayLight Saving starts from : " + daylightdatestring + "\n\r");
SummaryBox.Text = str.ToString();
}
}
}