Stopwatch class from .net 2.0 framework ported .net 1.1

/// <summary>Provides a set of methods and properties that you can use to accurately measure elapsed time.</summary>
public class Stopwatch
{
    #region SafeNativeMethods
    [DllImport("kernel32.dll")]
    private static extern bool QueryPerformanceFrequency(out long lpFrequency);
    [DllImport("kernel32.dll")]
    private static extern bool QueryPerformanceCounter(out long lpPerformanceCount);
    #endregion //SafeNativeMethods
    #region Public Fields        
    /// <summary>Gets the frequency of the timer as the number of ticks per second. This field is read-only.</summary>
    public static readonly long Frequency;
    
    /// <summary>Indicates whether the timer is based on a high-resolution performance counter. This field is read-only.</summary>
    public static readonly bool IsHighResolution;
    
    #endregion //Public Fields
    
    #region Private Fields
    private long elapsed;        
    private bool isRunning;
    private long startTimeStamp;
    
    private static readonly double tickFrequency;
    #endregion //Private Fields
    #region Constructors
    static Stopwatch()
    {
        if (!QueryPerformanceFrequency(out Stopwatch.Frequency))
        {
            Stopwatch.IsHighResolution = false;
            Stopwatch.Frequency = TimeSpan.TicksPerSecond;
            Stopwatch.tickFrequency = 1;
        }
        else
        {
            Stopwatch.IsHighResolution = true;
            Stopwatch.tickFrequency = TimeSpan.TicksPerSecond;
            Stopwatch.tickFrequency /= ((double)Stopwatch.Frequency);
        }
    }
    
    /// <summary>Initializes a new instance of the Stopwatch class.</summary>
    public Stopwatch()
    {
        this.Reset();
    }
    #endregion //Constructors
    
    #region Private Methods
    private long GetElapsedDateTimeTicks()
    {
        long ticks = this.GetRawElapsedTicks();
        if (Stopwatch.IsHighResolution)
        {
            double highTicks = ticks;
            highTicks *= Stopwatch.tickFrequency;
            return (long)highTicks;
        }
        return ticks;
    }
    private long GetRawElapsedTicks()        
    {
        long elapsedTimestamp = this.elapsed;
        if (this.isRunning)
        {
            long currentTimestamp = Stopwatch.GetTimestamp();
            long endTimestamp = currentTimestamp - this.startTimeStamp;
            elapsedTimestamp += endTimestamp;
        }
        return elapsedTimestamp;
    }
    #endregion //Private Methods
    #region Public Methods
    /// <summary>Gets the current number of ticks in the timer mechanism.</summary>
    /// <returns>A long integer representing the tick counter value of the underlying timer mechanism.</returns>
    public static long GetTimestamp()        
    {
        if (Stopwatch.IsHighResolution)
        {
            long ticks = 0;
            QueryPerformanceCounter(out ticks);
            return ticks;
        }
        return DateTime.UtcNow.Ticks;
    }
    /// <summary>Stops time interval measurement and resets the elapsed time to zero.</summary>
    public void Reset()        
    {
        this.elapsed = 0;
        this.isRunning = false;
        this.startTimeStamp = 0;
    }
    /// <summary>Starts, or resumes, measuring elapsed time for an interval.</summary>
    public void Start()        
    {
        if (!this.isRunning)
        {
            this.startTimeStamp = Stopwatch.GetTimestamp();
            this.isRunning = true;
        }
    }
    /// <summary>Initializes a new Stopwatch instance, sets the elapsed time property to zero, and starts measuring elapsed time.</summary>
    /// <returns>A Stopwatch that has just begun measuring elapsed time.</returns>
    public static Stopwatch StartNew()        
    {
        Stopwatch stopwatch = new Stopwatch();
        stopwatch.Start();
        return stopwatch;
    }
    /// <summary>Stops measuring elapsed time for an interval.</summary>
    public void Stop()        
    {
        if (this.isRunning)
        {
            long currentTimestamp = Stopwatch.GetTimestamp();
            long endTimestamp = currentTimestamp - this.startTimeStamp;
            this.elapsed += endTimestamp;
            this.isRunning = false;
        }
    }
    #endregion //Public Methods
    
    #region Public Properties
    /// <summary>Gets the total elapsed time measured by the current instance.</summary>
    /// <value>A read-only System.TimeSpan representing the total elapsed time measured by the current instance.</value>
    public TimeSpan Elapsed
    {
        get { return new TimeSpan(this.GetElapsedDateTimeTicks()); }
    }
    
    /// <summary>Gets the total elapsed time measured by the current instance, in milliseconds.</summary>
    public long ElapsedMilliseconds
    {
        get { return (this.GetElapsedDateTimeTicks() / TimeSpan.TicksPerMillisecond); }
    }
    /// <summary>Gets the total elapsed time measured by the current instance, in timer ticks.</summary>
    public long ElapsedTicks
    {
        get { return this.GetRawElapsedTicks(); }
    }
    
    /// <summary>Gets a value indicating whether the Stopwatch timer is running.</summary>
    public bool IsRunning
    {
        get { return this.isRunning; }
    }
    #endregion //Public Properties
}