获取程序准确运行时间

WEB CaM DEMO的程序：

using System;

namespace Timing
{
public class Counter
{
long elapsedCount = 0;
long startCount = 0;

public void Start()
{
startCount = 0;
QueryPerformanceCounter(ref startCount);
}

public void Stop()
{
long stopCount = 0;
QueryPerformanceCounter(ref stopCount);

elapsedCount += (stopCount - startCount);
}

public void Clear()
{
elapsedCount = 0;
}

public float Seconds
{
get
{
long freq = 0;
QueryPerformanceFrequency(ref freq);
return((float) elapsedCount / (float) freq);
}
}

public override string ToString()
{
return String.Format("{0} Seconds.", Seconds);
}

static long Frequency
{
get
{
long freq = 0;
QueryPerformanceFrequency(ref freq);
return freq;
}
}
static long Value
{
get
{
long count = 0;
QueryPerformanceCounter(ref count);
return count;
}
}

[System.Runtime.InteropServices.DllImport("KERNEL32")]
private static extern bool QueryPerformanceCounter( ref long lpPerformanceCount);

[System.Runtime.InteropServices.DllImport("KERNEL32")]
private static extern bool QueryPerformanceFrequency( ref long lpFrequency);
}
}