.Net CF下精确的计时器

.Net CF下精确的计时器
用法：
Dim t as New AtomicCF.Timer
t.start()
....'Some functions here
Dim TimeLapsed as Long = t.stop()

Imports  System.Runtime.InteropServices
Namespace AtomicCF Namespace AtomicCF

    Public Class TimerClass Timer
        <DllImport("coredll.dll", EntryPoint:="QueryPerformanceCounter")> _
        Public Shared Function QueryPerformanceCounter()Function QueryPerformanceCounter(ByRef perfCounter As Long) As Integer
        End Function

        <DllImport("coredll.dll", EntryPoint:="QueryPerformanceFrequency")> _
        Public Shared Function QueryPerformanceFrequency()Function QueryPerformanceFrequency(ByRef frequency As Long) As Integer
        End Function

        Private m_frequency As Int64
        Private m_start As Int64

        Public Sub New()Sub New()
            If QueryPerformanceFrequency(m_frequency) = 0 Then
                Throw New ApplicationException
            End If
            'Convert to ms.
            m_frequency = CLng(m_frequency / 1000)
        End Sub

        Public Sub Start()Sub Start()
            If QueryPerformanceCounter(m_start) = 0 Then
                Throw New ApplicationException
            End If
        End Sub

        Public Function [()Function [Stop]() As Int64            Dim lStop As Int64 = 0            If QueryPerformanceCounter(lStop) = 0 Then                Throw New ApplicationException            End If            Return CLng((lStop - m_start) / m_frequency)        End Function    End ClassEnd Namespace Namespace