[vbnet]

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بالنسبة لـ CRC32

منقول

هذا كلاس CrcStream

كود :

Imports System.IO

''' <summary>
''' Encapsulates a <see cref="System.IO.Stream" /> to calculate the CRC32 checksum on-the-fly as data passes through.
''' </summary>
Public Class CrcStream
    Inherits Stream
    ''' <summary>
    ''' Encapsulate a <see cref="System.IO.Stream" />.
    ''' </summary>
    ''' <param name="stream">The stream to calculate the checksum for.</param>
    Public Sub New(ByVal stream As Stream)
        Me.m_stream = stream
    End Sub

    Private m_stream As Stream

    ''' <summary>
    ''' Gets the underlying stream.
    ''' </summary>
    Public ReadOnly Property Stream() As Stream
        Get
            Return m_stream
        End Get
    End Property

    Public Overrides ReadOnly Property CanRead() As Boolean
        Get
            Return m_stream.CanRead
        End Get
    End Property

    Public Overrides ReadOnly Property CanSeek() As Boolean
        Get
            Return m_stream.CanSeek
        End Get
    End Property

    Public Overrides ReadOnly Property CanWrite() As Boolean
        Get
            Return m_stream.CanWrite
        End Get
    End Property

    Public Overrides Sub Flush()
        m_stream.Flush()
    End Sub

    Public Overrides ReadOnly Property Length() As Long
        Get
            Return m_stream.Length
        End Get
    End Property

    Public Overrides Property Position() As Long
        Get
            Return m_stream.Position
        End Get
        Set(ByVal value As Long)
            m_stream.Position = value
        End Set
    End Property

    Public Overrides Function Seek(ByVal offset As Long, ByVal origin As SeekOrigin) As Long
        Return m_stream.Seek(offset, origin)
    End Function

    Public Overrides Sub SetLength(ByVal value As Long)
        m_stream.SetLength(value)
    End Sub

    Public Overrides Function Read(ByVal buffer As Byte(), ByVal offset As Integer, ByVal count As Integer) As Integer
        count = m_stream.Read(buffer, offset, count)
        m_readCrc = CalculateCrc(m_readCrc, buffer, offset, count)
        Return count
    End Function

    Public Overrides Sub Write(ByVal buffer As Byte(), ByVal offset As Integer, ByVal count As Integer)
        m_stream.Write(buffer, offset, count)

        m_writeCrc = CalculateCrc(m_writeCrc, buffer, offset, count)
    End Sub

    Private Function CalculateCrc(ByVal crc As UInteger, ByVal buffer As Byte(), ByVal offset As Integer, ByVal count As Integer) As UInteger
        Dim i As Integer = offset, [end] As Integer = offset + count
        While i < [end]
            crc = (crc >> 8) Xor table((crc Xor buffer(i)) And &HFF)
            i += 1
        End While

        Return crc
    End Function

    Private Shared table As UInteger() = GenerateTable()

    Private Shared Function GenerateTable() As UInteger()
        Dim table As UInteger() = New UInteger(255) {}

        Dim crc As UInteger
        Const poly As UInteger = &HEDB88320UI
        For i As UInteger = 0 To table.Length - 1
            crc = i
            For j As Integer = 8 To 1 Step -1
                If (crc And 1) = 1 Then
                    crc = (crc >> 1) Xor poly
                Else
                    crc >>= 1
                End If
            Next
            table(i) = crc
        Next

        Return table


    End Function

    Private m_readCrc As UInteger = &HFFFFFFFFUI

    ''' <summary>
    ''' Gets the CRC checksum of the data that was read by the stream thus far.
    ''' </summary>
    Public ReadOnly Property ReadCrc() As UInteger
        Get
            Return m_readCrc Xor &HFFFFFFFFUI
        End Get
    End Property

    Private m_writeCrc As UInteger = &HFFFFFFFFUI

    ''' <summary>
    ''' Gets the CRC checksum of the data that was written to the stream thus far.
    ''' </summary>
    Public ReadOnly Property WriteCrc() As UInteger
        Get
            Return m_writeCrc Xor &HFFFFFFFFUI
        End Get
    End Property

    ''' <summary>
    ''' Resets the read and write checksums.
    ''' </summary>
    Public Sub ResetChecksum()
        m_readCrc = &HFFFFFFFFUI
        m_writeCrc = &HFFFFFFFFUI
    End Sub

End Class

طريقة استخدامه

كود :

Public Class Form1

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        'Open a file stream, encapsulate it in CrcStream
        Dim file As New IO.FileStream("C:\test.exe", IO.FileMode.Open)
        Dim stream As New CrcStream(file)

        'Use the file somehow -- in this case, read it as a string
        Dim reader As New IO.StreamReader(stream)
        Dim text As String = reader.ReadToEnd()

        'Print the checksum
        MessageBox.Show("CRC: " & stream.ReadCrc.ToString("X8"))

    End Sub

End Class

المصدر (CrcStream stream checksum calculator)