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以下が改良したコードです。
Namespace Force_Crc32
Friend Class SafeProxy
Private Const Poly As UInteger = &HEDB88320UI
Private Shared ReadOnly _table As UInteger() = New UInteger(16 * 256 - 1) {}
Shared Sub New()
For i As UInteger = 0 To 255
Dim res As UInteger = i
For t As Integer = 0 To 15
For k As Integer = 0 To 7
res = If((res And 1) = 1, Poly Xor (res >> 1), (res >> 1))
Next
_table((t * 256) + i) = res
Next
Next
End Sub
Public Function Append(ByVal crc As UInteger, ByVal input As Byte(), ByVal offset As Integer, ByVal length As Integer) As UInteger
Dim crcLocal As UInteger = UInteger.MaxValue Xor crc
Dim table As UInteger() = _table
While length >= 16
crcLocal = table((15 * 256) + ((crcLocal Xor input(offset)) And &HFF)) _
Xor table((14 * 256) + (((crcLocal >> 8) Xor input(offset + 1)) And &HFF)) _
Xor table((13 * 256) + (((crcLocal >> 16) Xor input(offset + 2)) And &HFF)) _
Xor table((12 * 256) + (((crcLocal >> 24) Xor input(offset + 3)) And &HFF)) _
Xor table((11 * 256) + input(offset + 4)) _
Xor table((10 * 256) + input(offset + 5)) _
Xor table((9 * 256) + input(offset + 6)) _
Xor table((8 * 256) + input(offset + 7)) _
Xor table((7 * 256) + input(offset + 8)) _
Xor table((6 * 256) + input(offset + 9)) _
Xor table((5 * 256) + input(offset + 10)) _
Xor table((4 * 256) + input(offset + 11)) _
Xor table((3 * 256) + input(offset + 12)) _
Xor table((2 * 256) + input(offset + 13)) _
Xor table((1 * 256) + input(offset + 14)) _
Xor table((0 * 256) + input(offset + 15))
offset += 16
length -= 16
End While
'While System.Threading.Interlocked.Decrement(length) >= 0
While length >= 0
length -= 1
'crcLocal = table((crcLocal Xor input(System.Math.Max(System.Threading.Interlocked.Increment(offset), offset - 1))) And &HFF) Xor crcLocal >> 8
offset += 1
crcLocal = table((crcLocal Xor input(offset)) And &HFF) Xor crcLocal >> 8
End While
Return crcLocal Xor UInteger.MaxValue
End Function
End Class
End Namespace
Imports System
Imports System.Security.Cryptography
Namespace Force_Crc32
''' <summary>
''' Implementation of CRC-32.
''' This class supports several convenient static methods returning the CRC as UInt32.
''' </summary>
Public Class Crc32Algorithm
Inherits HashAlgorithm
Private _currentCrc As UInteger
''' <summary>
''' Initializes a new instance of the <see cref="Crc32Algorithm"/> class.
''' </summary>
Public Sub New()
#If Not NETCORE Then
HashSizeValue = 32
#End If
End Sub
''' <summary>
''' Computes CRC-32 from multiple buffers.
''' Call this method multiple times to chain multiple buffers.
''' </summary>
''' <param name="initial">
''' Initial CRC value for the algorithm. It is zero for the first buffer.
''' Subsequent buffers should have their initial value set to CRC value returned by previous call to this method.
''' </param>
''' <param name="input">Input buffer with data to be checksummed.</param>
''' <param name="offset">Offset of the input data within the buffer.</param>
''' <param name="length">Length of the input data in the buffer.</param>
''' <returns>Accumulated CRC-32 of all buffers processed so far.</returns>
Public Shared Function Append(ByVal initial As UInteger, ByVal input2 As Byte(), ByVal offset As Integer, ByVal length As Integer) As UInteger
If input2 Is Nothing Then
Throw New ArgumentNullException()
End If
If offset < 0 OrElse length < 0 OrElse offset + length > input2.Length Then
Throw New ArgumentOutOfRangeException("Selected range is outside the bounds of the input array")
End If
Return AppendInternal(initial, input2, offset, length)
End Function
''' <summary>
''' Computes CRC-3C from multiple buffers.
''' Call this method multiple times to chain multiple buffers.
''' </summary>
''' <param name="initial">
''' Initial CRC value for the algorithm. It is zero for the first buffer.
''' Subsequent buffers should have their initial value set to CRC value returned by previous call to this method.
''' </param>
''' <param name="input">Input buffer containing data to be checksummed.</param>
''' <returns>Accumulated CRC-32 of all buffers processed so far.</returns>
Public Shared Function Append(ByVal initial As UInteger, ByVal input As Byte()) As UInteger
If input Is Nothing Then
Throw New ArgumentNullException()
End If
Return AppendInternal(initial, input, 0, input.Length)
End Function
''' <summary>
''' Computes CRC-32 from input buffer.
''' </summary>
''' <param name="input">Input buffer with data to be checksummed.</param>
''' <param name="offset">Offset of the input data within the buffer.</param>
''' <param name="length">Length of the input data in the buffer.</param>
''' <returns>CRC-32 of the data in the buffer.</returns>
Public Shared Function Compute(ByVal input As Byte(), ByVal offset As Integer, ByVal length As Integer) As UInteger
Return Append(0, input, offset, length)
End Function
''' <summary>
''' Computes CRC-32 from input buffer.
''' </summary>
''' <param name="input">Input buffer containing data to be checksummed.</param>
''' <returns>CRC-32 of the buffer.</returns>
Public Shared Function Compute(ByVal input As Byte()) As UInteger
Return Append(0, input)
End Function
''' <summary>
''' Resets internal state of the algorithm. Used internally.
''' </summary>
Public Overrides Sub Initialize()
_currentCrc = 0
End Sub
''' <summary>
''' Appends CRC-32 from given buffer
''' </summary>
Protected Overrides Sub HashCore(ByVal input As Byte(), ByVal offset As Integer, ByVal length As Integer)
_currentCrc = AppendInternal(_currentCrc, input, offset, length)
End Sub
''' <summary>
''' Computes CRC-32 from <see cref="HashCore"/>
''' </summary>
Protected Overrides Function HashFinal() As Byte()
' Crc32 by dariogriffo uses big endian, so, we need to be compatible and return big endian too
Return New Byte() {CByte(_currentCrc >> 24 And &HFF), CByte(_currentCrc >> 16 And &HFF), CByte(_currentCrc >> 8 And &HFF), CByte(_currentCrc And &HFF)}
End Function
Private Shared ReadOnly _proxy As New SafeProxy()
Private Shared Function AppendInternal(ByVal initial As UInteger, ByVal input As Byte(), ByVal offset As Integer, ByVal length As Integer) As UInteger
If length > 0 Then
Return _proxy.Append(initial, input, offset, length)
Else
Return initial
End If
End Function
End Class
End Namespace
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