建立 crc32.cpp
代码如下：
---------------------------------------------------------------------------------
//kwanhong Young 2004-9-1
unsigned long CRCTable[256];
/*
int main(int argc, char* argv[])
{
Init();
unsigned long r=Update((unsigned char *)("ABCDEFG"), 7,0xFFFFFFFF);
printf("result is:%d",r);
return 0;
}
*/
//void Init()
extern "C" void __stdcall Init()
{
unsigned long crc, i, j;
unsigned long poly = 0xEDB88320;
for(i=0; i<256; i++)
{
crc = i;
for(j=8; j>0; j--)
{
if(crc & 1)
crc = (crc >> 1) ^ poly;
else
crc >>= 1;
}
CRCTable[i] = crc;
}
}
extern "C" unsigned long __stdcall Update(unsigned char *buffer,long length, unsigned long crc)
{
//unsigned long crc = 0xFFFFFFFF;
unsigned char *ptr = buffer;
while(length > 0)
{
crc = ((crc >> 8) & 0x00FFFFFF) ^ CRCTable[(crc ^ *ptr) & 0xFF];
ptr++;
length--;
}
return crc;
}
创建 crc32.def
代码如下：
---------------------------------------------------------------------------
EXPORTS
Init
Update
然后就可以编译成 DLL 了。
现在用VB新建一个 Class。代码如下：
-------------------------------------------------------------------------
Private Declare Sub CRC32Init Lib "kw_crc32.dll" Alias "Init" ()
Private Declare Function CRC32Update Lib "kw_crc32.dll" Alias "Update" (db As Any, ByVal length As Long, ByVal crcvalue As Long) As Long
Private m_lValue As Long
Private Sub Class_Initialize()
'//make crc32 table
CRC32Init
m_lValue = &HFFFFFFFF
End Sub
Public Sub Reset()
m_lValue = &HFFFFFFFF
End Sub
Public Sub Encode(bytData() As Byte, ByVal iLen As Long)
m_lValue = CRC32Update(bytData(0), iLen, m_lValue)
End Sub
Public Sub EncodePtr(ByVal ptbytData As Long, ByVal iLen As Long)
'//use data pointer
m_lValue = CRC32Update(ByVal ptbytData, iLen, m_lValue)
End Sub
Public Function GetValue() As String
GetValue = Right("00000000" & Hex$(m_lValue Xor &HFFFFFFFF), 8)
End Function
Public Function EncodeString(SourceString As String) As String
'// Function to digest a text string and output the result as a string
'// of hexadecimal characters.
Dim bytData() As Byte
m_lValue = &HFFFFFFFF
If Len(SourceString) = 0 Then
ReDim bytData(0)
EncodeString = "00000000"
Else
bytData = StrConv(SourceString, vbFromUnicode)
m_lValue = CRC32Update(bytData(0), UBound(bytData) + 1, m_lValue)
End If
EncodeString = Right("00000000" & Hex$(m_lValue Xor &HFFFFFFFF), 8)
End Function
Public Function SaveState() As String
'//save the state
SaveState = m_lValue
End Function
Public Function LoadState(s As String) As Boolean
'//load the state
m_lValue = s
LoadState = True
End Function
现在就可以在VB里面实现高速的CRC32 运算。