|
|
Source File
// CRCdemo.cpp
void CRCdemo::Init_CRC32_Table()
{// Call this function only once to initialize the CRC table.
// This is the official polynomial used by CRC-32
// in PKZip, WinZip and Ethernet.
ULONG ulPolynomial = 0x04c11db7;
// 256 values representing ASCII character codes.
for(int i = 0; i <= 0xFF; i++)
{
crc32_table[i]=Reflect(i, 8) << 24;
for (int j = 0; j < 8; j++)
crc32_table[i] = (crc32_table[i] << 1) ^ (crc32_table[i] & (1 << 31) ? ulPolynomial : 0);
crc32_table[i] = Reflect(crc32_table[i], 32);
}
}
ULONG CRCdemo::Reflect(ULONG ref, char ch)
{// Used only by Init_CRC32_Table().
ULONG value(0);
// Swap bit 0 for bit 7
// bit 1 for bit 6, etc.
for(int i = 1; i < (ch + 1); i++)
{
if(ref & 1)
value |= 1 << (ch - i);
ref >>= 1;
}
return value;
}
int CRCdemo::Get_CRC(CString& text)
{ // Pass a text string to this function and it will return the CRC.
// Once the lookup table has been filled in by the two functions above,
// this function creates all CRCs using only the lookup table.
// Note that CString is an MFC class.
// If you don't have MFC, use the function below instead.
// Be sure to use unsigned variables,
// because negative values introduce high bits
// where zero bits are required.
// Start out with all bits set high.
ULONG ulCRC(0xffffffff);
int len;
unsigned char* buffer;
// Get the length.
len = text.GetLength();
// Save the text in the buffer.
buffer = (unsigned char*)(LPCTSTR)text;
// Perform the algorithm on each character
// in the string, using the lookup table values.
while(len--)
ulCRC = (ulCRC >> 8) ^ crc32_table[(ulCRC & 0xFF) ^ *buffer++];
// Exclusive OR the result with the beginning value.
return ulCRC ^ 0xffffffff;
}
E-mail: 
info@telesys.ru
