www.pudn.com > CRC32.rar > CRC32.cpp

 
/* 
	Copyright 2006 - 2008, All Rights Reserved. 
 
	CRC32算法实现 
 
	作者	- 张鲁夺(zhangluduo) 
	MSN		- zhangluduo@msn.com 
	QQ群	- 34064264 
 
	为所有爱我的人和我爱的人努力! 
*/ 
 
#include "stdafx.h" 
#include "CRC32.h" 
 
CRC32::CRC32() 
{ 
	// init CRC-32 table 
    // This is the official polynomial used by CRC-32 
    unsigned long ulPolynomial = 0x04C11DB7; 
 
    // 256 values representing ASCII character codes. 
    for (int i = 0; i <= 0xFF; i++) 
    { 
        m_Table[i] = Reflect(i, 8) << 24; 
        for (int j = 0; j < 8; j++) 
            m_Table[i] = (m_Table[i] << 1) ^ (m_Table[i] & (1 << 31) ? ulPolynomial : 0); 
        m_Table[i] = Reflect(m_Table[i], 32); 
    } 
} 
 
CRC32::~CRC32() 
{ 
 
} 
 
unsigned long CRC32::Reflect(unsigned long ref, char ch) 
{ 
    unsigned long 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; 
} 
 
void CRC32::CRCUpdate(unsigned char* buffer, unsigned long size, unsigned long &Result) 
{ 
    while (size--) 
        Result = (Result >> 8) ^ m_Table[(Result & 0xFF) ^ *buffer++]; 
} 
 
void CRC32::CRCInit(unsigned long &Result) 
{ 
	Result = 0xFFFFFFFF; 
} 
void CRC32::CRCFinal(unsigned long &Result) 
{ 
	Result ^= 0xFFFFFFFF; 
}