_crc32.cpp

几个封装完好的常用算法,md5,des,base64,crc32

//---------------------------------------------------------------------------


#pragma hdrstop

#include "_CRC32.h"

//---------------------------------------------------------------------------

#pragma package(smart_init)


void TCRC32::Init_CRC32_Table(void)
{
        //TODO: Add your source code here
        // This is the official polynomial used by CRC-32 in PKZip, WinZip and Ethernet.
        unsigned long 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);
	}
}

__fastcall TCRC32::TCRC32()
{
        //TODO: Add your source code here
        Init_CRC32_Table();
}

__fastcall TCRC32::~TCRC32()
{
        //TODO: Add your source code here
}
// This function uses the crc32_table lookup table to generate a CRC for csData
int TCRC32::Get_CRC(unsigned char * buffer, int dwSize)
{
        //TODO: Add your source code here
	// Be sure to use unsigned variables,
	// because negative values introduce high bits
	// where zero bits are required.
	unsigned long  crc(0xffffffff);
	int len;

	len = dwSize;
	// Perform the algorithm on each character
	// in the string, using the lookup table values.
	while(len--)
		crc = (crc >> 8) ^ crc32_table[(crc & 0xFF) ^ *buffer++];
	// Exclusive OR the result with the beginning value.
	return crc^0xffffffff;
}
// Reflection is a requirement for the official CRC-32 standard.
// You can create CRCs without it, but they won't conform to the standard.
unsigned long TCRC32::Reflect(unsigned long ref, unsigned char ch)
{
        //TODO: Add your source code here
        // Used only by Init_CRC32_Table()

	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;
}