因工作原因，前一阵子接触了CRC32校验问题，当时从网上找了一些实现校验的函数，但是不是缺胳膊就是少腿，要不就是程序错误，现提供一个正确的实现CRC32校验的函数和生成码表的函数。
校验函数：
unsigned long CRC32(char * DataBuf,unsigned long len)
{
unsigned int i;
unsigned long m_CRC = 0xFFFFFFFF;
char *pD;
pD = DataBuf;
for(i=0;i<len;i++)
{
m_CRC=crc32_table[(m_CRC^(*(pD+i)))&0xff] ^ (m_CRC>>8);
}
return ~m_CRC;
}
码表生成函数：
unsigned long int Reflect(unsigned long int ref, char ch)
{
unsigned long int value = 0;
int i;
// 交换bit0和bit7，bit1和bit6，类推
for(i = 1; i < (ch + 1); i++)
{
if(ref & 1)
value |= 1 << (ch - i);
ref >>= 1;
}
return value;
}
init_crc32_table()
{
unsigned long int crc,temp;
int i,j;
// 256个值
for(i = 0; i <= 0xFF; i++)
{
temp=Reflect(i, 8);
crc32_table[i]= temp<< 24;
for (j = 0; j < 8; j++)
{
unsigned long int t1,t2;
unsigned long int flag=crc32_table[i]&0x80000000;
t1=(crc32_table[i] << 1);
if(flag==0)
t2=0;
else
t2=ulPolynomial;
crc32_table[i] =t1^t2 ;
}
crc=crc32_table[i];
crc32_table[i] = Reflect(crc32_table[i], 32);
}
}
生成的码表如下：
0x0,0x77073096,0xee0e612c,0x990951ba,0x76dc419,0x706af48f,0xe963a535,0x9e6495a3,
0xedb8832,0x79dcb8a4,0xe0d5e91e,0x97d2d988,0x9b64c2b,0x7eb17cbd,0xe7b82d07,0x90bf1d91,
0x1db71064,0x6ab020f2,0xf3b97148,0x84be41de,0x1adad47d,0x6ddde4eb,0xf4d4b551,0x83d385c7,
0x136c9856,0x646ba8c0,0xfd62f97a,0x8a65c9ec,0x14015c4f,0x63066cd9,0xfa0f3d63,0x8d080df5,
0x3b6e20c8,0x4c69105e,0xd56041e4,0xa2677172,0x3c03e4d1,0x4b04d447,0xd20d85fd,0xa50ab56b,
0x35b5a8fa,0x42b2986c,0xdbbbc9d6,0xacbcf940,0x32d86ce3,0x45df5c75,0xdcd60dcf,0xabd13d59,
0x26d930ac,0x51de003a,0xc8d75180,0xbfd06116,0x21b4f4b5,0x56b3c423,0xcfba9599,0xb8bda50f,
0x2802b89e,0x5f058808,0xc60cd9b2,0xb10be924,0x2f6f7c87,0x58684c11,0xc1611dab,0xb6662d3d,
0x76dc4190,0x1db7106,0x98d220bc,0xefd5102a,0x71b18589,0x6b6b51f,0x9fbfe4a5,0xe8b8d433,
0x7807c9a2,0xf00f934,0x9609a88e,0xe10e9818,0x7f6a0dbb,0x86d3d2d,0x91646c97,0xe6635c01,
0x6b6b51f4,0x1c6c6162,0x856530d8,0xf262004e,0x6c0695ed,0x1b01a57b,0x8208f4c1,0xf50fc457,
0x65b0d9c6,0x12b7e950,0x8bbeb8ea,0xfcb9887c,0x62dd1ddf,0x15da2d49,0x8cd37cf3,0xfbd44c65,
0x4db26158,0x3ab551ce,0xa3bc0074,0xd4bb30e2,0x4adfa541,0x3dd895d7,0xa4d1c46d,0xd3d6f4fb,
0x4369e96a,0x346ed9fc,0xad678846,0xda60b8d0,0x44042d73,0x33031de5,0xaa0a4c5f,0xdd0d7cc9,
0x5005713c,0x270241aa,0xbe0b1010,0xc90c2086,0x5768b525,0x206f85b3,0xb966d409,0xce61e49f,
0x5edef90e,0x29d9c998,0xb0d09822,0xc7d7a8b4,0x59b33d17,0x2eb40d81,0xb7bd5c3b,0xc0ba6cad,
0xedb88320,0x9abfb3b6,0x3b6e20c,0x74b1d29a,0xead54739,0x9dd277af,0x4db2615,0x73dc1683,
0xe3630b12,0x94643b84,0xd6d6a3e,0x7a6a5aa8,0xe40ecf0b,0x9309ff9d,0xa00ae27,0x7d079eb1,
0xf00f9344,0x8708a3d2,0x1e01f268,0x6906c2fe,0xf762575d,0x806567cb,0x196c3671,0x6e6b06e7,
0xfed41b76,0x89d32be0,0x10da7a5a,0x67dd4acc,0xf9b9df6f,0x8ebeeff9,0x17b7be43,0x60b08ed5,
0xd6d6a3e8,0xa1d1937e,0x38d8c2c4,0x4fdff252,0xd1bb67f1,0xa6bc5767,0x3fb506dd,0x48b2364b,
0xd80d2bda,0xaf0a1b4c,0x36034af6,0x41047a60,0xdf60efc3,0xa867df55,0x316e8eef,0x4669be79,
0xcb61b38c,0xbc66831a,0x256fd2a0,0x5268e236,0xcc0c7795,0xbb0b4703,0x220216b9,0x5505262f,
0xc5ba3bbe,0xb2bd0b28,0x2bb45a92,0x5cb36a04,0xc2d7ffa7,0xb5d0cf31,0x2cd99e8b,0x5bdeae1d,
0x9b64c2b0,0xec63f226,0x756aa39c,0x26d930a,0x9c0906a9,0xeb0e363f,0x72076785,0x5005713,
0x95bf4a82,0xe2b87a14,0x7bb12bae,0xcb61b38,0x92d28e9b,0xe5d5be0d,0x7cdcefb7,0xbdbdf21,
0x86d3d2d4,0xf1d4e242,0x68ddb3f8,0x1fda836e,0x81be16cd,0xf6b9265b,0x6fb077e1,0x18b74777,
0x88085ae6,0xff0f6a70,0x66063bca,0x11010b5c,0x8f659eff,0xf862ae69,0x616bffd3,0x166ccf45,
0xa00ae278,0xd70dd2ee,0x4e048354,0x3903b3c2,0xa7672661,0xd06016f7,0x4969474d,0x3e6e77db,
0xaed16a4a,0xd9d65adc,0x40df0b66,0x37d83bf0,0xa9bcae53,0xdebb9ec5,0x47b2cf7f,0x30b5ffe9,
0xbdbdf21c,0xcabac28a,0x53b39330,0x24b4a3a6,0xbad03605,0xcdd70693,0x54de5729,0x23d967bf,
0xb3667a2e,0xc4614ab8,0x5d681b02,0x2a6f2b94,0xb40bbe37,0xc30c8ea1,0x5a05df1b,0x2d02ef8d
The End.
