차트법의 crc 검사 알고리즘

/*
* Copy right     : 

* File name      : CRC16.c
* Author         : Roger.luo
* version        : V1.0
* Modified date  : 2014/6/14
* Description    :  CRC16      CRC16-CCITT
*     x^16 + x^12 + x^5 + 1    
*/
//CRC16-CCITT   
const unsigned short crc16_table[256] =
{
     0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
     0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef,
     0x1231,0x0210,0x3273,0x2252,0x52b5,0x4294,0x72f7,0x62d6,
     0x9339,0x8318,0xb37b,0xa35a,0xd3bd,0xc39c,0xf3ff,0xe3de,
     0x2462,0x3443,0x0420,0x1401,0x64e6,0x74c7,0x44a4,0x5485,
     0xa56a,0xb54b,0x8528,0x9509,0xe5ee,0xf5cf,0xc5ac,0xd58d,
     0x3653,0x2672,0x1611,0x0630,0x76d7,0x66f6,0x5695,0x46b4,
     0xb75b,0xa77a,0x9719,0x8738,0xf7df,0xe7fe,0xd79d,0xc7bc,
     0x48c4,0x58e5,0x6886,0x78a7,0x0840,0x1861,0x2802,0x3823,
     0xc9cc,0xd9ed,0xe98e,0xf9af,0x8948,0x9969,0xa90a,0xb92b,
     0x5af5,0x4ad4,0x7ab7,0x6a96,0x1a71,0x0a50,0x3a33,0x2a12,
     0xdbfd,0xcbdc,0xfbbf,0xeb9e,0x9b79,0x8b58,0xbb3b,0xab1a,
     0x6ca6,0x7c87,0x4ce4,0x5cc5,0x2c22,0x3c03,0x0c60,0x1c41,
     0xedae,0xfd8f,0xcdec,0xddcd,0xad2a,0xbd0b,0x8d68,0x9d49,
     0x7e97,0x6eb6,0x5ed5,0x4ef4,0x3e13,0x2e32,0x1e51,0x0e70,
     0xff9f,0xefbe,0xdfdd,0xcffc,0xbf1b,0xaf3a,0x9f59,0x8f78,
     0x9188,0x81a9,0xb1ca,0xa1eb,0xd10c,0xc12d,0xf14e,0xe16f,
     0x1080,0x00a1,0x30c2,0x20e3,0x5004,0x4025,0x7046,0x6067,
     0x83b9,0x9398,0xa3fb,0xb3da,0xc33d,0xd31c,0xe37f,0xf35e,
     0x02b1,0x1290,0x22f3,0x32d2,0x4235,0x5214,0x6277,0x7256,
     0xb5ea,0xa5cb,0x95a8,0x8589,0xf56e,0xe54f,0xd52c,0xc50d,
     0x34e2,0x24c3,0x14a0,0x0481,0x7466,0x6447,0x5424,0x4405,
     0xa7db,0xb7fa,0x8799,0x97b8,0xe75f,0xf77e,0xc71d,0xd73c,
     0x26d3,0x36f2,0x0691,0x16b0,0x6657,0x7676,0x4615,0x5634,
     0xd94c,0xc96d,0xf90e,0xe92f,0x99c8,0x89e9,0xb98a,0xa9ab,
     0x5844,0x4865,0x7806,0x6827,0x18c0,0x08e1,0x3882,0x28a3,
     0xcb7d,0xdb5c,0xeb3f,0xfb1e,0x8bf9,0x9bd8,0xabbb,0xbb9a,
     0x4a75,0x5a54,0x6a37,0x7a16,0x0af1,0x1ad0,0x2ab3,0x3a92,
     0xfd2e,0xed0f,0xdd6c,0xcd4d,0xbdaa,0xad8b,0x9de8,0x8dc9,
     0x7c26,0x6c07,0x5c64,0x4c45,0x3ca2,0x2c83,0x1ce0,0x0cc1,
     0xef1f,0xff3e,0xcf5d,0xdf7c,0xaf9b,0xbfba,0x8fd9,0x9ff8,
     0x6e17,0x7e36,0x4e55,0x5e74,0x2e93,0x3eb2,0x0ed1,0x1ef0
};
/*-----------------------------------------------------------
    *Function name :CRC16
    *Description   :CRC  (   ->x^16 + x^12 + x^5 + 1 )
    *Input         :buf 
    *reval         :crc code
------------------------------------------------------------*/
unsigned short crc16(void *buf,int count)
{
    unsigned char *ptr = (unsigned char *)buf;
    unsigned short crc_reg = 0xffff;        /*   ---------*/
    while (count--) 
    {
        crc_reg = (crc_reg << 8) ^ crc16_table[( (crc_reg >> 8) ^ *ptr++ ) & 0xff];
    } 
    return ~crc_reg;                        
}