crc check sum test in c language

#include<stdio.h>

static const unsigned int crctab16[] =
{
 0X0000, 0X1189, 0X2312, 0X329B, 0X4624, 0X57AD, 0X6536, 0X74BF,
 0X8C48, 0X9DC1, 0XAF5A, 0XBED3, 0XCA6C, 0XDBE5, 0XE97E, 0XF8F7,
 0X1081, 0X0108, 0X3393, 0X221A, 0X56A5, 0X472C, 0X75B7, 0X643E,
 0X9CC9, 0X8D40, 0XBFDB, 0XAE52, 0XDAED, 0XCB64, 0XF9FF, 0XE876,
 0X2102, 0X308B, 0X0210, 0X1399, 0X6726, 0X76AF, 0X4434, 0X55BD,
 0XAD4A, 0XBCC3, 0X8E58, 0X9FD1, 0XEB6E, 0XFAE7, 0XC87C, 0XD9F5,
 0X3183, 0X200A, 0X1291, 0X0318, 0X77A7, 0X662E, 0X54B5, 0X453C,
 0XBDCB, 0XAC42, 0X9ED9, 0X8F50, 0XFBEF, 0XEA66, 0XD8FD, 0XC974,
 0X4204, 0X538D, 0X6116, 0X709F, 0X0420, 0X15A9, 0X2732, 0X36BB,
 0XCE4C, 0XDFC5, 0XED5E, 0XFCD7, 0X8868, 0X99E1, 0XAB7A, 0XBAF3,
 0X5285, 0X430C, 0X7197, 0X601E, 0X14A1, 0X0528, 0X37B3, 0X263A,
 0XDECD, 0XCF44, 0XFDDF, 0XEC56, 0X98E9, 0X8960, 0XBBFB, 0XAA72,
 0X6306, 0X728F, 0X4014, 0X519D, 0X2522, 0X34AB, 0X0630, 0X17B9,
 0XEF4E, 0XFEC7, 0XCC5C, 0XDDD5, 0XA96A, 0XB8E3, 0X8A78, 0X9BF1,
 0X7387, 0X620E, 0X5095, 0X411C, 0X35A3, 0X242A, 0X16B1, 0X0738,
 0XFFCF, 0XEE46, 0XDCDD, 0XCD54, 0XB9EB, 0XA862, 0X9AF9, 0X8B70,
 0X8408, 0X9581, 0XA71A, 0XB693, 0XC22C, 0XD3A5, 0XE13E, 0XF0B7,
 0X0840, 0X19C9, 0X2B52, 0X3ADB, 0X4E64, 0X5FED, 0X6D76, 0X7CFF,
 0X9489, 0X8500, 0XB79B, 0XA612, 0XD2AD, 0XC324, 0XF1BF, 0XE036,
 0X18C1, 0X0948, 0X3BD3, 0X2A5A, 0X5EE5, 0X4F6C, 0X7DF7, 0X6C7E,
 0XA50A, 0XB483, 0X8618, 0X9791, 0XE32E, 0XF2A7, 0XC03C, 0XD1B5,
 0X2942, 0X38CB, 0X0A50, 0X1BD9, 0X6F66, 0X7EEF, 0X4C74, 0X5DFD,
 0XB58B, 0XA402, 0X9699, 0X8710, 0XF3AF, 0XE226, 0XD0BD, 0XC134,
 0X39C3, 0X284A, 0X1AD1, 0X0B58, 0X7FE7, 0X6E6E, 0X5CF5, 0X4D7C,
 0XC60C, 0XD785, 0XE51E, 0XF497, 0X8028, 0X91A1, 0XA33A, 0XB2B3,
 0X4A44, 0X5BCD, 0X6956, 0X78DF, 0X0C60, 0X1DE9, 0X2F72, 0X3EFB,
 0XD68D, 0XC704, 0XF59F, 0XE416, 0X90A9, 0X8120, 0XB3BB, 0XA232,
 0X5AC5, 0X4B4C, 0X79D7, 0X685E, 0X1CE1, 0X0D68, 0X3FF3, 0X2E7A,
 0XE70E, 0XF687, 0XC41C, 0XD595, 0XA12A, 0XB0A3, 0X8238, 0X93B1,
 0X6B46, 0X7ACF, 0X4854, 0X59DD, 0X2D62, 0X3CEB, 0X0E70, 0X1FF9,
 0XF78F, 0XE606, 0XD49D, 0XC514, 0XB1AB, 0XA022, 0X92B9, 0X8330,
 0X7BC7, 0X6A4E, 0X58D5, 0X495C, 0X3DE3, 0X2C6A, 0X1EF1, 0X0F78,
};
// calculate the 16-bit CRC of data with predetermined length.
unsigned int GetCrc16(const unsigned char* pData, int nLength)
{
    unsigned int fcs = 0xffff; // initialization
    while(nLength>0)
    {
        fcs = (fcs >> 8) ^ crctab16[(fcs ^ *pData) & 0xff];
        nLength--;
        pData++;
    }
 return ~fcs; // negated
 }

 //78 78 0D 01 01 23 45 67 89 01 23 45 00 01 8C DD 0D 0A
char* packet_framing(unsigned char protocol_num,unsigned char *infomation_content,unsigned short int counter)
{
    unsigned char start_bytes[2]={0x78,0x78,0x00};
    unsigned char stop_bytes[2]={0x0d,0x0a,0x00};
    unsigned char u8_protocol_len = 0;
    unsigned char gt06_protocol[100]={0};
    unsigned char gt06_protocol2[18];
    unsigned char gt06_protocol3[18];
    unsigned char *gt06_protocol4;
    unsigned short int u8_len = 0;
    unsigned short int u8_check_cum = 0;

    gt06_protocol4 = malloc(sizeof (char) * 30);

    memset(gt06_protocol,0x00,sizeof(gt06_protocol));
    strcpy(gt06_protocol,start_bytes);
    gt06_protocol[2] = 5 + strlen((char *)infomation_content);// packect length
    gt06_protocol[3] = protocol_num;// protocol number

    strncat(gt06_protocol,infomation_content,strlen((char *)infomation_content));// information content ex : imei

     u8_len = strlen((char *)gt06_protocol);

    gt06_protocol[u8_len++] = counter>>8;
    gt06_protocol[u8_len++] = counter;

    u8_check_cum = GetCrc16(gt06_protocol+2,u8_len-2);
   // printf("cnt = %x ",u8_check_cum);

    gt06_protocol[u8_len++] = u8_check_cum>>8;
    // printf("cnt = %x ",u8_check_cum);
    gt06_protocol[u8_len++] = u8_check_cum;
    //printf("cnt = %x ",u8_check_cum);
    gt06_protocol[u8_len++] = stop_bytes[0];
    //printf("stop byte = %x ",gt06_protocol);
    gt06_protocol[u8_len++] = stop_bytes[1];
     //printf("stop byte = %x ",gt06_protocol);

    for(char i=0;i<u8_len;i++)
    {
        printf("%x ",gt06_protocol[i]);
        sprintf(gt06_protocol2,"%x ",gt06_protocol[i]);
        strcat(gt06_protocol3,gt06_protocol2);
    }
    gt06_protocol4 = gt06_protocol3;
   //printf("in fun=%x ",gt06_protocol4);
    return gt06_protocol4;
}

int main()
{
    unsigned short int check_sum = 0;
     char *packet_reply;

    unsigned short int serial_num = 0x01;
  //  78 78 1F 12 08 69 86 70 33 30 80 42 00 01 8C DD 0D 0A
    unsigned char imei_num[10]={0x08,0x69,0x86,0x70,0x33,0x30,0x80,0x42,0x00};
   // check_sum = GetCrc16(test,12);
    packet_reply = packet_framing(serial_num,imei_num,serial_num);

    printf("\n main=%s\n",packet_reply);

    return 0;
}