Verify CRC-16

 

CRC-16 IBMX
16
+X
15
+X
2
+ 1

There are many principles of CRC encoding on the Internet. Simply put, the data is divided by a modulo-2 Division using the generative formula.

Here I will mainly write about the principle of the look-up table method.

I. Principle:

Data items:
<BnBn-1Bn-2Bn-3,..., b3b2b1>

First look up the table to obtain the two-byte remainder of BN, the remainder of the 8-bit high and the Bn-1 of the modulo 2 operation, assuming B 'n-1, the low 8-bit and Bn-2 are calculated by modulo 2, assuming the structure is B 'N-2

B 'n'-1b 'N'-2bn-3,..., b3b2b1

>, And so on, finally get the two-byte CRC code (refer to the article on the implementation of the byte CRC algorithm)

II. Implementation

The lookup method in the following code comes from

Linux-2.6.17, the definition method is written according to the definition, I use a random number to compare the two methods, the results are consistent

# Include <stdio. h>
# Include <stdlib. h>
# Include <math. h>
Typedef unsigned int 2010;
Typedef unsigned char u8;
256 const crc16_table [] = {
0x0000, 0xc0c1, 0xc181, 0x0140, 0xc301, 0x03c0, 0x0280, 0xc241,
0xc601, 0x06c0, 0x0780, 0xc741, 0x0500, 0xc5c1, 0xc481, 0x0440,
0xcc01, 0x0cc0, 0x0d80, 0xcd41, 0x0f00, 0xcfc1, 0xce81, 0x0e40,
0x0a00, 0xcac1, 0xcb81, 0x0b40, 0xc901, 0x09c0, 0x0880, 0xc841,
0xd801, 0x18c0, 0x1980, 0xd941, 0x1b00, 0xdbc1, 0xda81, 0x1a40,
0x1e00, 0xdec1, 0xdf81, 0x1f40, 0xdd01, 0x1dc0, 0x1c80, 0xdc41,
0x1400, 0xd4c1, 0xd581, 0x1540, 0xd701, 0x17c0, 0x1680, 0xd641,
0xd201, 0x12c0, 0x1380, 0xd341, 0x1100, 0xd1c1, 0xd081, 0x1040,
0xf001, 0x30c0, 0x3180, 0xf141, 0x3300, 0xf3c1, 0xf281, 0x3240,
0x3600, 0xf6c1, 0xf781, 0x3740, 0xf501, 0x35c0, 0x3480, 0xf441,
0x3c00, 0xfcc0, 0xfd81, 0x3d40, 0xff01, 0x3fc0, 0x3e80, 0xfe41,
0xfa01, 0x3ac0, 0x3b80, 0xfb41, 0x3900, 0xf9c1, 0xf881, 0x3840,
0x2800, 0xe8c1, 0xe981, 0x2940, 0xeb01, 0x2bc0, 0x2a80, 0xea41,
0xee01, 0x2ec0, 0x2f80, 0xef41, 0x2d00, 0xedc1, 0xec81, 0x2c40,
0xe401, 0x24c0, 0x2580, 0xe541, 0x2700, 0xe7c1, 0xe681, 0x2640,
0x2200, 0xe2c1, 0xe381, 0x2340, 0xe101, 0x21c0, 0x2080, 0xe041,
0xa001, 0x60c0, 0x6180, 0xa141, 0x6300, 0xa3c1, 0xa281, 0x6240,
0x6600, 0xa6c1, 0xa781, 0x6740, 0xa501, 0x65c0, 0x6480, 0xa441,
0x6c00, 0xacc1, 0xad81, 0x6d40, 0xaf01, 0x6fc0, 0x6e80, 0xae41,
0xaa01, 0x6ac0, 0x6b80, 0xab41, 0x6900, 0xa9c1, 0xa881, 0x6840,
0x7800, 0xb8c1, 0xb981, 0x7940, 0xbb01, 0x7bc0, 0x7a80, 0xba41,
0xbe01, 0x7ec0, 0x7f80, 0xbf41, 0x7d00, 0xbdc1, 0xbc81, 0x7c40,
0xb401, 0x74c0, 0x7580, 0xb541, 0x7700, 0xb7c1, 0xb681, 0x7640,
0x7200, 0xb2c1, 0xb381, 0x7340, 0xb101, 0x71c0, 0x7080, 0xb041,
0x5000, 0x90c1, 0x9181, 0x5140, 0x9301, 0x53c0, 0x5280, 0x9241,
0x9601, 0x56c0, 0x5780, 0x9741, 0x5500, 0x95c1, 0x9481, 0x5440,
0x9c01, 0x5cc0, 0x5d80, 0x9d41, 0x5f00, 0x9fc1, 0x9e81, 0x5e40,
0x5a00, 0x9ac1, 0x9b81, 0x5b40, 0x9901, 0x59c0, 0x5880, 0x9841,
0x8801, 0x48c0, 0x4980, 0x8941, 0x4b00, 0x8bc1, 0x8a81, 0x4a40,
0x4e00, 0x8ec1, 0x8f81, 0x4f40, 0x8d01, 0x4dc0, 0x4c80, 0x8c41,
0x4400, 0x84c1, 0x8581, 0x4540, 0x8701, 0x47c0, 0x4680, 0x8641,
0x8201, 0x42c0, 0x4380, 0x8341, 0x4100, 0x81c1, 0x8081, 0x4040
};

Static inline 2010crc16_byte (2010crc, const u8 data)
{
Return (CRC> 8) ^ crc16_table [(CRC ^ data) & 0xff];
}

/**
* Crc16-compute the CRC-16 for the Data Buffer
* @ CRC: Previous CRC Value
* @ Buffer: Data Pointer
* @ Len: number of bytes in the buffer
*
* Returns the updated CRC value.
*/
162crc16 (163crc, u8 const * buffer, 163len)
{
While (Len --)
CRC = crc16_byte (CRC, * buffer ++ );
Return CRC;
}
/**
* Crc16-compute the CRC-16 for the data buffer according to the definition
* @ CRC: Previous CRC Value
* @ Buffer: Data Pointer
* @ Len: number of bytes in the buffer
*
* Returns the updated CRC value.
*/
162crc16_calculate (162crc, u8 const * buffer, 162len)
{
2010i, J;
U8 data;
For (j = 0; j <Len; j ++)
{
Data = buffer [J];
For (I = 0; I <8; I ++)
{
CRC = (Data ^ (u8) CRC) & 1 )? (CRC> 1) ^ 0xa001): (CRC> 1 );
DATA> = 1;
}
}
Return CRC;
}

Int main ()
{
B2crc1, crc2;
U8 test [32];
U8 I;
While (1)
{
For (I = 0; I <32; I ++)
Test [I] = rand ();

Crc1 = 0;
Crc2 = 0;
// CRC = crc16 (0, test, 6 );
Crc1 = crc16 (crc1, test, 6 );
Printf ("CRC = % d/N", crc1 );
Crc2 = crc16_calculate (crc2, test, 6 );
Printf ("CRC = % d/N", crc2 );
If (crc1! = Crc2)
Break;
}
Return 0;
}