#include "crc8.h"
/*
The 256-byte table is as follows:
table $00 ;entry 0
*/
#if 1
code const unsigned char crc8_table[] = 
{
	0x00,0x07,0x0E,0x09,0x1C,0x1B,0x12,0x15,0x38,0x3F,0x36,0x31,0x24,0x23,0x2A,0x2D,	//0x00~0x0f
	0x70,0x77,0x7E,0x79,0x6C,0x6B,0x62,0x65,0x48,0x4F,0x46,0x41,0x54,0x53,0x5A,0x5D,	//0x10~0x1f
	0xE0,0xE7,0xEE,0xE9,0xFC,0xFB,0xF2,0xF5,0xD8,0xDF,0xD6,0xD1,0xC4,0xC3,0xCA,0xCD,	//0x20~0x2f
	0x90,0x97,0x9E,0x99,0x8C,0x8B,0x82,0x85,0xA8,0xAF,0xA6,0xA1,0xB4,0xB3,0xBA,0xBD,	//0x30~0x3f
	0xC7,0xC0,0xC9,0xCE,0xDB,0xDC,0xD5,0xD2,0xFF,0xF8,0xF1,0xF6,0xE3,0xE4,0xED,0xEA,
	0xB7,0xB0,0xB9,0xBE,0xAB,0xAC,0xA5,0xA2,0x8F,0x88,0x81,0x86,0x93,0x94,0x9D,0x9A,
	0x27,0x20,0x29,0x2E,0x3B,0x3C,0x35,0x32,0x1F,0x18,0x11,0x16,0x03,0x04,0x0D,0x0A,
	0x57,0x50,0x59,0x5E,0x4B,0x4C,0x45,0x42,0x6F,0x68,0x61,0x66,0x73,0x74,0x7D,0x7A,
	0x89,0x8E,0x87,0x80,0x95,0x92,0x9B,0x9C,0xB1,0xB6,0xBF,0xB8,0xAD,0xAA,0xA3,0xA4,
	0xF9,0xFE,0xF7,0xF0,0xE5,0xE2,0xEB,0xEC,0xC1,0xC6,0xCF,0xC8,0xDD,0xDA,0xD3,0xD4,
	0x69,0x6E,0x67,0x60,0x75,0x72,0x7B,0x7C,0x51,0x56,0x5F,0x58,0x4D,0x4A,0x43,0x44,
	0x19,0x1E,0x17,0x10,0x05,0x02,0x0B,0x0C,0x21,0x26,0x2F,0x28,0x3D,0x3A,0x33,0x34,
	0x4E,0x49,0x40,0x47,0x52,0x55,0x5C,0x5B,0x76,0x71,0x78,0x7F,0x6A,0x6D,0x64,0x63,
	0x3E,0x39,0x30,0x37,0x22,0x25,0x2C,0x2B,0x06,0x01,0x08,0x0F,0x1A,0x1D,0x14,0x13,
	0xAE,0xA9,0xA0,0xA7,0xB2,0xB5,0xBC,0xBB,0x96,0x91,0x98,0x9F,0x8A,0x8D,0x84,0x83,
	0xDE,0xD9,0xD0,0xD7,0xC2,0xC5,0xCC,0xCB,0xE6,0xE1,0xE8,0xEF,0xFA,0xFD,0xF4,0xF3
};

unsigned char crc8_fast_compute(unsigned char xdata *p,unsigned char length)
{
	unsigned char crc8;
	unsigned char i;
	unsigned char offset;

	crc8 = 0;
	for(i = 0; i < length; i++)
	{
		offset = crc8 ^ *(p + i);
		crc8 = crc8_table[offset];
	}
	return crc8 ^ 0x55;
}

#endif

/*
* This code performs a table lookup to determine the new CRC value 
* for each byte received
* Registers used:
* 		Accumulator A
* 		Memory register CRC
* 		Temporary storage in_temp
*
* Input: Memory register CRC contains the previously calculated CRC value
* Accumulator A contains the input data byte
* Output: Memory register CRC contains the current CRC value
*/

/*
init_byte:
sta in_temp ; //store the two nibbles in a temporary storage high_nibble:

// create the table index for the most significant nibble
// A <- (MS nibble of input byte ^ MS nibble of CRC)
eor CRC ; 	//get the XOR of the most significant nibble with CRC into ACC
tax  ; 		//prepare index register to point to the right table entry
lsrx ; 		//shift contents of ACC 4 times to the right to obtain high nibble
lsrx ; 		//table index. Fill the vacant bits with zeros
lsrx ; 		//some MCUs have more efficient instructions to perform this
lsrx ; 		//table index is now into ACC

// calculate the new CRC value: A <- (previous CRC) ^ table(index)
lda CRC ; 	//retrieve the previous CRC value
and #$0F
eor table_rev,x ; //get the new CRC value. ACC contains now the new CRC

sta CRC ; //save the new CRC value low_nibble:

// create the table index for the least significant nibble
// A <- ( LS nibble of input byte ^ MS nibble of CRC)
eor in_temp ; 	//get the XOR of the high CRC nibble with the low nibble of input
and #$0F  ; 		//mask high bits (next nibble in the message)
tax ; 			//prepare index register

// calculate the new CRC value: A <- (previous CRC) ^ table(index)
lda CRC ; 		//get previous CRC value
and #$F0;
eor table,x; 	//get new CRC value
sta CRC; 		//save it into the CRC register
*/
unsigned char crc8_compute(unsigned char xdata *p,unsigned char length)
{
	//The tables used are the following:
	code const unsigned char table[] = {
		0x00,0x07,0x0E,0x09,0x1C,0x1B,0x12,0x15,
		0x38,0x3F,0x36,0x31,0x24,0x23,0x2A,0x2D};

	code const unsigned char table_rev[] = {
		0x00,0x70,0xE0,0x90,0xC1,0xB1,0x21,0x51,
		0x83,0xF3,0x63,0x13,0x42,0x32,0xA2,0xD2};

	unsigned char crc8;	unsigned char i;unsigned char offset;unsigned char temp,crc8_temp;
	crc8 = 0x00;

	for(i = 0; i < length; i++)
	{
		temp = *(p + i);//store the two nibbles in a temporary storage

		offset = temp ^ crc8;
		offset >>= 4;

		crc8_temp = crc8 & 0x0f;
		crc8 = crc8_temp ^ table_rev[offset];//get the new CRC value.

		offset = crc8 ^ temp;
		offset &= 0x0f;
		crc8_temp = crc8 & 0xf0;
		crc8 = crc8_temp ^ table[offset];
	}
	return crc8 ^ 0x55;
}

/*
* Function name		: append_crc8_result
* Function describe	: compute the data crc8 result and append the result byte
*					  into the address following the data.	 
*					  crc stand: CRC8 (0x107)
*					  crc  polynomial: G(x)= (x^8+x^2+x^1+1)
* Input				: p:the datas point 
*					: length:the data length,length < 0xff
* Output 			: none
* Ram be effected	: following the data addtess is stored by crc8 result.
* global variable	: none
* Called module		: crc8_compute
*
* Data				: 2003.12.16
*/
void append_crc8_result(unsigned char *p,unsigned char length)
{
	*(p + length) = crc8_compute(p,length);
}

/*
* Function name		: verfify_crc8_ok
* Function describe	: verify the datas's crc8 check are correct
*					  crc stand: CRC8 (0x107)
*					  crc  polynomial: G(x)= (x^8+x^2+x^1+1)
*
* Input			: p:the datas point 
*					: length:the data length,length <= 0xff
* Output 			: CRC_CORRECT:	the datas sum check result are correct.
* 					  CRC_INCORRECT:the datas sum check result are false.
* global variable	: none
* Called module	: crc8_compute
*
* Data				: 2003.12.16
*/
#define CRC_CORRECT			1
#define CRC_INCORRECT		0
#define CHECK_CRC_RESET	0xf9
bit verfify_crc8_ok(unsigned char xdata *p,unsigned char length)
{
	if(crc8_fast_compute(p,length) == CHECK_CRC_RESET)
	{
		return CRC_CORRECT;
	}
	else
	{
		return CRC_INCORRECT;
	}
}