/****************************************/
/* Copyright (c) 2004, 通信工程學(xué)院戴佳 */
/* All rights reserved.                 */
/* 作    者：戴佳                       */
/****************************************/

#include "CRC.h"

/* 按位求CRC */
uint bit_crc(uchar *ptr, uchar len)
{
	uchar i;
	uint crc = 0;
	while (len--!=0) 
	{
		for (i=0x80; i!=0; i/=2) 
		{
			if ((crc&0x8000)!=0) 
			{
				crc*=2; 			// 余式CRC乘以2 
				crc^=0x11021; 		// 再求CRC 
			}
			else
	 			crc*=2;
			if ((*ptr&i)!=0)  
				crc^=0x11021;		// 再加上本位的CRC 
		}
		ptr++;
	}
	return(crc);
}

/* 按字節(jié)查表求CRC */
uint byte_crc(uchar *ptr, uchar len) 
{
	uint crc;
	uchar da;

	/* CRC 余式表 */ 
	uint xdata crc_ta[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
	};
	crc = 0;
	while(len--!=0) 
	{
		da=(uchar) (crc/256); 	// 以8位二進(jìn)制數(shù)的形式暫存CRC的高8位 
		crc<<=8; 				// 左移8位，相當(dāng)于CRC的低8位乘以2的8次方 
		crc^=crc_ta[da^*ptr]; 	// 高8位和當(dāng)前字節(jié)相加后再查表求CRC，再加上以前的CRC   
		ptr++;
	}
	return(crc);
}


/* 按半字節(jié)查表求CRC */
uint halfbyte_crc(uchar *ptr, uchar len) 
{
	uint crc;
	uchar da;

	/* CRC余式表 */
	uint xdata crc_ta[16]=
	{ 			
		0x0000,0x1021,0x2042,0x3063,0x4084,0x50a5,0x60c6,0x70e7,
		0x8108,0x9129,0xa14a,0xb16b,0xc18c,0xd1ad,0xe1ce,0xf1ef
	};
	crc = 0;
	while(len--!=0) 
	{
		da=((uchar)(crc/256))/16; 	  // 暫存CRC的高四位 
		crc<<=4; 					  // CRC右移4位，相當(dāng)于取CRC的低12位
		crc^=crc_ta[da^(*ptr/16)]; 	  // CRC的高4位和本字節(jié)的前半字節(jié)相加后查表									計(jì)算CRC，然后加上上一次CRC的余數(shù) */
		da=((uchar)(crc/256))/16; 	  // 暫存CRC的高4位 
		crc<<=4; 					  // CRC右移4位，相當(dāng)于CRC的低12位
		crc^=crc_ta[da^(*ptr&0x0f)];  /* CRC的高4位和本字節(jié)的后半字節(jié)相加后查表
										 計(jì)算CRC，然后再加上上一次CRC的余數(shù) */
		ptr++;
	}
	return(crc);
}

/* 主程序 */
void main()
{
	uchar len;
	uint crc_bit;
	uint crc_byte;
	uint crc_halfbyte;

	len = 8;
	crc_bit = bit_crc(testdata,len);			// 調(diào)用按位求CRC子函數(shù)
	crc_byte = byte_crc(testdata,len);			// 調(diào)用按字節(jié)查表求CRC子函數(shù)
	crc_halfbyte = halfbyte_crc(testdata,len);	// 調(diào)用按半字節(jié)查表求CRC子函數(shù)
	
	while(1);	
}