www.pudn.com > speakfs72.zip > CRC.C, change:2002-01-05,size:3407b


/* 
		Cyclic redundancy check calculation routines 
 
				John Walker  --  May 1973 
 
*/ 
 
/*	This is the precomputed remainder table for generating and 
	checking cyclic redundancy check characters.  */ 
 
#ifdef MODEM 
static unsigned char low8[] = { 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
	0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0, 
	0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1, 
	0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1, 
	0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
	0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1, 
	0x81,0x40,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
	0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0, 
	0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
	0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
	0x01,0xC0,0x80,0x41,0x00,0xC1,0x81,0x40,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40,0x00,0xC1,0x81,0x40, 
	0x01,0xC0,0x80,0x41,0x01,0xC0,0x80,0x41,0x00,0xC1, 
	0x81,0x40,0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41, 
	0x00,0xC1,0x81,0x40,0x01,0xC0,0x80,0x41,0x01,0xC0, 
	0x80,0x41,0x00,0xC1,0x81,0x40 
}; 
 
static unsigned char high8[] = { 
	0x00,0xC0,0xC1,0x01,0xC3,0x03,0x02,0xC2,0xC6,0x06, 
	0x07,0xC7,0x05,0xC5,0xC4,0x04,0xCC,0x0C,0x0D,0xCD, 
	0x0F,0xCF,0xCE,0x0E,0x0A,0xCA,0xCB,0x0B,0xC9,0x09, 
	0x08,0xC8,0xD8,0x18,0x19,0xD9,0x1B,0xDB,0xDA,0x1A, 
	0x1E,0xDE,0xDF,0x1F,0xDD,0x1D,0x1C,0xDC,0x14,0xD4, 
	0xD5,0x15,0xD7,0x17,0x16,0xD6,0xD2,0x12,0x13,0xD3, 
	0x11,0xD1,0xD0,0x10,0xF0,0x30,0x31,0xF1,0x33,0xF3, 
	0xF2,0x32,0x36,0xF6,0xF7,0x37,0xF5,0x35,0x34,0xF4, 
	0x3C,0xFC,0xFD,0x3D,0xFF,0x3F,0x3E,0xFE,0xFA,0x3A, 
	0x3B,0xFB,0x39,0xF9,0xF8,0x38,0x28,0xE8,0xE9,0x29, 
	0xEB,0x2B,0x2A,0xEA,0xEE,0x2E,0x2F,0xEF,0x2D,0xED, 
	0xEC,0x2C,0xE4,0x24,0x25,0xE5,0x27,0xE7,0xE6,0x26, 
	0x22,0xE2,0xE3,0x23,0xE1,0x21,0x20,0xE0,0xA0,0x60, 
	0x61,0xA1,0x63,0xA3,0xA2,0x62,0x66,0xA6,0xA7,0x67, 
	0xA5,0x65,0x64,0xA4,0x6C,0xAC,0xAD,0x6D,0xAF,0x6F, 
	0x6E,0xAE,0xAA,0x6A,0x6B,0xAB,0x69,0xA9,0xA8,0x68, 
	0x78,0xB8,0xB9,0x79,0xBB,0x7B,0x7A,0xBA,0xBE,0x7E, 
	0x7F,0xBF,0x7D,0xBD,0xBC,0x7C,0xB4,0x74,0x75,0xB5, 
	0x77,0xB7,0xB6,0x76,0x72,0xB2,0xB3,0x73,0xB1,0x71, 
	0x70,0xB0,0x50,0x90,0x91,0x51,0x93,0x53,0x52,0x92, 
	0x96,0x56,0x57,0x97,0x55,0x95,0x94,0x54,0x9C,0x5C, 
	0x5D,0x9D,0x5F,0x9F,0x9E,0x5E,0x5A,0x9A,0x9B,0x5B, 
	0x99,0x59,0x58,0x98,0x88,0x48,0x49,0x89,0x4B,0x8B, 
	0x8A,0x4A,0x4E,0x8E,0x8F,0x4F,0x8D,0x4D,0x4C,0x8C, 
	0x44,0x84,0x85,0x45,0x87,0x47,0x46,0x86,0x82,0x42, 
	0x43,0x83,0x41,0x81,0x80,0x40 
}; 
 
/* CRCBUF  --  Calculate CRC-16 of BUFFLEN characters in BUFF. 
			   The first character of BUFF must be nonzero.	*/ 
 
unsigned short crc(unsigned char *buff, int bufflen) 
{ 
	register unsigned int c, crc1, crc2; 
 
	crc1 = crc2 = 0; 
	while (bufflen-- > 0) { 
		crc1 = low8[c = 0xFF & (*buff++ ^ crc1)] ^ crc2; 
		crc2 = high8[c]; 
	} 
	return ((crc2 << 8) | (crc1 & 0xFF)); 
} 
#endif