/***************************************************************************
 *
 * PROJECT: The Dark Mod
 * $Revision$
 * $Date$
 * $Author$
 *
 ***************************************************************************/

// Copyright (C) 2004 Id Software, Inc.
//

#include "../precompiled.h"
#pragma hdrstop

static bool init_version = FileVersionList("$Id$", init_version);

/*
   CRC-8
*/

#define CRC8_INIT_VALUE		0x0000
#define CRC8_XOR_VALUE		0x0000

#ifdef CREATE_CRC_TABLE

static byte crctable[256];

/*
   Generate a table for a byte-wise 8-bit CRC calculation on the polynomial:
   x^8 + x^2 + x^1 + x^0
*/

void make_crc_table( void ) {
	int i, j;
	unsigned long poly, c;
	/* terms of polynomial defining this crc (except x^8): */
	static const byte p[] = {0,1,2};

	/* make exclusive-or pattern from polynomial (0x07) */
	poly = 0L;
	for ( i = 0; i < sizeof( p ) / sizeof( byte ); i++ ) {
		poly |= 1L << p[i];
	}

	for ( i = 0; i < 256; i++ ) {
		c = i;
		for ( j = 0; j < 8; j++ ) {
			c = ( c & 0x80 ) ? poly ^ ( c << 1 ) : ( c << 1 );
		}
		crctable[i] = (byte) c;
	}
}

#else

/*
  Table of CRC-8's of all single-byte values (made by make_crc_table)
*/
static byte crctable[256] = {
	0x00, 0x07, 0x0E, 0x09, 0x1C, 0x1B, 0x12, 0x15,
	0x38, 0x3F, 0x36, 0x31, 0x24, 0x23, 0x2A, 0x2D,
	0x70, 0x77, 0x7E, 0x79, 0x6C, 0x6B, 0x62, 0x65,
	0x48, 0x4F, 0x46, 0x41, 0x54, 0x53, 0x5A, 0x5D,
	0xE0, 0xE7, 0xEE, 0xE9, 0xFC, 0xFB, 0xF2, 0xF5,
	0xD8, 0xDF, 0xD6, 0xD1, 0xC4, 0xC3, 0xCA, 0xCD,
	0x90, 0x97, 0x9E, 0x99, 0x8C, 0x8B, 0x82, 0x85,
	0xA8, 0xAF, 0xA6, 0xA1, 0xB4, 0xB3, 0xBA, 0xBD,
	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
};

#endif

void CRC8_InitChecksum( unsigned char &crcvalue ) {
	crcvalue = CRC8_INIT_VALUE;
}

void CRC8_Update( unsigned char &crcvalue, const byte data ) {
	crcvalue = crctable[crcvalue ^ data];
}

void CRC8_UpdateChecksum( unsigned char &crcvalue, const void *data, int length ) {
	unsigned char crc;
	const unsigned char *buf = (const unsigned char *) data;

	crc = crcvalue;
	while( length-- ) {
		crc = crctable[crc ^ *buf++];
	}
	crcvalue = crc;
}

void CRC8_FinishChecksum( unsigned char &crcvalue ) {
	crcvalue ^= CRC8_XOR_VALUE;
}

unsigned char CRC8_BlockChecksum( const void *data, int length ) {
	unsigned char crc;

	CRC8_InitChecksum( crc );
	CRC8_UpdateChecksum( crc, data, length );
	CRC8_FinishChecksum( crc );
	return crc;
}