package org.reprap.comms.snap;

/**
 * 
 * Represents the checksum calculation process used in SNAP which
 * is an 8 bit CRC.
 * 
 */
public class SNAPChecksum {
	
	/**
	 * 
	 */
	byte crc;
	
	/**
	 * 
	 */
	SNAPChecksum() {
		crc = 0;
	}
	
	/**
	 * Add data to the CRC computation
	 * @param data
	 * @return The data passed for convenience
	 */
	byte addData(byte data) {
		byte i = (byte)(data ^ crc);
		
		crc = 0;
		
		if((i & 1) != 0)
			crc ^= 0x5e;
		if((i & 2) != 0)
			crc ^= 0xbc;
		if((i & 4) != 0)
			crc ^= 0x61;
		if((i & 8) != 0)
			crc ^= 0xc2;
		if((i & 0x10) != 0)
			crc ^= 0x9d;
		if((i & 0x20) != 0)
			crc ^= 0x23;
		if((i & 0x40) != 0)
			crc ^= 0x46;
		if((i & 0x80) != 0)
			crc ^= 0x8c;
		return data;
	}
	
	/**
	 * @return
	 */
	byte getResult() {
		return crc;
	}
	
}