package org.hwo;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;

public class ChkSum {

	public static short chksum(byte[] buffer)
	{
		return chksum(buffer, 0, buffer.length);
	}

	public static short chksum(byte[] buffer,int offset,int len)
	{
		int sum = 0,
			xor = 0;
		
		for (int n = offset; n < (offset + len); n++)
		{
			sum += buffer[n];
			xor ^= buffer[n];
		}
		
		byte[] t = new byte[12];
		ByteBuffer bb = ByteBuffer.wrap(t).order(ByteOrder.LITTLE_ENDIAN);
		bb.putInt(0, sum);
		bb.putInt(4, xor);
		bb.put(8,bb.get(0));
		bb.put(9,bb.get(4));
		
		return bb.getShort(8);
	}
}