package com.ld.igds.protocol.bhzn.utils;

public class CRC {
	
	/*寄存器初始值*/
	private final int regInitValue;
	private int register;
    /*CRC 多项式 modbus 多项式0x8005*/ 
	private final int polynomial;
	
	public CRC() {
		this(0xffff, 0x8005);
	}
	
	public CRC(int register, int polynomial) {
		this.register = register;
		this.regInitValue = register;
		this.polynomial = Integer.reverse(polynomial)>>>Integer.numberOfLeadingZeros(polynomial);
	}
 
	private void byteCRC(byte byt) {
		register ^= (byt&0xff);
		for(int i=0; i<8; i++){
			if((register&1)==0){
				register >>= 1;
			}else{
				register = (register >> 1)^polynomial;
			}
		}
	}
	
	public synchronized int crc(byte[] byts) {
		if(null==byts||byts.length==0){
			return 0;
		}
		for(int i=0; i<byts.length; i++){
			byteCRC(byts[i]);
		}
		int retn = register;
		register = this.regInitValue;
		return retn;
	}
	
	public static void main(String[] args){
		CRC crc = new CRC();
		byte[] data = {(byte)0x81, 0x12, 0x17, (byte)0xfe};
		System.out.println(Integer.toHexString(crc.crc(data)));
		data = new byte[]{2, 7};
		System.out.println(Integer.toHexString(crc.crc(data)));
	}
	
}