using System.Text;

namespace Service.Fire.Common;

public class CRC16
{
    private const ushort Polynomial = 0x1021;  
    private ushort[] crcTable = new ushort[256];  
  
    public CRC16()  
    {  
        for (int i = 0; i < 256; i++)  
        {  
            ushort value = 0;  
            ushort temp = (ushort)(i << 8);  
            for (byte j = 0; j < 8; j++)  
            {  
                if (((value ^ temp) & 0x8000) != 0)  
                {  
                    value = (ushort)((value << 1) ^ Polynomial);  
                }  
                else  
                {  
                    value = (ushort)(value << 1);  
                }  
                temp = (ushort)(temp << 1);  
            }  
            crcTable[i] = value;  
        }  
    }  
  
    public ushort ComputeChecksum(byte[] bytes)  
    {  
        ushort crc = 0xFFFF; // 初始值  
        for (int i = 0; i < bytes.Length; i++)  
        {  
            byte index = (byte)((crc ^ bytes[i]) & 0xff);  
            crc = (ushort)((crc >> 8) ^ crcTable[index]);  
        }  
        return crc;  
    }  
}