namespace AmrControl.Common
{
    public class CRCHelper
    {
        #region CRC16
        public static byte[] CRC16(byte[] data)
        {
            int len = data.Length;
            if (len > 0)
            {
                ushort crc = 0xFFFF;

                for (int i = 0; i < len; i++)
                {
                    crc = (ushort)(crc ^ (data[i]));
                    for (int j = 0; j < 8; j++)
                    {
                        crc = (crc & 1) != 0 ? (ushort)((crc >> 1) ^ 0xA001) : (ushort)(crc >> 1);
                    }
                }
                byte hi = (byte)((crc & 0xFF00) >> 8); //高位置
                byte lo = (byte)(crc & 0x00FF); //低位置

                return new byte[] { hi, lo };
            }
            return new byte[] { 0, 0 };
        }

        public static byte[] CRC16(byte[] data, int startIndex, int len)
        {
            if (len > 0 && data != null)
            {
                ushort crc = 0xFFFF;

                for (int i = startIndex; i < startIndex + len && i < data.Length; i++)
                {
                    crc = (ushort)(crc ^ (data[i]));
                    for (int j = 0; j < 8; j++)
                    {
                        crc = (crc & 1) != 0 ? (ushort)((crc >> 1) ^ 0xA001) : (ushort)(crc >> 1);
                    }
                }
                byte hi = (byte)((crc & 0xFF00) >> 8); //高位置
                byte lo = (byte)(crc & 0x00FF); //低位置

                return new byte[] { hi, lo };
            }
            return new byte[] { 0, 0 };
        }
        #endregion
    }
}