c# 判斷文本文件的編碼格式

using System;
using System.IO;
using System.Text;

namespace Helper
{
    public class EncodingHelper
    {
        public static Encoding GetType(FileStream fs)
        {
            byte[] Unicode = {0xFF, 0xFE, 0x41};
            byte[] UnicodeBIG = {0xFE, 0xFF, 0x00};
            byte[] UTF8 = {0xEF, 0xBB, 0xBF}; //帶BOM 
            var reVal = Encoding.Default;

            var r = new BinaryReader(fs, Encoding.Default);
            int i;
            int.TryParse(fs.Length.ToString(), out i);
            var ss = r.ReadBytes(i);
            if (IsUTF8Bytes(ss) || ss[0] == 0xEF && ss[1] == 0xBB && ss[2] == 0xBF)
            {
                reVal = Encoding.UTF8;
            }
            else if (ss[0] == 0xFE && ss[1] == 0xFF && ss[2] == 0x00)
            {
                reVal = Encoding.BigEndianUnicode;
            }
            else if (ss[0] == 0xFF && ss[1] == 0xFE && ss[2] == 0x41)
            {
                reVal = Encoding.Unicode;
            }

            r.Close();
            return reVal;
        }

        private static bool IsUTF8Bytes(byte[] data)
        {
            var charByteCounter = 1; //計算當前正分析的字符應還有的字節數 
            byte curByte; //當前分析的字節. 
            for (var i = 0; i < data.Length; i++)
            {
                curByte = data[i];
                if (charByteCounter == 1)
                {
                    if (curByte >= 0x80)
                    {
                        //判斷當前 
                        while (((curByte <<= 1) & 0x80) != 0)
                        {
                            charByteCounter++;
                        }

                        //標記位首位若為非0 則至少以2個1開始 如:110XXXXX...........1111110X 
                        if (charByteCounter == 1 || charByteCounter > 6)
                        {
                            return false;
                        }
                    }
                }
                else
                {
                    //若是UTF-8 此時第一位必須為1 
                    if ((curByte & 0xC0) != 0x80)
                    {
                        return false;
                    }

                    charByteCounter--;
                }
            }

            if (charByteCounter > 1)
            {
                throw new Exception("非預期的byte格式");
            }

            return true;
        }
    }
}