求助:演算法分析

        private void myabc(ref byte[] bytes, ref int[] abc5)
        {
            for (int num1 = 0; num1 < abc5.Length; num1++)
            {
                int num2 = bytes[abc5[num1]];
                int num3 = 0;
                for (int num4 = 0; num4 < bytes.Length; num4++)
                {
                    int num5 = num1;
                    while (num5 < abc5.Length)
                    {
                        if (abc5[num5] == num4)
                        {
                            break;
                        }
                        num5++;
                    }
                    if (num5 == abc5.Length)
                    {
                        num3 += bytes[num4];
                    }
                }
                if (((byte) (num3 % 0xff)) != num2)  //num3%255
                {
                    throw new Exception("Data Error");
                }
            }
        }

這段代碼到底實現了什麼功能,什麼時候不會拋出異常?