C# BitConverte擴展方法，提供基於大端模式下的數值和字節數組的相互轉換

數值轉字節數組，以及字節數組轉數值，需要注意的是C#的本地字節序是小端模式的，而網絡字節序卻是（大端模式），所以我用到了IPAddress來進行Host和Network的轉換

為了簡單以及更好的性能，做了一些取巧的處理方式，盡量避免數組拷貝和反轉，看上去很詭異，經過簡單測試貌似沒啥問題，不敢保證百分百沒問題啊，如果有問題，望指出啊，不建議直接拿來用啊

 

    /// <summary>
    /// 對BitConverter進行方法擴展
    /// </summary>
    public static class BitConverterExtend {
        /// <summary>
        /// 得到數值的網絡字節序（大端模式）的字節數組
        /// </summary> 
        public static byte[] GetBytes_Network(this short num) {
            return BitConverter.GetBytes(IPAddress.HostToNetworkOrder(num));
        }
        public static byte[] GetBytes_Network(this ushort num) {
            return ((short)num).GetBytes_Network();  //這樣比反轉數組快
        }
        public static byte[] GetBytes_Network(this int num) {
            return BitConverter.GetBytes(IPAddress.HostToNetworkOrder(num));
        }
        public static byte[] GetBytes_Network(this uint num) {
            return ((int)num).GetBytes_Network();
        }
        public static byte[] GetBytes_Network(this long num) {
            return BitConverter.GetBytes(IPAddress.HostToNetworkOrder(num));
        }
        public static byte[] GetBytes_Network(this ulong num) {
            return ((long)num).GetBytes_Network();
        }
        public static byte[] GetBytes_Network(this float num) {
            return BitConverter.GetBytes(num).Reverse().ToArray();
        }
        public static byte[] GetBytes_Network(this double num) {
            return BitConverter.GetBytes(num).Reverse().ToArray();
        }
        public static byte[] GetBytes_UTF8(this string value) {
            return Encoding.UTF8.GetBytes(value);
        }
        /// <summary>
        /// 將網絡字節序（大端模式）的字節數組轉成本地字節序（小端模式）的數值
        /// </summary> 
        public static short ToInt16_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return IPAddress.NetworkToHostOrder(BitConverter.ToInt16(networkBytes, startIndex));  //傳入引用和起始索引，減少一個數組拷貝
        }
        public static ushort ToUInt16_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return (ushort)((networkBytes[startIndex++] << 8) | networkBytes[startIndex]); //直接自己按位操作，這樣最快
        }
        public static int ToInt32_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return IPAddress.NetworkToHostOrder(BitConverter.ToInt32(networkBytes, startIndex));
        }
        public static uint ToUInt32_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return (uint)((networkBytes[startIndex++] << 24) | (networkBytes[startIndex++] << 16)
                | (networkBytes[startIndex++] << 8) | networkBytes[startIndex]);
        }
        public static long ToInt64_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return IPAddress.NetworkToHostOrder(BitConverter.ToInt64(networkBytes, startIndex));
        }
        public static ulong ToUInt64_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return (ulong)((networkBytes[startIndex++] << 56) | (networkBytes[startIndex++] << 48)
                | (networkBytes[startIndex++] << 40) | (networkBytes[startIndex++] << 32)
                | (networkBytes[startIndex++] << 24) | (networkBytes[startIndex++] << 16)
                | (networkBytes[startIndex++] << 8) | networkBytes[startIndex]);
        }
        public static float ToFloat_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return BitConverter.ToSingle(CopyAndReverse(networkBytes, startIndex, 4), 0);
        }
        /// <summary>
        /// 拷貝反轉
        /// </summary> 
        static byte[] CopyAndReverse(byte[] networkBytes, int startIndex, int len) {
            byte[] bs = new byte[len];
            for (int i = 0; i < len; i++) {
                bs[len - 1 - i] = networkBytes[startIndex + i];  //反轉拷貝
            }
            return bs;
        }
        public static double ToDouble_ByNetworkBytes(this byte[] networkBytes, int startIndex) {
            return BitConverter.ToDouble(CopyAndReverse(networkBytes, startIndex, 8), 0);
        }
        public static string GetString_UTF8(this byte[] value, int startIndex, int count) {
            return Encoding.UTF8.GetString(value, startIndex, count);
        }
    }