在C#中實現BigEndian的數字

在我們的PC機中，C#的數字是LittleEndian的，導致在做網路通訊協定和和檔案解析時有許多不便，因此，我寫了個BigEndian的數位類，這裡記錄一下，以後還會經常用到。

    static class BigEndianUIntHelper
    {
        public static uint ToUInt32(byte[] data)
        {
            Contract.Assume(data.Length <= 4);
            return BitConverter.ToUInt32(new byte[4 - data.Length].Concat(data).Reverse().ToArray(), 0);
        }

        public static byte[] ToBytes(uint num, int size)
        {
            Contract.Assume(size <= 4);
            return BitConverter.GetBytes(num).Take(size).Reverse().ToArray();
        }
    }

    [StructLayout(LayoutKind.Sequential)]
    struct BigEndianUInt24
    {
        const int size = 3;

        [MarshalAs(UnmanagedType.ByValArray, SizeConst = size)]
        byte[] data;

        public static implicit operator uint(BigEndianUInt24 d) { return BigEndianUIntHelper.ToUInt32(d.data); }
        public static implicit operator BigEndianUInt24(uint d) { return new BigEndianUInt24() { data = BigEndianUIntHelper.ToBytes(d, size) }; }
        public override string ToString() { return ((uint)this).ToString(); }
    }

    [StructLayout(LayoutKind.Sequential)]
    struct BigEndianUInt32
    {
        const int size = 4;

        [MarshalAs(UnmanagedType.ByValArray, SizeConst = size)]
        byte[] data;

        public static implicit operator uint(BigEndianUInt32 d) { return BigEndianUIntHelper.ToUInt32(d.data); }
        public static implicit operator BigEndianUInt32(uint d) { return new BigEndianUInt32 { data = BigEndianUIntHelper.ToBytes(d, size) }; }
        public override string ToString() { return ((uint)this).ToString(); }
    }

其實這裡BigEndianUIntHelper的兩個函數應該最佳化一下的，這裡為了圖簡單，就直接用BitConverter的現成方法了。以後有需要再弄好了。

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