Question

I would like to know how to manipulate bits from a ByteArray.
What I need is to shift the bits according to a ‘table’ that I have.

Table:

Bit 0 -> Bit 26
Bit 1 -> Bit 31
Bit 2 -> Bit 17
...
Bit 31 -> Bit 5

I convert the ByteArray to BitArray using this method

public static BitArray ByteArraytoBitArray(byte[] bytes)
{
    BitArray bits = new BitArray(bytes);
    return bits;
}

But I am stuck there, I don’t know how to shift the bits according to the table and then back to ByteArray.

EDIT:

Code Snipet:

public static byte[] StringToByteArray(String hex)
{
    int NumberChars = hex.Length;
    byte[] bytes = new byte[NumberChars / 2];
    for (int i = 0; i < NumberChars; i += 2)
        bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);
    return bytes;
}
private void button3_Click(object sender, EventArgs e)
{
    string featherearring = "00804804A02A1CA20100000000000000D2F8B6FABBB700000000000000000000";
    var strarray = StringToByteArray(featherearring);

    byte[] strarray_comp = Enc.Encrypt(strarray);

    string conv = BitConverter.ToString(strarray_comp);
    MessageBox.Show(conv.Replace("-", ""));
}



public static byte[] BitArrayToByteArray(BitArray bits)
{
    byte[] bytes = new byte[bits.Length / 8];
    bits.CopyTo(bytes, 0);
    return bytes;
}
public static byte[] Encrypt(byte[] input)
{
    BitArray source = new BitArray(input);
    BitArray target = new BitArray(source.Length);

    target[26] = source[0];
    target[31] = source[1];
    target[17] = source[2];
    target[10] = source[3];
    target[30] = source[4];
    target[16] = source[5];
    target[24] = source[6];
    target[2] = source[7];
    target[29] = source[8];
    target[8] = source[9];
    target[20] = source[10];
    target[15] = source[11];
    target[28] = source[12];
    target[11] = source[13];
    target[13] = source[14];
    target[4] = source[15];
    target[19] = source[16];
    target[23] = source[17];
    target[0] = source[18];
    target[12] = source[19];
    target[14] = source[20];
    target[27] = source[21];
    target[6] = source[22];
    target[18] = source[23];
    target[21] = source[24];
    target[3] = source[25];
    target[9] = source[26];
    target[7] = source[27];
    target[22] = source[28];
    target[1] = source[29];
    target[25] = source[30];
    target[5] = source[31];

    return BitArrayToByteArray(target);
}

my input byte array is “00804804A02A1CA20100000000000000D2F8B6FABBB700000000000000000000” and my output with zimdanen’s code is “5012000000000000000000000000000000000000000000000000000000000000” and it should be “501200002FD901000000000400000000BFE8C4DB140D11F40000000000000000”
As you can see, it gets the first 2 bytes right, but the rest is are all null.

Answer 1

Does it need to be in place? You can create a new BitArray and just copy the bits over:

BitArray source = new BitArray(bytes);

// Create target array.
BitArray target = new BitArray(source.Length);

// Map bits.
// ...
target[26] = source[0];
// ...

Or, depending on how you want to maintain your mapping “table”, you can do it like this:

// Setup mapping - <source, target>.
Dictionary<int, int> mapping = new Dictionary<int, int>();
// ...
mapping.Add(0, 26);
// ...

BitArray source = new BitArray(bytes);

// Create target array.
BitArray target = new BitArray(source.Length);

// Map bits.
foreach (int sourceIndex in mapping.Keys)
{
    int targetIndex = mapping[sourceIndex];
    target[targetIndex] = source[sourceIndex];
}