Question

In C#, is there a way to right/left shift an entire byte array (and subsequently adding a byte to a particular side for the last bit isn’t lost)?

I know this sounds like a weird request, but I’d still like to know if its possible and/or how to begin doing it.

Answer 1

Yes, you can. See the following methods I wrote:

/// <summary>
/// Rotates the bits in an array of bytes to the left.
/// </summary>
/// <param name="bytes">The byte array to rotate.</param>
public static void RotateLeft(byte[] bytes)
{
    bool carryFlag = ShiftLeft(bytes);

    if (carryFlag == true)
    {
        bytes[bytes.Length - 1] = (byte)(bytes[bytes.Length - 1] | 0x01);
    }
}

/// <summary>
/// Rotates the bits in an array of bytes to the right.
/// </summary>
/// <param name="bytes">The byte array to rotate.</param>
public static void RotateRight(byte[] bytes)
{
    bool carryFlag = ShiftRight(bytes);

    if (carryFlag == true)
    {
        bytes[0] = (byte)(bytes[0] | 0x80);
    }
}

/// <summary>
/// Shifts the bits in an array of bytes to the left.
/// </summary>
/// <param name="bytes">The byte array to shift.</param>
public static bool ShiftLeft(byte[] bytes)
{
    bool leftMostCarryFlag = false;

    // Iterate through the elements of the array from left to right.
    for (int index = 0; index < bytes.Length; index++)
    {
        // If the leftmost bit of the current byte is 1 then we have a carry.
        bool carryFlag = (bytes[index] & 0x80) > 0;

        if (index > 0)
        {
            if (carryFlag == true)
            {
                // Apply the carry to the rightmost bit of the current bytes neighbor to the left.
                bytes[index - 1] = (byte)(bytes[index - 1] | 0x01);
            }
        }
        else
        {
            leftMostCarryFlag = carryFlag;
        }

        bytes[index] = (byte)(bytes[index] << 1);
    }

    return leftMostCarryFlag;
}

/// <summary>
/// Shifts the bits in an array of bytes to the right.
/// </summary>
/// <param name="bytes">The byte array to shift.</param>
public static bool ShiftRight(byte[] bytes) 
{
    bool rightMostCarryFlag = false;
    int rightEnd = bytes.Length - 1;

    // Iterate through the elements of the array right to left.
    for (int index = rightEnd; index >= 0; index--)
    {
        // If the rightmost bit of the current byte is 1 then we have a carry.
        bool carryFlag = (bytes[index] & 0x01) > 0;

        if (index < rightEnd)
        {
            if (carryFlag == true)
            {
                // Apply the carry to the leftmost bit of the current bytes neighbor to the right.
                bytes[index + 1] = (byte)(bytes[index + 1] | 0x80);
            }
        }
        else
        {
            rightMostCarryFlag = carryFlag;
        }

        bytes[index] = (byte)(bytes[index] >> 1);
    }

    return rightMostCarryFlag;
}