Convert string to packed ascii byte array

PackAscii.cs

/// <summary>
/// Convert a string to packed ascii byte array
/// </summary>
/// <param name="toBePacked">ascii string to be packed</param>
/// <returns>packed ascii byte array</returns>
public static byte[] PackAscii(string toBePacked)
{
    // convert the ascii to a byte array 
    byte[] ascii = System.Text.Encoding.ASCII.GetBytes(toBePacked.PadRight(8, ' '));
    List<byte> packedAscii = new List<byte>();
    int index = 0;

    // loop through four bytes at a time and pack them into three bytes.
    for (int i = 0; i < ascii.Length; i = i + 4)
    {
        // perform the bitwise operations to truncate the 6th and 7th bit
        uint result = (uint)(((ascii[index] & 0x3F) << 18) +
                                ((ascii[index + 1] & 0x3F) << 12) +
                                ((ascii[index + 2] & 0x3F) << 6) +
                                    (ascii[index + 3] & 0x3F));

        // Convert the uint array to byte. If the bitconverter class
        // is little endian, needs to be reversed. 
        byte[] packedTemp = BitConverter.GetBytes(result);
        if (BitConverter.IsLittleEndian)
        {
            // Reverse the array and skip the first byte
            Array.Reverse(packedTemp);
            for (int k = 1; k < 4; k++)
            {
                packedAscii.Add(packedTemp[k]);
            }
        }
        else
        {
            // Not little endian so just add the first three bytes.
            for (int j = 0; j < 3; j++)
            {
                packedAscii.Add(packedTemp[j]);
            }
        }
        index += 4;
    }
    
    return packedAscii.ToArray();
 }