Function convert Hex String to BitArray C#

Question

I created the following function which will do as requested (convert HEX string to BitArray). I am not sure about the efficiency of the function, but my main problem now is that the Convert.ToInt64 function is endian specific. When this is ported over to alternate chipsets we will get different results (or exceptions). So can anyone think of an alternate way to do this conversion???

public BitArray convertHexToBitArray(string hexData)
    {
        string binary_values = "";
        BitArray binary_array;

            if (hexData.Length <= "FFFFFFFFFFFFFFFF".Length) // Max Int64
            {
                binary_values = Convert.ToString(Convert.ToInt64(hexData, 16), 2);
                binary_array = new BitArray(binary_values.Length);

                for (int i = 0; i < binary_array.Length; i++)
                {
                    if (binary_values[i] == '0')
                    {
                        binary_array[i] = false;
                    }
                    else
                    {
                        binary_array[i] = true;
                    }
                }
            }
   }

I removed most of the error / exception handling to keep this to size so plz forgive that.

Solution 1

here is a simple answer, should work with a string of any length:

public static BitArray ConvertHexToBitArray(string hexData)
{
    if (hexData == null)
        return null; // or do something else, throw, ...

    BitArray ba = new BitArray(4 * hexData.Length);
    for (int i = 0; i < hexData.Length; i++)
    {
        byte b = byte.Parse(hexData[i].ToString(), NumberStyles.HexNumber);
        for (int j = 0; j < 4; j++)
        {
            ba.Set(i * 4 + j, (b & (1 << (3 - j))) != 0);
        }
    }
    return ba;
}

Solution 2

Try this:

var int64 = Int64.Parse(hexData, NumberStyles.HexNumber);
var bytes = BitConverter.GetBytes(int64);
var bitArray = new BitArray(bytes);

Solution 3

I haven't tested this (consider it pseduo code), but it would be fast:

    public static BitArray ConvertHexToBitArray(string hex)
    {
        Guard.AssertNotNullOrEmpty(hex, "hex");
        Guard.AssertHex(hex, "hex");

        var bits = new BitArray(hex.Length * 4);

        int pos = 0;

        foreach(char c in hex)
        {
            foreach(bool flag in LookupBits(c))
            {
                bits.Set(pos, flag);
                pos++;
            }
        }

        return bits;
    }

    private static readonly Dictionary<char, List<bool>> _hexVsBits = CreateHexLookupTable();

    private static Dictionary<char, List<bool>> CreateHexLookupTable()
    {
        var hexVsBits = new Dictionary<char, List<bool>>();

        hexVsBits.Add('0', CreateBitsArray(false, false, false, false));
        hexVsBits.Add('1', CreateBitsArray(false, false, false, true));
        hexVsBits.Add('2', CreateBitsArray(false, false, true, false));
        hexVsBits.Add('3', CreateBitsArray(false, false, true, true));
        hexVsBits.Add('4', CreateBitsArray(false, true, false, false));
        hexVsBits.Add('5', CreateBitsArray(false, true, false, true));
        hexVsBits.Add('6', CreateBitsArray(false, true, true, false));
        hexVsBits.Add('7', CreateBitsArray(false, true, true, true));

        // complete hex table

        return hexVsBits;
    }

    private static List<bool> CreateBitsArray(bool msb, bool msbMinusOne, bool lsbPlusOne, bool lsb)
    {
        var bits = new List<bool>(4);

        bits.Add(msb);
        bits.Add(msbMinusOne);
        bits.Add(lsbPlusOne);
        bits.Add(lsb);

        return bits;
    }

    private static IEnumerable<bool> LookupBits(char hexValue)
    {
        return _hexVsBits[hexValue];
    }
}

And the guards:

public static class Guard
{
    public static void AssertHex(string value, string parameterName)
    {
        foreach(char entry in value)
        {
            if (!Char.IsNumber(entry))
            {
                if (entry != 'a' && entry != 'A' && entry != 'b' && entry != 'B' 
                    && entry != 'c' && entry != 'C' && entry != 'd' && entry != 'D' && entry != 'e' && entry != 'E' && entry != 'f' && entry != 'F')
                {
                    throw new ArgumentException("Not a valid hexidecimal number", parameterName);
                }
            }
        }
    }

    public static void AssertNotNullOrEmpty(string value, string parameterName)
    {
        if (string.IsNullOrEmpty(value))
            throw new ArgumentNullException(parameterName);
    }
}