Most light weight conversion from hex to byte in c#? [duplicate]

Question

Possible Duplicate:
How do you convert Byte Array to Hexadecimal String, and vice versa?

I need an efficient and fast way to do this conversion. I have tried two different ways, but they are not efficient enough for me. Is there any other quick method to accomplish this in a real-time fashion for an application with huge data?

  public byte[] StringToByteArray(string hex)
    {
        return Enumerable.Range(0, hex.Length / 2).Select(x => Byte.Parse(hex.Substring(2 * x, 2), NumberStyles.HexNumber)).ToArray(); 
    }

The above one felt more efficient to me.

 public static byte[] stringTobyte(string hexString)
    {
        try
        {
            int bytesCount = (hexString.Length) / 2;
            byte[] bytes = new byte[bytesCount];
            for (int x = 0; x < bytesCount; ++x)
            {
                bytes[x] = Convert.ToByte(hexString.Substring(x * 2, 2), 16);
            }
            return bytes;
        }
        catch
        {
            throw;
        }

Answer 1

If you really need efficiency then:

• Don't create substrings
• Don't create an iterator

Or, and get rid of try blocks which only have a catch block which rethrows... for simplicity rather than efficiency though.

This would be a pretty efficient version:

public static byte[] ParseHex(string hexString)
{
    if ((hexString.Length & 1) != 0)
    {
        throw new ArgumentException("Input must have even number of characters");
    }
    int length = hexString.Length / 2;
    byte[] ret = new byte[length];
    for (int i = 0, j = 0; i < length; i++)
    {
        int high = ParseNybble(hexString[j++]);
        int low = ParseNybble(hexString[j++]);
        ret[i] = (byte) ((high << 4) | low);
    }

    return ret;
}

private static int ParseNybble(char c)
{
    // TODO: Benchmark using if statements instead
    switch (c)
    {
        case '0': case '1': case '2': case '3': case '4':
        case '5': case '6': case '7': case '8': case '9':
            return c - '0';
        case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
            return c - ('a' - 10);
        case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
            return c - ('A' - 10);
        default:
            throw new ArgumentException("Invalid nybble: " + c);
    }
    return c;
}

The TODO refers to an alternative like this. I haven't measured which is faster.

private static int ParseNybble(char c)
{
    if (c >= '0' && c <= '9')
    {
        return c - '0';
    }
    c = (char) (c & ~0x20);
    if (c >= 'A' && c <= 'F')
    {
        return c - ('A' - 10);
    }
    throw new ArgumentException("Invalid nybble: " + c);
}