Converting Hex String To Corresponding Byte Array Using C#

gistfile1.txt

// Origin: http://blogs.msdn.com/b/heikkiri/archive/2012/07/17/hex-string-to-corresponding-byte-array.aspx

void Main()
{
	var result = ConvertToByteArray("72 0B FC".Replace(" ", string.Empty));
	result.Dump();
	
	BitConverter.ToString(result).Dump();
}

private static readonly byte[] Empty = new byte[0];

public static byte[] ConvertToByteArray(string value)
{
	byte[] bytes = null;
	if (String.IsNullOrEmpty(value))
		bytes = Empty;
	else
	{
		int string_length = value.Length;
		int character_index = (value.StartsWith("0x", StringComparison.Ordinal)) ? 2 : 0; // Does the string define leading HEX indicator '0x'. Adjust starting index accordingly.               
		int number_of_characters = string_length - character_index;

		bool add_leading_zero = false;
		if (0 != (number_of_characters % 2))
		{
			add_leading_zero = true;

			number_of_characters += 1;  // Leading '0' has been striped from the string presentation.
		}

		bytes = new byte[number_of_characters / 2]; // Initialize our byte array to hold the converted string.

		int write_index = 0;
		if (add_leading_zero)
		{
			bytes[write_index++] = FromCharacterToByte(value[character_index], character_index);
			character_index += 1;
		}

		for (int read_index = character_index; read_index < value.Length; read_index += 2)
		{
			byte upper = FromCharacterToByte(value[read_index], read_index, 4);
			byte lower = FromCharacterToByte(value[read_index + 1], read_index + 1);

			bytes[write_index++] = (byte)(upper | lower);
		}
	}

	return bytes;
}

private static byte FromCharacterToByte(char character, int index, int shift = 0)
{
	byte value = (byte)character;
	if (((0x40 < value) && (0x47 > value)) || ((0x60 < value) && (0x67 > value)))
	{
		if (0x40 == (0x40 & value))
		{
			if (0x20 == (0x20 & value))
				value = (byte)(((value + 0xA) - 0x61) << shift);
			else
				value = (byte)(((value + 0xA) - 0x41) << shift);
		}
	}
	else if ((0x29 < value) && (0x40 > value))
		value = (byte)((value - 0x30) << shift);
	else
		throw new InvalidOperationException(String.Format("Character '{0}' at index '{1}' is not valid alphanumeric character.", character, index));

	return value;
}