How to convert hex string to byte array in C#

For example, Convert Hex String to Byte Array

using System;
using System.Collections.Generic;

public static class HexUtil
{
    private static readonly Dictionary<char, byte> HexMap = new Dictionary<char, byte>()
    {
        { '0', 0x0 }, { '1', 0x1 }, { '2', 0x2 }, { '3', 0x3 },
        { '4', 0x4 }, { '5', 0x5 }, { '6', 0x6 }, { '7', 0x7 },
        { '8', 0x8 }, { '9', 0x9 }, { 'A', 0xA }, { 'B', 0xB },
        { 'C', 0xC }, { 'D', 0xD }, { 'E', 0xE }, { 'F', 0xF },
        { 'a', 0xA }, { 'b', 0xB }, { 'c', 0xC }, { 'd', 0xD },
        { 'e', 0xE }, { 'f', 0xF }
    };

    public static byte[] ToBytes(this string hex)
    {
        if (string.IsNullOrWhiteSpace(hex))
            throw new ArgumentException("Hex string cannot be null or empty.");

        if (hex.Length % 2 != 0)
            throw new FormatException("Hex string must have an even number of characters.");

        bool hasPrefix = hex.StartsWith("0x", StringComparison.OrdinalIgnoreCase);
        int startIndex = hasPrefix ? 2 : 0;
        byte[] bytes = new byte[(hex.Length - startIndex) / 2];

        try
        {
            for (int i = startIndex, j = 0; i < hex.Length; i += 2, j++)
            {
                bytes[j] = (byte)((HexMap[hex[i]] << 4) | HexMap[hex[i + 1]]);
            }
            return bytes;
        }
        catch (KeyNotFoundException)
        {
            throw new FormatException("Hex string contains invalid characters.");
        }
    }
}

Usage:

using System;

class Program
{
    static void Main()
    {
        string hexString = "0x4F2A";
        byte[] byteArray = hexString.ToBytes();

        Console.WriteLine(BitConverter.ToString(byteArray)); // Output: 4F-2A
    }
}

In this example:

1. Validation Checks: Ensures the string is not empty and has an even length.
2. Handles 0x Prefix: Skips 0x if present.
3. Lookup Table: Converts characters to their hexadecimal values.
4. Bitwise Operations: Combines two half-bytes into a full byte.

This method is fast and efficient, suitable for performance-critical applications.