Decode URL

/// <summary>
/// Decodes an encoded URL
/// </summary>
/// <param name="str">Input URL</param>
/// <returns>decoded URL</returns>
public static string Decode(string str)
{
    Regex hexReg = new Regex(@"%(?<value>[A-E\d]{2})");
    StringBuilder b = new StringBuilder(str);

    int offset = 0;
    MatchCollection matches = hexReg.Matches(str);

    foreach (Match m in matches)
    {
        string hexValue = m.Groups[1].Value;
        int decValue = Convert.ToInt32(hexValue, 16);
        string charValue = Char.ConvertFromUtf32(decValue);

        b.Remove(m.Index - offset, m.Length);
        b.Insert(m.Index - offset, charValue);

        offset += m.Length - charValue.Length;
    }

    return b.ToString();
}