/// <summary>
/// Looks up a key value in the trie.
/// </summary>
/// <param name="key">The key to look up.</param>
/// <returns>The best matching <see cref="BinaryTrieNode"/> in the trie.</returns>
public BinaryTrieNode FindBestMatch(Int32 key)
{
// Pick the child to investigate.
if ((key & _bit[_keyLength + 1]) == 0)
{
// If the key matches the child's key, pass on the request.
if (null != _zero)
{
if ((key ^ _zero._key) < _bit[_zero._keyLength])
{
return(_zero.FindBestMatch(key));
}
}
}
else
{
// If the key matches the child's key, pass on the request.
if (null != _one)
{
if ((key ^ _one._key) < _bit[_one._keyLength])
{
return(_one.FindBestMatch(key));
}
}
}
// If we got here, neither child was a match, so the current
// node is the best match.
return(this);
}
/// <summary>
/// Finds the best internal match for a key.
/// </summary>
/// <param name="index">
/// The index of the root <see cref="BinaryTrieNode"/> for the given key value.
/// </param>
/// <param name="key">An <see cref="Int32"/> key value.</param>
/// <returns>A reference to the <see cref="Object"/> containing the key.</returns>
protected Object FindBestMatchInternal(Int32 index, Int32 key)
{
BinaryTrieNode root = _roots[index];
if (null == root)
{
return(null);
}
return(root.FindBestMatch(key).UserData);
}
/// <summary>
/// Attempts to find the country code corresponding to a given IP address.
/// </summary>
/// <param name="address">A <see cref="String"/> value representing the IP Address</param>
/// <returns>The two letter country code corresponding to the IP address, or
/// <strong>"??"</strong> if it was not found.
/// </returns>
public String GetCountry(String address)
{
String [] parts = address.Split('.');
// The first IndexLength bits form the key into the array of root nodes.
Int32 indexBase = ((Int32.Parse(parts[0]) << 8)
+ Int32.Parse(parts[1]));
Int32 index = indexBase >> (_indexOffset - 16);
BinaryTrieNode root = base.Roots[index];
// If we don't have a root, we don't have a value.
if (null == root)
{
return(null);
}
// Calculate the full key...
Int32 key = (indexBase << 16) + (Int32.Parse(parts[2]) << 8) + Int32.Parse(parts[3]);
// ...and look it up.
return((String)root.FindBestMatch(key).UserData);
}
