//
// Returns the object held in the node that best matches our
// key.
//
internal string GetBest(BitVector key)
{
var curnode = root;
while (curnode != null)
{
if (curnode.Children == null)
return curnode.Data;
// Get the best fitting index
var bestindex = -1;
var bestlength = 0;
for (var i = 0; i < curnode.Children.Count; i++)
{
var b = curnode.Children[i].Key.LongestCommonPrefix(key);
if (b <= bestlength) continue;
bestlength = b;
bestindex = i;
}
if (bestindex == -1)
{
return curnode.Data;
}
key = key.Range(bestlength, key.Length - bestlength);
curnode = curnode.Children[bestindex];
if (key.Length == 0)
{
return curnode.Data;
}
}
return null;
}
//
// The AddAsChildren() method create a new node with key
// "key", attach a data "data" to it, and finally link it to
// the node "n".
//
private void AddAsChildren(Node n, BitVector key, string data)
{
// If "n" has no children, just add a new one
//
if (n.Children == null)
{
// initialize the list with a capacity: we save ourself
// a few ms
n.Children = new List<Node>(2) { new Node { Key = key, Data = data } };
return;
}
//
// From here, the node n already has at least 1
// children.
// Check the one that has a common prefix with our key
//(if there is none, the bestindex variable stays at -1).
var bestindex = -1;
var bestlength = 0;
for (var i = 0; i < n.Children.Count; i++)
{
var b = n.Children[i].Key.LongestCommonPrefix(key);
if (b <= bestlength) continue;
bestlength = b;
bestindex = i;
}
//
// The node n has no children that have a common prefix
// with our key, so we create a new children node and
// attach our data there.
if (bestindex == -1)
{
n.Children.Add(new Node { Key = key, Data = data });
return;
}
// There is a children node that can hold our
// data: continue our walk with this node.
Add(n.Children[bestindex], key, data);
}
internal void Add(BitVector key, string data)
{
Add(root, key, data);
}
//
// This Add method attach an object "data" to a node "n" using
// the BitVector key as path.
//
private void Add(Node n, BitVector key, string data)
{
if (n.Key == null)
{
AddAsChildren(n, key, data);
return;
}
//
// First, calculate the longest common prefix for the key
// and the BitVector stored in this node.
//
var longest = key.LongestCommonPrefix(n.Key);
//System.Diagnostics.Debug.Assert(longest != 0);
if (longest == n.Key.Length)
{
//
// If the current node is a perfect prefix of the
// key, then remove the prefix from the key, and
// we continue our walk on the children.
//
key = key.Range(longest, key.Length - longest);
AddAsChildren(n, key, data);
return;
}
//
// Here, n.Key and key share a common prefix. So we:
//
// - Create a new node with this common prefix
// held there,
//
// - make n.Key and a new node with key as
// children of this new node.
var common = n.Key.Range(0, longest);
var c1 = new Node
{
Key = n.Key.Range(longest, n.Key.Length - longest),
Data = n.Data,
Children = n.Children
};
var c2 = new Node { Key = key.Range(longest, key.Length - longest), Data = data };
n.Key = common;
n.Data = null;
// initialize the list with a capacity: we save ourself
// a few ms
n.Children = new List<Node>(2) { c1, c2 };
}
public int LongestCommonPrefix(BitVector other)
{
var i = 0;
while ((i <= other.mMaxoffset) && (i <= mMaxoffset))
{
if (other.Get(i) != Get(i))
{
return i;
}
i++;
}
return i;
}
public BitVector Range(int start, int length)
{
var result = new BitVector();
for (var i = start; i < (start + length); i++)
{
result.Set(i - start, Get(i));
}
return result;
}
private static BitVector Ip6ToBitVector(string ip)
{
var elements = ip.Split(':');
var bv = new BitVector();
// only the first three? parts are significant for geolocation
for (var index = 0; index < Math.Min(elements.Length, 3); index++)
{
var h = elements[index];
bv.AddData(
string.IsNullOrEmpty(h)
? 0
: int.Parse(h, NumberStyles.HexNumber, CultureInfo.InvariantCulture), 16);
}
return bv;
}
private static BitVector Ip4ToBitVector(string ip)
{
var elements = ip.Split('.');
var bv = new BitVector();
// only the first three bits are important
for (var index = 0; index < Math.Min(elements.Length, 3); index++)
{
var s = elements[index];
if (string.IsNullOrEmpty(s)) break;
bv.AddData(int.Parse(s, CultureInfo.InvariantCulture), 8);
}
return bv;
}
