XOR Metric Example

gistfile1.java

/**
 * Copyright 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.bitcoin.examples;

import com.google.bitcoin.core.*;

import java.util.*;
import java.net.InetAddress;
import java.net.InetSocketAddress;

public class Distance {
    public static final int K = 32;

    /** @return An integer distance between the given addresses. */
    private static final int distance(InetAddress addr1, InetAddress addr2) {
        byte[] b1 = addr1.getAddress();
        byte[] b2 = addr2.getAddress();
        
        int distance;
        distance = (b1[0] ^ b2[0]) & 0xFF;
        distance = ((b1[1] ^ b2[1]) & 0xFF) | (distance << 8);
        distance = ((b1[2] ^ b2[2]) & 0xFF) | (distance << 8);
        return ((b1[3] ^ b2[3]) & 0xFF) | (distance << 8);
    }

    public static void main(String[] args) throws Exception {
        final boolean prodNet = true;
        IrcDiscovery d = new IrcDiscovery("#bitcoin" + (prodNet ? "" : "TEST")) {
            @Override
            protected void onIRCSend(String message) {
                System.out.println("-> " + message);
            }
        };
        InetSocketAddress[] peers = d.getPeers();
        Random rand = new Random();
        InetAddress localhost = InetAddress.getByName("68.27.46.62");
        TreeMap<Integer,List<InetAddress>> distances = new TreeMap<Integer,List<InetAddress>>();
        for (InetSocketAddress peer : peers)
        {
            int bin = Integer.numberOfLeadingZeros(distance(localhost, peer.getAddress()));
            List<InetAddress> atDistance = distances.get(bin);
            if (atDistance == null)
                distances.put(bin, atDistance = new ArrayList<InetAddress>());
            if (atDistance.size() < K)
                // add to list
                atDistance.add(peer.getAddress());
            else
                // randomly replace in list
                atDistance.set(rand.nextInt(K), peer.getAddress());
        }
        System.out.println("Localhost: " + localhost);
        System.out.println("Random addresses from each bucket:");
        for (Map.Entry<Integer,List<InetAddress>> entry : distances.entrySet())
        {
            System.out.println("  Peers in bin " + entry.getKey());
            for (InetAddress addr : entry.getValue())
                System.out.println(String.format("    at 0x%08x: %s", distance(localhost, addr), addr));
        }
    }
}