From 8f31713f6a8ad7d012d7a9b14e7e934d7553e52a Mon Sep 17 00:00:00 2001
From: zzz <zzz@mail.i2p>
Date: Sat, 29 Oct 2011 14:05:39 +0000
Subject: [PATCH]   * CapacityCalculator: Small adjustment for XOR distance to 
    break ties and encourage closeness

---
 history.txt                                       |  2 ++
 .../router/peermanager/CapacityCalculator.java    |  3 +++
 .../net/i2p/router/peermanager/PeerProfile.java   | 15 +++++++++++++++
 3 files changed, 20 insertions(+)

diff --git a/history.txt b/history.txt
index 07af3dc81..9579fcd51 100644
--- a/history.txt
+++ b/history.txt
@@ -1,5 +1,7 @@
 2011-10-29 zzz
   * BuildHandler: Add router.buildHandlerThreads config setting
+  * CapacityCalculator: Small adjustment for XOR distance to
+    break ties and encourage closeness
   * ProfileOrganizer: Reduce min expire time
   * SSU: Limit max peers to use as introducers
 
diff --git a/router/java/src/net/i2p/router/peermanager/CapacityCalculator.java b/router/java/src/net/i2p/router/peermanager/CapacityCalculator.java
index 76a6f1b58..839674967 100644
--- a/router/java/src/net/i2p/router/peermanager/CapacityCalculator.java
+++ b/router/java/src/net/i2p/router/peermanager/CapacityCalculator.java
@@ -21,6 +21,7 @@ class CapacityCalculator {
     private static final double BONUS_NEW = 1.25;
     private static final double BONUS_ESTABLISHED = 1;
     private static final double BONUS_SAME_COUNTRY = .85;
+    private static final double BONUS_XOR = .25;
     private static final double PENALTY_UNREACHABLE = 2;
     
     public static double calc(PeerProfile profile) {
@@ -69,6 +70,8 @@ class CapacityCalculator {
         // penalize unreachable peers
         if (profile.wasUnreachable())
             capacity -= PENALTY_UNREACHABLE;
+        // a tiny tweak to break ties and encourage closeness, -.25 to +.25
+            capacity -= profile.getXORDistance() * (BONUS_XOR / 128);
 
         capacity += profile.getCapacityBonus();
         if (capacity < 0)
diff --git a/router/java/src/net/i2p/router/peermanager/PeerProfile.java b/router/java/src/net/i2p/router/peermanager/PeerProfile.java
index e21c7c383..2b57f377b 100644
--- a/router/java/src/net/i2p/router/peermanager/PeerProfile.java
+++ b/router/java/src/net/i2p/router/peermanager/PeerProfile.java
@@ -58,6 +58,7 @@ public class PeerProfile {
     private boolean _expanded;
     private boolean _expandedDB;
     private int _consecutiveShitlists;
+    private final int _distance;
     
     public PeerProfile(RouterContext context, Hash peer) {
         this(context, peer, true);
@@ -74,6 +75,11 @@ public class PeerProfile {
         // if it is false, so all need to be fixed before we can have non-expanded profiles
         if (expand)
             expandProfile();
+        Hash us = _context.routerHash();
+        if (us != null)
+            _distance = ((_peer.getData()[0] & 0xff) ^ (us.getData()[0] & 0xff)) - 127;
+        else
+            _distance = 0;
     }
     
     /** what peer is being profiled */
@@ -115,6 +121,15 @@ public class PeerProfile {
         return us != null && us.equals(_context.commSystem().getCountry(_peer));
     }
 
+    /**
+     *  For now, just a one-byte comparison
+     *  @return -127 to +128, lower is closer
+     *  @since 0.8.11
+     */
+    public int getXORDistance() {
+        return _distance;
+    }
+
     /**
      * Is this peer active at the moment (sending/receiving messages within the 
      * given period?)