From a9b4a5ea623ce31c33c2362459589ce7888137a6 Mon Sep 17 00:00:00 2001
From: Zach Brown <Zbob750@live.com>
Date: Tue, 22 Jul 2014 21:52:19 -0500
Subject: [PATCH] Fix random position generator tendency to move north west

Fixes mobs sticking to one side of pens and "migrating" to the north west constantly
Backported fix from 1.8

diff --git a/src/main/java/net/minecraft/server/RandomPositionGenerator.java b/src/main/java/net/minecraft/server/RandomPositionGenerator.java
index 9342a3f..fa20a7d 100644
--- a/src/main/java/net/minecraft/server/RandomPositionGenerator.java
+++ b/src/main/java/net/minecraft/server/RandomPositionGenerator.java
@@ -27,9 +27,11 @@ public class RandomPositionGenerator {
     private static Vec3D c(EntityCreature entitycreature, int i, int j, Vec3D vec3d) {
         Random random = entitycreature.aI();
         boolean flag = false;
-        int k = 0;
-        int l = 0;
-        int i1 = 0;
+        // PaperSpigot start - int -> double
+        double k = 0;
+        double l = 0;
+        double i1 = 0;
+        // PaperSpigot end
         float f = -99999.0F;
         boolean flag1;
 
@@ -43,22 +45,27 @@ public class RandomPositionGenerator {
         }
 
         for (int j1 = 0; j1 < 10; ++j1) {
-            int k1 = random.nextInt(2 * i) - i;
-            int l1 = random.nextInt(2 * j) - j;
-            int i2 = random.nextInt(2 * i) - i;
+            // PaperSpigot start - Even distribution and average of 0
+            int k1 = random.nextInt(2 * i + 1) - i;
+            int l1 = random.nextInt(2 * j + 1) - j;
+            int i2 = random.nextInt(2 * i + 1) - i;
+            // PaperSpigot end
 
             if (vec3d == null || (double) k1 * vec3d.a + (double) i2 * vec3d.c >= 0.0D) {
-                k1 += MathHelper.floor(entitycreature.locX);
-                l1 += MathHelper.floor(entitycreature.locY);
-                i2 += MathHelper.floor(entitycreature.locZ);
-                if (!flag1 || entitycreature.b(k1, l1, i2)) {
-                    float f1 = entitycreature.a(k1, l1, i2);
+                // PaperSpigot start - Use truncated absolute destination position for checking things
+                int k1Mod = k1 + MathHelper.floor(entitycreature.locX);
+                int l1Mod = l1 + MathHelper.floor(entitycreature.locY);
+                int i2Mod = i2 + MathHelper.floor(entitycreature.locZ);
+                if (!flag1 || entitycreature.b(k1Mod, l1Mod, i2Mod)) {
+                    float f1 = entitycreature.a(k1Mod, l1Mod, i2Mod);
 
                     if (f1 > f) {
                         f = f1;
-                        k = k1;
-                        l = l1;
-                        i1 = i2;
+                        // but then the full value to set where to move
+                        k = entitycreature.locX +  k1;
+                        l = entitycreature.locY + l1;
+                        i1 = entitycreature.locZ + i2;
+                        // PaperSpigot end
                         flag = true;
                     }
                 }
@@ -66,7 +73,7 @@ public class RandomPositionGenerator {
         }
 
         if (flag) {
-            return Vec3D.a((double) k, (double) l, (double) i1);
+            return Vec3D.a(k, l, i1); // PaperSpigot remove unnecessary cast
         } else {
             return null;
         }
-- 
1.9.1