Use XORShiftRNG directly

src/main/java/net/citizensnpcs/util/Util.java

@@ -1,6 +1,5 @@
 package net.citizensnpcs.util;
 
-import java.lang.reflect.Constructor;
 import java.util.Random;
 
 import net.citizensnpcs.api.event.NPCCollisionEvent;
@@ -18,15 +17,13 @@
 
 import com.google.common.base.Splitter;
 
-@SuppressWarnings("unchecked")
 public class Util {
     // Static class for small (emphasis small) utility methods
     private Util() {
     }
 
     private static final Location AT_LOCATION = new Location(null, 0, 0, 0);
     private static final Location FROM_LOCATION = new Location(null, 0, 0, 0);
-    private static Constructor<? extends Random> RNG_CONSTRUCTOR = null;
 
     public static void assumePose(LivingEntity entity, float yaw, float pitch) {
         NMS.look(entity, yaw, pitch);
@@ -66,13 +63,7 @@ public static void faceEntity(LivingEntity from, LivingEntity at) {
     }
 
     public static Random getFastRandom() {
-        try {
-            byte[] seed = new byte[20];
-            new Random().nextBytes(seed);
-            return RNG_CONSTRUCTOR.newInstance(seed);
-        } catch (Exception e) {
-            return new Random();
-        }
+        return new XORShiftRNG();
     }
 
     public static String getMinecraftVersion() {
@@ -126,15 +117,4 @@ public static boolean matchesItemInHand(Player player, String setting) {
         }
         return false;
     }
-
-    static {
-        try {
-            RNG_CONSTRUCTOR = (Constructor<? extends Random>) Class.forName("org.uncommons.maths.random.XORShiftRNG")
-                    .getConstructor(byte[].class);
-        } catch (ClassNotFoundException e) {
-        } catch (SecurityException e) {
-        } catch (NoSuchMethodException e) {
-            e.printStackTrace();
-        }
-    }
 }

src/main/java/net/citizensnpcs/util/XORShiftRNG.java

@@ -0,0 +1,139 @@
+// ============================================================================
+//   Copyright 2006-2012 Daniel W. Dyer
+//
+//   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 net.citizensnpcs.util;
+
+import java.util.Random;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * <p>
+ * Very fast pseudo random number generator. See <a href=
+ * "http://school.anhb.uwa.edu.au/personalpages/kwessen/shared/Marsaglia03.html"
+ * >this page</a> for a description. This RNG has a period of about 2^160, which
+ * is not as long as the {@link MersenneTwisterRNG} but it is faster.
+ * </p>
+ * 
+ * <p>
+ * <em>NOTE: Because instances of this class require 160-bit seeds, it is not
+ * possible to seed this RNG using the {@link #setSeed(long)} method inherited
+ * from {@link Random}.  Calls to this method will have no effect.
+ * Instead the seed must be set by a constructor.</em>
+ * </p>
+ * 
+ * @author Daniel Dyer
+ * @since 1.2
+ */
+public class XORShiftRNG extends Random {
+    // Lock to prevent concurrent modification of the RNG's internal state.
+    private final ReentrantLock lock = new ReentrantLock();
+
+    private final byte[] seed;
+
+    // Previously used an array for state but using separate fields proved to be
+    // faster.
+    private int state1;
+    private int state2;
+    private int state3;
+    private int state4;
+    private int state5;
+
+    /**
+     * Creates an RNG and seeds it with the specified seed data.
+     * 
+     * @param seed
+     *            The seed data used to initialise the RNG.
+     */
+    public XORShiftRNG() {
+        this.seed = new byte[SEED_SIZE_BYTES];
+        SEED_GENERATOR.nextBytes(seed);
+        int[] state = convertBytesToInts(seed);
+        this.state1 = state[0];
+        this.state2 = state[1];
+        this.state3 = state[2];
+        this.state4 = state[3];
+        this.state5 = state[4];
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public byte[] getSeed() {
+        return seed.clone();
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    protected int next(int bits) {
+        try {
+            lock.lock();
+            int t = (state1 ^ (state1 >> 7));
+            state1 = state2;
+            state2 = state3;
+            state3 = state4;
+            state4 = state5;
+            state5 = (state5 ^ (state5 << 6)) ^ (t ^ (t << 13));
+            int value = (state2 + state2 + 1) * state5;
+            return value >>> (32 - bits);
+        } finally {
+            lock.unlock();
+        }
+    }
+
+    // Mask for casting a byte to an int, bit-by-bit (with
+    // bitwise AND) with no special consideration for the sign bit.
+    private static final int BITWISE_BYTE_TO_INT = 0x000000FF;
+
+    private static Random SEED_GENERATOR = new Random();
+    private static final int SEED_SIZE_BYTES = 20; // Needs 5 32-bit integers.
+    private static final long serialVersionUID = -1843001897066722618L;
+
+    /**
+     * Take four bytes from the specified position in the specified block and
+     * convert them into a 32-bit int, using the big-endian convention.
+     * 
+     * @param bytes
+     *            The data to read from.
+     * @param offset
+     *            The position to start reading the 4-byte int from.
+     * @return The 32-bit integer represented by the four bytes.
+     */
+    public static int convertBytesToInt(byte[] bytes, int offset) {
+        return (BITWISE_BYTE_TO_INT & bytes[offset + 3]) | ((BITWISE_BYTE_TO_INT & bytes[offset + 2]) << 8)
+                | ((BITWISE_BYTE_TO_INT & bytes[offset + 1]) << 16) | ((BITWISE_BYTE_TO_INT & bytes[offset]) << 24);
+    }
+
+    /**
+     * Convert an array of bytes into an array of ints. 4 bytes from the input
+     * data map to a single int in the output data.
+     * 
+     * @param bytes
+     *            The data to read from.
+     * @return An array of 32-bit integers constructed from the data.
+     * @since 1.1
+     */
+    public static int[] convertBytesToInts(byte[] bytes) {
+        if (bytes.length % 4 != 0) {
+            throw new IllegalArgumentException("Number of input bytes must be a multiple of 4.");
+        }
+        int[] ints = new int[bytes.length / 4];
+        for (int i = 0; i < ints.length; i++) {
+            ints[i] = convertBytesToInt(bytes, i * 4);
+        }
+        return ints;
+    }
+}