From fc21b41afb93c197b8c371490c12bb1e87b72c87 Mon Sep 17 00:00:00 2001
From: Sam Harwell <sam@tunnelvisionlabs.com>
Date: Sun, 5 May 2013 13:24:19 -0500
Subject: [PATCH 1/2] Update PredictionContext to use the MurmurHash 3 hash
 algorithm

---
 .../runtime/atn/ArrayPredictionContext.java   |  43 -------
 .../v4/runtime/atn/PredictionContext.java     |  58 ++++++++-
 .../atn/SingletonPredictionContext.java       |   3 +-
 .../org/antlr/v4/runtime/misc/MurmurHash.java | 119 ++++++++++++++++++
 4 files changed, 175 insertions(+), 48 deletions(-)
 create mode 100644 runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java

diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
index 0d1835649..60dd4303d 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ArrayPredictionContext.java
@@ -58,49 +58,6 @@ public class ArrayPredictionContext extends PredictionContext {
 		this.returnStates = returnStates;
 	}
 
-//ArrayPredictionContext(@NotNull PredictionContext[] parents, int[] returnStates, int parentHashCode, int returnStateHashCode) {
-//		super(calculateHashCode(parentHashCode, returnStateHashCode));
-//		assert parents.length == returnStates.length;
-//		assert returnStates.length > 1 || returnStates[0] != EMPTY_FULL_STATE_KEY : "Should be using PredictionContext.EMPTY instead.";
-//
-//		this.parents = parents;
-//		this.returnStates = returnStates;
-//	}
-//
-//ArrayPredictionContext(@NotNull PredictionContext[] parents, int[] returnStates, int hashCode) {
-//		super(hashCode);
-//		assert parents.length == returnStates.length;
-//		assert returnStates.length > 1 || returnStates[0] != EMPTY_FULL_STATE_KEY : "Should be using PredictionContext.EMPTY instead.";
-//
-//		this.parents = parents;
-//		this.returnStates = returnStates;
-//	}
-
-	protected static int calculateHashCode(PredictionContext[] parents, int[] returnStates) {
-		return calculateHashCode(calculateParentHashCode(parents),
-								 calculateReturnStatesHashCode(returnStates));
-	}
-
-	protected static int calculateParentHashCode(PredictionContext[] parents) {
-		int hashCode = 1;
-		for (PredictionContext p : parents) {
-			if ( p!=null ) { // can be null for full ctx stack in ArrayPredictionContext
-				hashCode = hashCode * 31 ^ p.hashCode();
-			}
-		}
-
-		return hashCode;
-	}
-
-	protected static int calculateReturnStatesHashCode(int[] returnStates) {
-		int hashCode = 1;
-		for (int state : returnStates) {
-			hashCode = hashCode * 31 ^ state;
-		}
-
-		return hashCode;
-	}
-
 	@Override
 	public Iterator<SingletonPredictionContext> iterator() {
 		return new Iterator<SingletonPredictionContext>() {
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
index b8b7a7d3e..c93088b5f 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionContext.java
@@ -33,6 +33,7 @@ package org.antlr.v4.runtime.atn;
 import org.antlr.v4.runtime.Recognizer;
 import org.antlr.v4.runtime.RuleContext;
 import org.antlr.v4.runtime.misc.DoubleKeyMap;
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.antlr.v4.runtime.misc.Nullable;
 
@@ -61,9 +62,32 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 	 */
 	public static final int EMPTY_RETURN_STATE = Integer.MAX_VALUE;
 
+	private static final int INITIAL_HASH = 1;
+
 	public static int globalNodeCount = 0;
 	public final int id = globalNodeCount++;
 
+	/**
+	 * Stores the computed hash code of this {@link PredictionContext}. The hash
+	 * code is computed in parts to match the following reference algorithm.
+	 *
+	 * <pre>
+	 *  private int referenceHashCode() {
+	 *      int hash = {@link MurmurHash#initialize}({@link #INITIAL_HASH});
+	 *
+	 *      for (int i = 0; i < {@link #size()}; i++) {
+	 *          hash = {@link MurmurHash#update}(hash, {@link #getParent}(i));
+	 *      }
+	 *
+	 *      for (int i = 0; i < {@link #size()}; i++) {
+	 *          hash = {@link MurmurHash#update}(hash, {@link #getReturnState}(i));
+	 *      }
+	 *
+	 *      hash = {@link MurmurHash#finish}(hash, 2 * {@link #size()});
+	 *      return hash;
+	 *  }
+	 * </pre>
+	 */
 	public final int cachedHashCode;
 
 	protected PredictionContext(int cachedHashCode) {
@@ -117,12 +141,40 @@ public abstract class PredictionContext implements Iterable<SingletonPredictionC
 	}
 
 	@Override
-	public int hashCode() {
+	public final int hashCode() {
 		return cachedHashCode;
 	}
 
-	protected static int calculateHashCode(int parentHashCode, int returnStateHashCode) {
-		return 5 * 5 * 7 + 5 * parentHashCode + returnStateHashCode;
+	@Override
+	public abstract boolean equals(Object obj);
+
+	protected static int calculateEmptyHashCode() {
+		int hash = MurmurHash.initialize(INITIAL_HASH);
+		hash = MurmurHash.finish(hash, 0);
+		return hash;
+	}
+
+	protected static int calculateHashCode(PredictionContext parent, int returnState) {
+		int hash = MurmurHash.initialize(INITIAL_HASH);
+		hash = MurmurHash.update(hash, parent);
+		hash = MurmurHash.update(hash, returnState);
+		hash = MurmurHash.finish(hash, 2);
+		return hash;
+	}
+
+	protected static int calculateHashCode(PredictionContext[] parents, int[] returnStates) {
+		int hash = MurmurHash.initialize(INITIAL_HASH);
+
+		for (PredictionContext parent : parents) {
+			hash = MurmurHash.update(hash, parent);
+		}
+
+		for (int returnState : returnStates) {
+			hash = MurmurHash.update(hash, returnState);
+		}
+
+		hash = MurmurHash.finish(hash, 2 * parents.length);
+		return hash;
 	}
 
 	// dispatch
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
index b53113c00..3cf538b84 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/SingletonPredictionContext.java
@@ -37,8 +37,7 @@ public class SingletonPredictionContext extends PredictionContext {
 	public final int returnState;
 
 	SingletonPredictionContext(PredictionContext parent, int returnState) {
-		super(calculateHashCode(parent!=null ? 31 ^ parent.hashCode() : 1,
-								31 ^ returnState));
+		super(parent != null ? calculateHashCode(parent, returnState) : calculateEmptyHashCode());
 		assert returnState!=ATNState.INVALID_STATE_NUMBER;
 		this.parent = parent;
 		this.returnState = returnState;
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java b/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java
new file mode 100644
index 000000000..c429092b7
--- /dev/null
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java
@@ -0,0 +1,119 @@
+/*
+ * [The "BSD license"]
+ *  Copyright (c) 2012 Terence Parr
+ *  Copyright (c) 2012 Sam Harwell
+ *  All rights reserved.
+ *
+ *  Redistribution and use in source and binary forms, with or without
+ *  modification, are permitted provided that the following conditions
+ *  are met:
+ *
+ *  1. Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ *  2. Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *  3. The name of the author may not be used to endorse or promote products
+ *     derived from this software without specific prior written permission.
+ *
+ *  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ *  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ *  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ *  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ *  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ *  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ *  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package org.antlr.v4.runtime.misc;
+
+/**
+ *
+ * @author Sam Harwell
+ */
+public final class MurmurHash {
+
+	private static final int DEFAULT_SEED = 0;
+
+	/**
+	 * Initialize the hash using the default seed value.
+	 *
+	 * @return the intermediate hash value
+	 */
+	public static int initialize() {
+		return initialize(DEFAULT_SEED);
+	}
+
+	/**
+	 * Initialize the hash using the specified {@code seed}.
+	 *
+	 * @param seed the seed
+	 * @return the intermediate hash value
+	 */
+	public static int initialize(int seed) {
+		return seed;
+	}
+
+	/**
+	 * Update the intermediate hash value for the next input {@code value}.
+	 *
+	 * @param hash the intermediate hash value
+	 * @param value the value to add to the current hash
+	 * @return the updated intermediate hash value
+	 */
+	public static int update(int hash, int value) {
+		final int c1 = 0xCC9E2D51;
+		final int c2 = 0x1B873593;
+		final int r1 = 15;
+		final int r2 = 13;
+		final int m = 5;
+		final int n = 0xE6546B64;
+
+		int k = value;
+		k = k * c1;
+		k = (k << r1) | (k >>> (32 - r1));
+		k = k * c2;
+
+		hash = hash ^ k;
+		hash = (hash << r2) | (hash >>> (32 - r2));
+		hash = hash * m + n;
+
+		return hash;
+	}
+
+	/**
+	 * Update the intermediate hash value for the next input {@code value}.
+	 *
+	 * @param hash the intermediate hash value
+	 * @param value the value to add to the current hash
+	 * @return the updated intermediate hash value
+	 */
+	public static int update(int hash, Object value) {
+		return update(hash, value != null ? value.hashCode() : 0);
+	}
+
+	/**
+	 * Apply the final computation steps to the intermediate value {@code hash}
+	 * to form the final result of the MurmurHash 3 hash function.
+	 *
+	 * @param hash the intermediate hash value
+	 * @param numberOfWords the number of integer values added to the hash
+	 * @return the final hash result
+	 */
+	public static int finish(int hash, int numberOfWords) {
+		hash = hash ^ (numberOfWords * 4);
+		hash = hash ^ (hash >>> 16);
+		hash = hash * 0x85EBCA6B;
+		hash = hash ^ (hash >>> 13);
+		hash = hash * 0xC2B2AE35;
+		hash = hash ^ (hash >>> 16);
+		return hash;
+	}
+
+	private MurmurHash() {
+	}
+
+}

From d67d924b0d36a4f84494b79abbb000833749f130 Mon Sep 17 00:00:00 2001
From: Sam Harwell <sam@tunnelvisionlabs.com>
Date: Sun, 5 May 2013 14:03:48 -0500
Subject: [PATCH 2/2] Update additional classes to use MurmurHash hashing

---
 .../org/antlr/v4/runtime/atn/ATNConfig.java   | 16 ++++++++-------
 .../antlr/v4/runtime/atn/LexerATNConfig.java  | 10 ++++++++--
 .../antlr/v4/runtime/atn/PredictionMode.java  |  9 +++++----
 .../antlr/v4/runtime/atn/SemanticContext.java | 14 +++++++------
 .../org/antlr/v4/runtime/dfa/DFAState.java    | 10 +++++-----
 .../antlr/v4/runtime/misc/Array2DHashSet.java |  8 +++++---
 .../v4/runtime/misc/FlexibleHashMap.java      |  8 +++++---
 .../antlr/v4/runtime/misc/IntervalSet.java    | 13 +++++++-----
 .../org/antlr/v4/runtime/misc/MurmurHash.java | 20 ++++++++++++++++++-
 .../codegen/model/decl/ContextGetterDecl.java |  7 ++++++-
 10 files changed, 78 insertions(+), 37 deletions(-)

diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfig.java b/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfig.java
index 0e5b3ddfa..95af660e5 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfig.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/ATNConfig.java
@@ -31,6 +31,7 @@
 package org.antlr.v4.runtime.atn;
 
 import org.antlr.v4.runtime.Recognizer;
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.antlr.v4.runtime.misc.Nullable;
 
@@ -159,13 +160,14 @@ public class ATNConfig {
 
 	@Override
 	public int hashCode() {
-		int hashCode = 7;
-		hashCode = 5 * hashCode + state.stateNumber;
-		hashCode = 5 * hashCode + alt;
-		hashCode = 5 * hashCode + (context != null ? context.hashCode() : 0);
-		hashCode = 5 * hashCode + semanticContext.hashCode();
-        return hashCode;
-    }
+		int hashCode = MurmurHash.initialize(7);
+		hashCode = MurmurHash.update(hashCode, state.stateNumber);
+		hashCode = MurmurHash.update(hashCode, alt);
+		hashCode = MurmurHash.update(hashCode, context);
+		hashCode = MurmurHash.update(hashCode, semanticContext);
+		hashCode = MurmurHash.finish(hashCode, 4);
+		return hashCode;
+	}
 
 	@Override
 	public String toString() {
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNConfig.java b/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNConfig.java
index 368eebc7c..8cd79cabf 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNConfig.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/LexerATNConfig.java
@@ -30,6 +30,7 @@
 
 package org.antlr.v4.runtime.atn;
 
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.antlr.v4.runtime.misc.Nullable;
 
@@ -84,8 +85,13 @@ public class LexerATNConfig extends ATNConfig {
 
 	@Override
 	public int hashCode() {
-		int hashCode = super.hashCode();
-		hashCode = 35 * hashCode ^ (passedThroughNonGreedyDecision ? 1 : 0);
+		int hashCode = MurmurHash.initialize(7);
+		hashCode = MurmurHash.update(hashCode, state.stateNumber);
+		hashCode = MurmurHash.update(hashCode, alt);
+		hashCode = MurmurHash.update(hashCode, context);
+		hashCode = MurmurHash.update(hashCode, semanticContext);
+		hashCode = MurmurHash.update(hashCode, passedThroughNonGreedyDecision ? 1 : 0);
+		hashCode = MurmurHash.finish(hashCode, 5);
 		return hashCode;
 	}
 
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java
index dbcecd6f0..246f55d11 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/PredictionMode.java
@@ -32,6 +32,7 @@ package org.antlr.v4.runtime.atn;
 
 import org.antlr.v4.runtime.misc.AbstractEqualityComparator;
 import org.antlr.v4.runtime.misc.FlexibleHashMap;
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 
 import java.util.BitSet;
@@ -79,9 +80,10 @@ public enum PredictionMode {
 		/** Code is function of (s, _, ctx, _) */
 		@Override
 		public int hashCode(ATNConfig o) {
-			int hashCode = 7;
-			hashCode = 31 * hashCode + o.state.stateNumber;
-			hashCode = 31 * hashCode + o.context.hashCode();
+			int hashCode = MurmurHash.initialize(7);
+			hashCode = MurmurHash.update(hashCode, o.state.stateNumber);
+			hashCode = MurmurHash.update(hashCode, o.context);
+			hashCode = MurmurHash.finish(hashCode, 2);
 	        return hashCode;
 		}
 
@@ -89,7 +91,6 @@ public enum PredictionMode {
 		public boolean equals(ATNConfig a, ATNConfig b) {
 			if ( a==b ) return true;
 			if ( a==null || b==null ) return false;
-			if ( hashCode(a) != hashCode(b) ) return false;
 			return a.state.stateNumber==b.state.stateNumber
 				&& a.context.equals(b.context);
 		}
diff --git a/runtime/Java/src/org/antlr/v4/runtime/atn/SemanticContext.java b/runtime/Java/src/org/antlr/v4/runtime/atn/SemanticContext.java
index 3bc10ab48..40f4c898f 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/atn/SemanticContext.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/atn/SemanticContext.java
@@ -32,6 +32,7 @@ package org.antlr.v4.runtime.atn;
 
 import org.antlr.v4.runtime.Recognizer;
 import org.antlr.v4.runtime.RuleContext;
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.antlr.v4.runtime.misc.Utils;
 
@@ -91,10 +92,11 @@ public abstract class SemanticContext {
 
 		@Override
 		public int hashCode() {
-			int hashCode = 1;
-			hashCode = 31 * hashCode + ruleIndex;
-			hashCode = 31 * hashCode + predIndex;
-			hashCode = 31 * hashCode + (isCtxDependent ? 1 : 0);
+			int hashCode = MurmurHash.initialize();
+			hashCode = MurmurHash.update(hashCode, ruleIndex);
+			hashCode = MurmurHash.update(hashCode, predIndex);
+			hashCode = MurmurHash.update(hashCode, isCtxDependent ? 1 : 0);
+			hashCode = MurmurHash.finish(hashCode, 3);
 			return hashCode;
 		}
 
@@ -137,7 +139,7 @@ public abstract class SemanticContext {
 
 		@Override
 		public int hashCode() {
-			return Arrays.hashCode(opnds);
+			return MurmurHash.hashCode(opnds, AND.class.hashCode());
 		}
 
 		@Override
@@ -177,7 +179,7 @@ public abstract class SemanticContext {
 
 		@Override
 		public int hashCode() {
-			return Arrays.hashCode(opnds) + 1; // differ from AND slightly
+			return MurmurHash.hashCode(opnds, OR.class.hashCode());
 		}
 
 		@Override
diff --git a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
index 5cd35e58b..4cf7579d1 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/dfa/DFAState.java
@@ -36,6 +36,7 @@ import org.antlr.v4.runtime.atn.ATNConfig;
 import org.antlr.v4.runtime.atn.ATNConfigSet;
 import org.antlr.v4.runtime.atn.ParserATNSimulator;
 import org.antlr.v4.runtime.atn.SemanticContext;
+import org.antlr.v4.runtime.misc.MurmurHash;
 import org.antlr.v4.runtime.misc.NotNull;
 import org.antlr.v4.runtime.misc.Nullable;
 
@@ -150,11 +151,10 @@ public class DFAState {
 
 	@Override
 	public int hashCode() {
-		int h = 7;
-		if ( configs!=null ) {
-			h = h * 31 ^ configs.hashCode();
-		}
-		return h;
+		int hash = MurmurHash.initialize(7);
+		hash = MurmurHash.update(hash, configs.hashCode());
+		hash = MurmurHash.finish(hash, 1);
+		return hash;
 	}
 
 	/**
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java b/runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java
index 3c3cc4f6c..49ebd1ced 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java
@@ -136,15 +136,17 @@ public class Array2DHashSet<T> implements Set<T> {
 
 	@Override
 	public int hashCode() {
-		int h = 0;
+		int hash = MurmurHash.initialize();
 		for (T[] bucket : buckets) {
 			if ( bucket==null ) continue;
 			for (T o : bucket) {
 				if ( o==null ) break;
-				h += comparator.hashCode(o);
+				hash = MurmurHash.update(hash, comparator.hashCode(o));
 			}
 		}
-		return h;
+
+		hash = MurmurHash.finish(hash, size());
+		return hash;
 	}
 
 	@Override
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/FlexibleHashMap.java b/runtime/Java/src/org/antlr/v4/runtime/misc/FlexibleHashMap.java
index ae24920ec..7f9e86898 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/FlexibleHashMap.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/FlexibleHashMap.java
@@ -183,15 +183,17 @@ public class FlexibleHashMap<K,V> implements Map<K, V> {
 
 	@Override
 	public int hashCode() {
-		int h = 0;
+		int hash = MurmurHash.initialize();
 		for (LinkedList<Entry<K, V>> bucket : buckets) {
 			if ( bucket==null ) continue;
 			for (Entry<K, V> e : bucket) {
 				if ( e==null ) break;
-				h += comparator.hashCode(e.key);
+				hash = MurmurHash.update(hash, comparator.hashCode(e.key));
 			}
 		}
-		return h;
+
+		hash = MurmurHash.finish(hash, size());
+		return hash;
 	}
 
 	@Override
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java b/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
index 58a2144b0..007680fe1 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/IntervalSet.java
@@ -424,11 +424,14 @@ public class IntervalSet implements IntSet {
 
 	@Override
 	public int hashCode() {
-		if ( isNil() ) return 0;
-		int n = 0;
-		// just add left edge of intervals
-		for (Interval I : intervals) n += I.a;
-		return n;
+		int hash = MurmurHash.initialize();
+		for (Interval I : intervals) {
+			hash = MurmurHash.update(hash, I.a);
+			hash = MurmurHash.update(hash, I.b);
+		}
+
+		hash = MurmurHash.finish(hash, intervals.size() * 2);
+		return hash;
 	}
 
 	/** Are two IntervalSets equal?  Because all intervals are sorted
diff --git a/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java b/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java
index c429092b7..4d5d0ea66 100644
--- a/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java
+++ b/runtime/Java/src/org/antlr/v4/runtime/misc/MurmurHash.java
@@ -113,7 +113,25 @@ public final class MurmurHash {
 		return hash;
 	}
 
-	private MurmurHash() {
+	/**
+	 * Utility function to compute the hash code of an array using the
+	 * MurmurHash algorithm.
+	 *
+	 * @param <T> the array element type
+	 * @param data the array data
+	 * @param seed the seed for the MurmurHash algorithm
+	 * @return the hash code of the data
+	 */
+	public static <T> int hashCode(T[] data, int seed) {
+		int hash = initialize(seed);
+		for (T value : data) {
+			hash = update(hash, value);
+		}
+
+		hash = finish(hash, data.length);
+		return hash;
 	}
 
+	private MurmurHash() {
+	}
 }
diff --git a/tool/src/org/antlr/v4/codegen/model/decl/ContextGetterDecl.java b/tool/src/org/antlr/v4/codegen/model/decl/ContextGetterDecl.java
index 3977e0c16..99ceef298 100644
--- a/tool/src/org/antlr/v4/codegen/model/decl/ContextGetterDecl.java
+++ b/tool/src/org/antlr/v4/codegen/model/decl/ContextGetterDecl.java
@@ -31,6 +31,7 @@
 package org.antlr.v4.codegen.model.decl;
 
 import org.antlr.v4.codegen.OutputModelFactory;
+import org.antlr.v4.runtime.misc.MurmurHash;
 
 public abstract class ContextGetterDecl extends Decl {
 	public ContextGetterDecl(OutputModelFactory factory, String name) {
@@ -44,7 +45,11 @@ public abstract class ContextGetterDecl extends Decl {
 
 	@Override
 	public int hashCode() {
-		return name.hashCode() + getArgType().hashCode();
+		int hash = MurmurHash.initialize();
+		hash = MurmurHash.update(hash, name);
+		hash = MurmurHash.update(hash, getArgType());
+		hash = MurmurHash.finish(hash, 2);
+		return hash;
 	}
 
 	/** Make sure that a getter does not equal a label. X() and X are ok.