Reduce size of _serializedATN by adding 2 to each element: new representation avoids embedded values 0 and 0xFFFF which are common and have multi-byte representations in Java's modified UTF-8

CHANGES.txt

@@ -8,6 +8,9 @@ January 11, 2013
 * Add error 144: multi-character literals are not allowed in lexer sets
 * Error 134 now only applies to rule references in lexer sets
 * Updated error messages (cleanup)
+* Reduce size of _serializedATN by adding 2 to each element: new representation
+  avoids embedded values 0 and 0xFFFF which are common and have multi-byte
+  representations in Java's modified UTF-8
 
 January 10, 2013
 

runtime/Java/src/org/antlr/v4/runtime/atn/ATNSimulator.java

@@ -43,7 +43,7 @@ import java.util.List;
 public abstract class ATNSimulator {
 	public static final int SERIALIZED_VERSION;
 	static {
-		SERIALIZED_VERSION = 1;
+		SERIALIZED_VERSION = 2;
 	}
 
 	/** Must distinguish between missing edge and edge we know leads nowhere */
@@ -99,6 +99,12 @@ public abstract class ATNSimulator {
 	}
 
 	public static ATN deserialize(@NotNull char[] data) {
+		data = data.clone();
+		// don't adjust the first value since that's the version number
+		for (int i = 1; i < data.length; i++) {
+			data[i] = (char)(data[i] - 2);
+		}
+
 		ATN atn = new ATN();
 		List<IntervalSet> sets = new ArrayList<IntervalSet>();
 		int p = 0;

tool/src/org/antlr/v4/automata/ATNSerializer.java

@@ -53,6 +53,7 @@ import org.antlr.v4.tool.Rule;
 
 import java.io.InvalidClassException;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 public class ATNSerializer {
@@ -254,10 +255,28 @@ public class ATNSerializer {
 		for (DecisionState decStartState : atn.decisionToState) {
 			data.add(decStartState.stateNumber);
 		}
+
+		// don't adjust the first value since that's the version number
+		for (int i = 1; i < data.size(); i++) {
+			assert data.get(i) >= -1 && data.get(i) < 0xFFFF;
+			int value = (data.get(i) + 2) & 0xFFFF;
+			if (value == 0xFFFF) {
+				value = -1;
+			}
+
+			data.set(i, value);
+		}
+
 		return data;
 	}
 
 	public String decode(char[] data) {
+		data = data.clone();
+		// don't adjust the first value since that's the version number
+		for (int i = 1; i < data.length; i++) {
+			data[i] = (char)(data[i] - 2);
+		}
+
 		StringBuilder buf = new StringBuilder();
 		int p = 0;
 		int version = ATNSimulator.toInt(data[p++]);
@@ -349,7 +368,7 @@ public class ATNSerializer {
 
 	/** Used by Java target to encode short/int array as chars in string. */
 	public static String getSerializedAsString(Grammar g, ATN atn) {
-		return new String(Utils.toCharArray(getSerialized(g, atn)));
+		return new String(getSerializedAsChars(g, atn));
 	}
 
 	public static IntegerList getSerialized(Grammar g, ATN atn) {
@@ -357,7 +376,7 @@ public class ATNSerializer {
 	}
 
 	public static char[] getSerializedAsChars(Grammar g, ATN atn) {
-		return Utils.toCharArray(new ATNSerializer(g, atn).serialize());
+		return Utils.toCharArray(getSerialized(g, atn));
 	}
 
 	public static String getDecoded(Grammar g, ATN atn) {