use fastutil's Object2IntOpenHashMap

proxy/build.gradle

@@ -37,10 +37,53 @@ dependencies {
     runtime 'net.java.dev.jna:jna:4.5.2' // Needed for JLine
     runtime 'com.lmax:disruptor:3.4.2' // Async loggers
 
+    compile 'it.unimi.dsi:fastutil:8.2.1'
+
     testCompile "org.junit.jupiter:junit-jupiter-api:${junitVersion}"
     testCompile "org.junit.jupiter:junit-jupiter-engine:${junitVersion}"
 }
 
+shadowJar {
+    exclude 'it/unimi/dsi/fastutil/booleans/**'
+    exclude 'it/unimi/dsi/fastutil/bytes/**'
+    exclude 'it/unimi/dsi/fastutil/chars/**'
+    exclude 'it/unimi/dsi/fastutil/doubles/**'
+    exclude 'it/unimi/dsi/fastutil/floats/**'
+    exclude 'it/unimi/dsi/fastutil/ints/*Int2*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntAVL*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntArray*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntBi*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntList*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntOpen*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntRB*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntSet*'
+    exclude 'it/unimi/dsi/fastutil/ints/IntSorted*'
+    exclude 'it/unimi/dsi/fastutil/io/**'
+    exclude 'it/unimi/dsi/fastutil/longs/**'
+    exclude 'it/unimi/dsi/fastutil/objects/*ObjectArray*'
+    exclude 'it/unimi/dsi/fastutil/objects/*ObjectAVL*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object*Big*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Boolean*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Byte*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Char*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Double*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Float*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2IntArray*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2IntAVL*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2IntLinked*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object*OpenCustom*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2IntRB*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2IntSorted*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Long*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Object*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Reference*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Object2Short*'
+    exclude 'it/unimi/dsi/fastutil/objects/*ObjectRB*'
+    exclude 'it/unimi/dsi/fastutil/objects/*ObjectSorted*'
+    exclude 'it/unimi/dsi/fastutil/objects/*Reference*'
+    exclude 'it/unimi/dsi/fastutil/shorts/**'
+}
+
 artifacts {
     archives shadowJar
 }

proxy/src/main/java/com/velocitypowered/proxy/protocol/StateRegistry.java

@@ -4,6 +4,8 @@ import com.google.common.primitives.ImmutableIntArray;
 import com.velocitypowered.proxy.protocol.packet.*;
 import io.netty.util.collection.IntObjectHashMap;
 import io.netty.util.collection.IntObjectMap;
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import it.unimi.dsi.fastutil.objects.Object2IntOpenHashMap;
 
 import java.util.*;
 import java.util.function.Supplier;
@@ -217,10 +219,11 @@ public enum StateRegistry {
         public class ProtocolVersion {
             public final int id;
             final IntObjectMap<Supplier<? extends MinecraftPacket>> packetIdToSupplier = new IntObjectHashMap<>(16, 0.5f);
-            final Map<Class<? extends MinecraftPacket>, Integer> packetClassToId = new HashMap<>(16, 0.5f);
+            final Object2IntMap<Class<? extends MinecraftPacket>> packetClassToId = new Object2IntOpenHashMap<>(16, 0.5f);
 
             ProtocolVersion(final int id) {
                 this.id = id;
+                this.packetClassToId.defaultReturnValue(Integer.MIN_VALUE);
             }
 
             public MinecraftPacket createPacket(final int id) {
@@ -232,8 +235,8 @@ public enum StateRegistry {
             }
 
             public int getPacketId(final MinecraftPacket packet) {
-                final Integer id = this.packetClassToId.get(packet.getClass());
-                if (id == null) {
+                final int id = this.packetClassToId.getInt(packet.getClass());
+                if (id == Integer.MIN_VALUE) {
                     throw new IllegalArgumentException(String.format(
                             "Unable to find id for packet of type %s in %s protocol %s",
                             packet.getClass().getName(), PacketRegistry.this.direction, this.id