From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Andrew Steinborn <git@steinborn.me>
Date: Mon, 23 Jul 2018 13:08:19 -0400
Subject: [PATCH] Optimize RegistryID.c()

This is a frequent hotspot for world loading/saving.

diff --git a/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java b/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
index 66ad412e4368a8615cc66a97ac442c572813a3dd..fa4a2d29b3b4c20d7396e973801d69c4acadddda 100644
--- a/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
+++ b/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
@@ -15,12 +15,14 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
     private K[] byId;
     private int nextId;
     private int size;
+    private java.util.BitSet usedIds; // Paper
 
     public CrudeIncrementalIntIdentityHashBiMap(int size) {
         size = (int) ((float) size / 0.8F);
         this.keys = (K[]) (new Object[size]); // Paper - decompile fix
         this.values = new int[size];
         this.byId = (K[]) (new Object[size]); // Paper - decompile fix
+        this.usedIds = new java.util.BitSet(); // Paper
     }
 
     // Paper start - decompile fix
@@ -52,9 +54,14 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
     }
 
     private int nextId() {
-        while (this.nextId < this.byId.length && this.byId[this.nextId] != null) {
-            ++this.nextId;
+        // Paper start
+        /*
+        while (this.e < this.d.length && this.d[this.e] != null) {
+            ++this.e;
         }
+        */
+        this.nextId = this.usedIds.nextClearBit(0);
+        // Paper end
 
         return this.nextId;
     }
@@ -68,6 +75,7 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
         this.byId = (K[]) (new Object[newSize]); // Paper - decompile fix
         this.nextId = 0;
         this.size = 0;
+        this.usedIds.clear(); // Paper
 
         for (int j = 0; j < ak.length; ++j) {
             if (ak[j] != null) {
@@ -93,6 +101,7 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
         this.keys[k] = value;
         this.values[k] = id;
         this.byId[id] = value;
+        this.usedIds.set(id); // Paper
         ++this.size;
         if (id == this.nextId) {
             ++this.nextId;
@@ -157,6 +166,7 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
         Arrays.fill(this.byId, (Object) null);
         this.nextId = 0;
         this.size = 0;
+        this.usedIds.clear(); // Paper
     }
 
     public int size() {