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 IntIdentityHashBiMiap#nextId()

Optimizes CrudeIncrementalIntIdentityHashBiMap#nextId()

This is a frequent hotspot for world loading/saving.

1.18 note: seems like the bitset is too small now? removing this patch fixed
lots of issues related to synchedentitydata and structure gen. when asked, Tux said "nuke it"

diff --git a/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java b/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
index dc7528b41aa9a55807a2b3e33d5668e1be681e79..a002218caed08bf4a4072d934e1094c22ee35534 100644
--- a/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
+++ b/src/main/java/net/minecraft/util/CrudeIncrementalIntIdentityHashBiMap.java
@@ -16,11 +16,13 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
     private K[] byId;
     private int nextId;
     private int size;
+    private java.util.BitSet usedIds; // Paper
 
     private CrudeIncrementalIntIdentityHashBiMap(int size) {
         this.keys = (K[])(new Object[size]);
         this.values = new int[size];
         this.byId = (K[])(new Object[size]);
+        this.usedIds = new java.util.BitSet(); // Paper
     }
 
     public static <A> CrudeIncrementalIntIdentityHashBiMap<A> create(int expectedSize) {
@@ -57,9 +59,13 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
     }
 
     private int nextId() {
+        /* // Paper start
         while(this.nextId < this.byId.length && this.byId[this.nextId] != null) {
             ++this.nextId;
         }
+        */
+        this.nextId = this.usedIds.nextClearBit(0);
+        // Paper end
 
         return this.nextId;
     }
@@ -80,6 +86,7 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
         this.byId = crudeIncrementalIntIdentityHashBiMap.byId;
         this.nextId = crudeIncrementalIntIdentityHashBiMap.nextId;
         this.size = crudeIncrementalIntIdentityHashBiMap.size;
+        this.usedIds.clear(); // Paper
     }
 
     public void addMapping(K value, int id) {
@@ -96,6 +103,7 @@ 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 +165,7 @@ public class CrudeIncrementalIntIdentityHashBiMap<K> implements IdMap<K> {
         Arrays.fill(this.byId, (Object)null);
         this.nextId = 0;
         this.size = 0;
+        this.usedIds.clear(); // Paper
     }
 
     @Override