From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: SuperCoder7979 <25208576+SuperCoder7979@users.noreply.github.com>
Date: Tue, 3 Nov 2020 23:48:05 -0600
Subject: [PATCH] Significantly improve performance of the end generation

This patch implements a noise cache for the end which significantly reduces the computation time of generation. This results in about a 3x improvement.

Original code by SuperCoder7979 and Gegy in Lithium, licensed under LGPL-3.0 (Source: https://github.com/jellysquid3/lithium-fabric)

Co-authored-by: Gegy <gegy1000@gmail.com>
Co-authored-by: Dylan Xaldin <Puremin0rez515@gmail.com>
Co-authored-by: pop4959 <pop4959@gmail.com>

diff --git a/src/main/java/net/minecraft/server/WorldChunkManagerTheEnd.java b/src/main/java/net/minecraft/server/WorldChunkManagerTheEnd.java
index 9c15cd303ccc2928be4e3e7080e74e8314d7e0f2..70924c2942f6cc668eb4d11afdb42a966bd5edc8 100644
--- a/src/main/java/net/minecraft/server/WorldChunkManagerTheEnd.java
+++ b/src/main/java/net/minecraft/server/WorldChunkManagerTheEnd.java
@@ -3,6 +3,7 @@ package net.minecraft.server;
 import com.google.common.collect.ImmutableList;
 import com.mojang.serialization.Codec;
 import com.mojang.serialization.codecs.RecordCodecBuilder;
+import it.unimi.dsi.fastutil.HashCommon; // Paper
 import java.util.List;
 
 public class WorldChunkManagerTheEnd extends WorldChunkManager {
@@ -22,6 +23,16 @@ public class WorldChunkManagerTheEnd extends WorldChunkManager {
     private final BiomeBase k;
     private final BiomeBase l;
     private final BiomeBase m;
+    // Paper start
+    private static final class NoiseCache {
+        public long[] keys = new long[8192];
+        public float[] values = new float[8192];
+        public NoiseCache() {
+            java.util.Arrays.fill(keys, Long.MIN_VALUE);
+        }
+    }
+    private static final ThreadLocal<java.util.Map<NoiseGenerator3Handler, NoiseCache>> noiseCache = ThreadLocal.withInitial(java.util.WeakHashMap::new);
+    // Paper end
 
     public WorldChunkManagerTheEnd(IRegistry<BiomeBase> iregistry, long i) {
         this(iregistry, i, (BiomeBase) iregistry.d(Biomes.THE_END), (BiomeBase) iregistry.d(Biomes.END_HIGHLANDS), (BiomeBase) iregistry.d(Biomes.END_MIDLANDS), (BiomeBase) iregistry.d(Biomes.SMALL_END_ISLANDS), (BiomeBase) iregistry.d(Biomes.END_BARRENS));
@@ -76,13 +87,27 @@ public class WorldChunkManagerTheEnd extends WorldChunkManager {
 
         f = MathHelper.a(f, -100.0F, 80.0F);
 
+        NoiseCache cache = noiseCache.get().computeIfAbsent(noisegenerator3handler, m -> new NoiseCache()); // Paper
         for (int k1 = -12; k1 <= 12; ++k1) {
             for (int l1 = -12; l1 <= 12; ++l1) {
                 long i2 = (long) (k + k1);
                 long j2 = (long) (l + l1);
 
-                if (i2 * i2 + j2 * j2 > 4096L && noisegenerator3handler.a((double) i2, (double) j2) < -0.8999999761581421D) {
-                    float f1 = (MathHelper.e((float) i2) * 3439.0F + MathHelper.e((float) j2) * 147.0F) % 13.0F + 9.0F;
+                // Paper start - Significantly improve end generation performance by using a noise cache
+                long key = ChunkCoordIntPair.pair((int) i2, (int) j2);
+                int index = (int) HashCommon.mix(key) & 8191;
+                float f1 = Float.MIN_VALUE;
+                if (cache.keys[index] == key) {
+                    f1 = cache.values[index];
+                } else {
+                    if (i2 * i2 + j2 * j2 > 4096L && noisegenerator3handler.a((double) i2, (double) j2) < -0.8999999761581421D) {
+                        f1 = (MathHelper.e((float) i2) * 3439.0F + MathHelper.e((float) j2) * 147.0F) % 13.0F + 9.0F;
+                    }
+                    cache.keys[index] = key;
+                    cache.values[index] = f1;
+                }
+                if (f1 != Float.MIN_VALUE) {
+                    // Paper end
                     float f2 = (float) (i1 - k1 * 2);
                     float f3 = (float) (j1 - l1 * 2);
                     float f4 = 100.0F - MathHelper.c(f2 * f2 + f3 * f3) * f1;