From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Sun, 20 Jun 2021 16:19:26 -0700
Subject: [PATCH] Optimise random block ticking

Massive performance improvement for random block ticking.
The performance increase comes from the fact that the vast
majority of attempted block ticks (~95% in my testing) fail
because the randomly selected block is not tickable.

Now only tickable blocks are targeted, however this means that
the maximum number of block ticks occurs per chunk. However,
not all chunks are going to be targeted. The percent chance
of a chunk being targeted is based on how many tickable blocks
are in the chunk.
This means that while block ticks are spread out less, the
total number of blocks ticked per world tick remains the same.
Therefore, the chance of a random tickable block being ticked
remains the same.

diff --git a/src/main/java/io/papermc/paper/util/math/ThreadUnsafeRandom.java b/src/main/java/io/papermc/paper/util/math/ThreadUnsafeRandom.java
new file mode 100644
index 0000000000000000000000000000000000000000..7d93652c1abbb6aee6eb7c26cf35d4d032ef7b69
--- /dev/null
+++ b/src/main/java/io/papermc/paper/util/math/ThreadUnsafeRandom.java
@@ -0,0 +1,65 @@
+package io.papermc.paper.util.math;
+
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.levelgen.LegacyRandomSource;
+import net.minecraft.world.level.levelgen.PositionalRandomFactory;
+import org.checkerframework.checker.nullness.qual.NonNull;
+import org.checkerframework.framework.qual.DefaultQualifier;
+
+@DefaultQualifier(NonNull.class)
+public final class ThreadUnsafeRandom extends LegacyRandomSource {
+
+    // See javadoc and internal comments for java.util.Random where these values come from, how they are used, and the author for them.
+    private static final long multiplier = 0x5DEECE66DL;
+    private static final long addend = 0xBL;
+    private static final long mask = (1L << 48) - 1;
+
+    private static long initialScramble(long seed) {
+        return (seed ^ multiplier) & mask;
+    }
+
+    private long seed;
+
+    public ThreadUnsafeRandom(long seed) {
+        super(seed);
+    }
+
+    @Override
+    public RandomSource fork() {
+        return new ThreadUnsafeRandom(this.nextLong());
+    }
+
+    @Override
+    public PositionalRandomFactory forkPositional() {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void setSeed(long seed) {
+        // note: called by Random constructor
+        this.seed = initialScramble(seed);
+    }
+
+    @Override
+    public int next(int bits) {
+        // avoid the expensive CAS logic used by superclass
+        return (int) (((this.seed = this.seed * multiplier + addend) & mask) >>> (48 - bits));
+    }
+
+    // Taken from
+    // https://lemire.me/blog/2016/06/27/a-fast-alternative-to-the-modulo-reduction/
+    // https://github.com/lemire/Code-used-on-Daniel-Lemire-s-blog/blob/master/2016/06/25/fastrange.c
+    // Original license is public domain
+    public static int fastRandomBounded(final long randomInteger, final long limit) {
+        // randomInteger must be [0, pow(2, 32))
+        // limit must be [0, pow(2, 32))
+        return (int)((randomInteger * limit) >>> 32);
+    }
+
+    @Override
+    public int nextInt(int bound) {
+        // yes this breaks random's spec
+        // however there's nothing that uses this class that relies on it
+        return fastRandomBounded(this.next(32) & 0xFFFFFFFFL, bound);
+    }
+}
diff --git a/src/main/java/net/minecraft/server/level/ServerLevel.java b/src/main/java/net/minecraft/server/level/ServerLevel.java
index 3a49f8933bc6ca1862994b7e0b3006f5236dd94a..bdad61438e7fd89f5f0cac6632dd395fcf024361 100644
--- a/src/main/java/net/minecraft/server/level/ServerLevel.java
+++ b/src/main/java/net/minecraft/server/level/ServerLevel.java
@@ -861,6 +861,10 @@ public class ServerLevel extends Level implements WorldGenLevel {
             entityplayer.stopSleepInBed(false, false);
         });
     }
+    // Paper start - optimise random block ticking
+    private final BlockPos.MutableBlockPos chunkTickMutablePosition = new BlockPos.MutableBlockPos();
+    private final io.papermc.paper.util.math.ThreadUnsafeRandom randomTickRandom = new io.papermc.paper.util.math.ThreadUnsafeRandom(this.random.nextLong());
+    // Paper end
 
     public void tickChunk(LevelChunk chunk, int randomTickSpeed) {
         ChunkPos chunkcoordintpair = chunk.getPos();
@@ -870,8 +874,10 @@ public class ServerLevel extends Level implements WorldGenLevel {
         ProfilerFiller gameprofilerfiller = this.getProfiler();
 
         gameprofilerfiller.push("thunder");
+        final BlockPos.MutableBlockPos blockposition = this.chunkTickMutablePosition; // Paper - use mutable to reduce allocation rate, final to force compile fail on change
+
         if (!this.paperConfig().environment.disableThunder && flag && this.isThundering() && this.spigotConfig.thunderChance > 0 && this.random.nextInt(this.spigotConfig.thunderChance) == 0) { // Spigot // Paper - Option to disable thunder
-            BlockPos blockposition = this.findLightningTargetAround(this.getBlockRandomPos(j, 0, k, 15));
+            blockposition.set(this.findLightningTargetAround(this.getBlockRandomPos(j, 0, k, 15))); // Paper
 
             if (this.isRainingAt(blockposition)) {
                 DifficultyInstance difficultydamagescaler = this.getCurrentDifficultyAt(blockposition);
@@ -903,7 +909,10 @@ public class ServerLevel extends Level implements WorldGenLevel {
         if (!this.paperConfig().environment.disableIceAndSnow) { // Paper - Option to disable ice and snow
         for (int l = 0; l < randomTickSpeed; ++l) {
             if (this.random.nextInt(48) == 0) {
-                this.tickPrecipitation(this.getBlockRandomPos(j, 0, k, 15));
+                // Paper start
+                this.getRandomBlockPosition(j, 0, k, 15, blockposition);
+                this.tickPrecipitation(blockposition, chunk);
+                // Paper end
             }
         }
         } // Paper - Option to disable ice and snow
@@ -911,36 +920,37 @@ public class ServerLevel extends Level implements WorldGenLevel {
         gameprofilerfiller.popPush("tickBlocks");
         timings.chunkTicksBlocks.startTiming(); // Paper
         if (randomTickSpeed > 0) {
-            LevelChunkSection[] achunksection = chunk.getSections();
-
-            for (int i1 = 0; i1 < achunksection.length; ++i1) {
-                LevelChunkSection chunksection = achunksection[i1];
-
-                if (chunksection.isRandomlyTicking()) {
-                    int j1 = chunk.getSectionYFromSectionIndex(i1);
-                    int k1 = SectionPos.sectionToBlockCoord(j1);
-
-                    for (int l1 = 0; l1 < randomTickSpeed; ++l1) {
-                        BlockPos blockposition1 = this.getBlockRandomPos(j, k1, k, 15);
-
-                        gameprofilerfiller.push("randomTick");
-                        BlockState iblockdata = chunksection.getBlockState(blockposition1.getX() - j, blockposition1.getY() - k1, blockposition1.getZ() - k);
-
-                        if (iblockdata.isRandomlyTicking()) {
-                            iblockdata.randomTick(this, blockposition1, this.random);
-                        }
+            // Paper start - optimize random block ticking
+            LevelChunkSection[] sections = chunk.getSections();
+            final int minSection = io.papermc.paper.util.WorldUtil.getMinSection(this);
+            for (int sectionIndex = 0; sectionIndex < sections.length; sectionIndex++) {
+                LevelChunkSection section = sections[sectionIndex];
+                if (section == null || section.tickingList.size() == 0) continue;
+
+                int yPos = (sectionIndex + minSection) << 4;
+                for (int a = 0; a < randomTickSpeed; ++a) {
+                    int tickingBlocks = section.tickingList.size();
+                    int index = this.randomTickRandom.nextInt(16 * 16 * 16);
+                    if (index >= tickingBlocks) {
+                        continue;
+                    }
 
-                        FluidState fluid = iblockdata.getFluidState();
+                    long raw = section.tickingList.getRaw(index);
+                    int location = com.destroystokyo.paper.util.maplist.IBlockDataList.getLocationFromRaw(raw);
+                    int randomX = location & 15;
+                    int randomY = ((location >>> (4 + 4)) & 255) | yPos;
+                    int randomZ = (location >>> 4) & 15;
 
-                        if (fluid.isRandomlyTicking()) {
-                            fluid.randomTick(this, blockposition1, this.random);
-                        }
+                    BlockPos blockposition2 = blockposition.set(j + randomX, randomY, k + randomZ);
+                    BlockState iblockdata = com.destroystokyo.paper.util.maplist.IBlockDataList.getBlockDataFromRaw(raw);
 
-                        gameprofilerfiller.pop();
-                    }
+                    iblockdata.randomTick(this, blockposition2, this.randomTickRandom);
                 }
+                // We drop the fluid tick since LAVA is ALREADY TICKED by the above method (See LiquidBlock).
+                // TODO CHECK ON UPDATE (ping the Canadian)
             }
         }
+        // Paper end - optimise random block ticking
 
         timings.chunkTicksBlocks.stopTiming(); // Paper
         gameprofilerfiller.pop();
@@ -948,17 +958,25 @@ public class ServerLevel extends Level implements WorldGenLevel {
 
     @VisibleForTesting
     public void tickPrecipitation(BlockPos pos) {
-        BlockPos blockposition1 = this.getHeightmapPos(Heightmap.Types.MOTION_BLOCKING, pos);
-        BlockPos blockposition2 = blockposition1.below();
+    // Paper start - optimise chunk ticking
+        tickPrecipitation(pos.mutable(), this.getChunkAt(pos));
+    }
+    public void tickPrecipitation(BlockPos.MutableBlockPos blockposition1, final LevelChunk chunk) {
+        int normalY = chunk.getHeight(Heightmap.Types.MOTION_BLOCKING, blockposition1.getX() & 15, blockposition1.getZ() & 15) + 1;
+        int downY = normalY - 1;
+        blockposition1.setY(normalY);
+        // Paper end - optimise chunk ticking
         Biome biomebase = (Biome) this.getBiome(blockposition1).value();
 
-        if (biomebase.shouldFreeze(this, blockposition2)) {
-            org.bukkit.craftbukkit.event.CraftEventFactory.handleBlockFormEvent(this, blockposition2, Blocks.ICE.defaultBlockState(), null); // CraftBukkit
+        blockposition1.setY(downY);
+        if (biomebase.shouldFreeze(this, blockposition1)) {
+            org.bukkit.craftbukkit.event.CraftEventFactory.handleBlockFormEvent(this, blockposition1, Blocks.ICE.defaultBlockState(), null); // CraftBukkit
         }
 
         if (this.isRaining()) {
             int i = this.getGameRules().getInt(GameRules.RULE_SNOW_ACCUMULATION_HEIGHT);
 
+            blockposition1.setY(normalY); // Paper - optimise chunk ticking
             if (i > 0 && biomebase.shouldSnow(this, blockposition1)) {
                 BlockState iblockdata = this.getBlockState(blockposition1);
 
@@ -976,12 +994,13 @@ public class ServerLevel extends Level implements WorldGenLevel {
                 }
             }
 
-            Biome.Precipitation biomebase_precipitation = biomebase.getPrecipitationAt(blockposition2);
+            blockposition1.setY(downY); // Paper - optimise chunk ticking
+            Biome.Precipitation biomebase_precipitation = biomebase.getPrecipitationAt(blockposition1); // Paper - optimise chunk ticking
 
             if (biomebase_precipitation != Biome.Precipitation.NONE) {
-                BlockState iblockdata2 = this.getBlockState(blockposition2);
+                BlockState iblockdata2 = this.getBlockState(blockposition1); // Paper - optimise chunk ticking
 
-                iblockdata2.getBlock().handlePrecipitation(iblockdata2, this, blockposition2, biomebase_precipitation);
+                iblockdata2.getBlock().handlePrecipitation(iblockdata2, this, blockposition1, biomebase_precipitation); // Paper - optimise chunk ticking
             }
         }
 
diff --git a/src/main/java/net/minecraft/util/BitStorage.java b/src/main/java/net/minecraft/util/BitStorage.java
index 68648c5a5e3ff079f832092af0f2f801c42d1ede..8bafd5fd7499ba4a04bf706cfd1e156073716e21 100644
--- a/src/main/java/net/minecraft/util/BitStorage.java
+++ b/src/main/java/net/minecraft/util/BitStorage.java
@@ -20,4 +20,15 @@ public interface BitStorage {
     void unpack(int[] out);
 
     BitStorage copy();
+
+    // Paper start
+    void forEach(DataBitConsumer consumer);
+
+    @FunctionalInterface
+    interface DataBitConsumer {
+
+        void accept(int location, int data);
+
+    }
+    // Paper end
 }
diff --git a/src/main/java/net/minecraft/util/SimpleBitStorage.java b/src/main/java/net/minecraft/util/SimpleBitStorage.java
index 9f438d9c6eb05e43d24e4af68188a3d4c46a938c..8d7d763bf51cac556057645e6169c9447993189b 100644
--- a/src/main/java/net/minecraft/util/SimpleBitStorage.java
+++ b/src/main/java/net/minecraft/util/SimpleBitStorage.java
@@ -315,6 +315,28 @@ public class SimpleBitStorage implements BitStorage {
         return this.bits;
     }
 
+    // Paper start
+    @Override
+    public final void forEach(DataBitConsumer consumer) {
+        int i = 0;
+        long[] along = this.data;
+        int j = along.length;
+
+        for (int k = 0; k < j; ++k) {
+            long l = along[k];
+
+            for (int i1 = 0; i1 < this.valuesPerLong; ++i1) {
+                consumer.accept(i, (int) (l & this.mask));
+                l >>= this.bits;
+                ++i;
+                if (i >= this.size) {
+                    return;
+                }
+            }
+        }
+    }
+    // Paper end
+
     @Override
     public void getAll(IntConsumer action) {
         int i = 0;
diff --git a/src/main/java/net/minecraft/util/ZeroBitStorage.java b/src/main/java/net/minecraft/util/ZeroBitStorage.java
index 50040c497a819cd1229042ab3cb057d34a32cacc..01f5b946fabbe34f31110e75973dab9f39897346 100644
--- a/src/main/java/net/minecraft/util/ZeroBitStorage.java
+++ b/src/main/java/net/minecraft/util/ZeroBitStorage.java
@@ -46,6 +46,15 @@ public class ZeroBitStorage implements BitStorage {
         return 0;
     }
 
+    // Paper start
+    @Override
+    public void forEach(DataBitConsumer consumer) {
+        for(int i = 0; i < this.size; ++i) {
+            consumer.accept(i, 0);
+        }
+    }
+    // Paper end
+
     @Override
     public void getAll(IntConsumer action) {
         for (int i = 0; i < this.size; i++) {
diff --git a/src/main/java/net/minecraft/world/entity/animal/Turtle.java b/src/main/java/net/minecraft/world/entity/animal/Turtle.java
index ffffa53fcaa6ec8681b283fa20bb5a3320ad9c11..30b87b5cb18c25cdd04eab64cfbe5acd6c1b6d84 100644
--- a/src/main/java/net/minecraft/world/entity/animal/Turtle.java
+++ b/src/main/java/net/minecraft/world/entity/animal/Turtle.java
@@ -88,7 +88,7 @@ public class Turtle extends Animal {
     }
 
     public void setHomePos(BlockPos pos) {
-        this.entityData.set(Turtle.HOME_POS, pos);
+        this.entityData.set(Turtle.HOME_POS, pos.immutable()); // Paper - called with mutablepos...
     }
 
     public BlockPos getHomePos() {
diff --git a/src/main/java/net/minecraft/world/level/Level.java b/src/main/java/net/minecraft/world/level/Level.java
index dab55ab08665f2b5ae0c899a4ab07c18460552ae..4001bec504b8fcda1eec03f49abd4e4d82cf6336 100644
--- a/src/main/java/net/minecraft/world/level/Level.java
+++ b/src/main/java/net/minecraft/world/level/Level.java
@@ -1387,10 +1387,18 @@ public abstract class Level implements LevelAccessor, AutoCloseable {
     public abstract RecipeManager getRecipeManager();
 
     public BlockPos getBlockRandomPos(int x, int y, int z, int l) {
+        // Paper start - allow use of mutable pos
+        BlockPos.MutableBlockPos ret = new BlockPos.MutableBlockPos();
+        this.getRandomBlockPosition(x, y, z, l, ret);
+        return ret.immutable();
+    }
+    public final BlockPos.MutableBlockPos getRandomBlockPosition(int x, int y, int z, int l, BlockPos.MutableBlockPos out) {
+        // Paper end
         this.randValue = this.randValue * 3 + 1013904223;
         int i1 = this.randValue >> 2;
 
-        return new BlockPos(x + (i1 & 15), y + (i1 >> 16 & l), z + (i1 >> 8 & 15));
+        out.set(x + (i1 & 15), y + (i1 >> 16 & l), z + (i1 >> 8 & 15)); // Paper - change to setValues call
+        return out; // Paper
     }
 
     public boolean noSave() {
diff --git a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
index f2e11bff414b521295bde721e01ae2166a6a3fd6..8cd6c1d838e0332125fde3fc36475034aa4effa0 100644
--- a/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
+++ b/src/main/java/net/minecraft/world/level/chunk/LevelChunkSection.java
@@ -25,6 +25,7 @@ public class LevelChunkSection {
     public final PalettedContainer<BlockState> states;
     // CraftBukkit start - read/write
     private PalettedContainer<Holder<Biome>> biomes;
+    public final com.destroystokyo.paper.util.maplist.IBlockDataList tickingList = new com.destroystokyo.paper.util.maplist.IBlockDataList(); // Paper
 
     public LevelChunkSection(PalettedContainer<BlockState> datapaletteblock, PalettedContainer<Holder<Biome>> palettedcontainerro) {
         // CraftBukkit end
@@ -77,6 +78,9 @@ public class LevelChunkSection {
             --this.nonEmptyBlockCount;
             if (iblockdata1.isRandomlyTicking()) {
                 --this.tickingBlockCount;
+                // Paper start
+                this.tickingList.remove(x, y, z);
+                // Paper end
             }
         }
 
@@ -88,6 +92,9 @@ public class LevelChunkSection {
             ++this.nonEmptyBlockCount;
             if (state.isRandomlyTicking()) {
                 ++this.tickingBlockCount;
+                // Paper start
+                this.tickingList.add(x, y, z, state);
+                // Paper end
             }
         }
 
@@ -115,40 +122,34 @@ public class LevelChunkSection {
     }
 
     public void recalcBlockCounts() {
-        class a implements PalettedContainer.CountConsumer<BlockState> {
-
-            public int nonEmptyBlockCount;
-            public int tickingBlockCount;
-            public int tickingFluidCount;
-
-            a(final LevelChunkSection chunksection) {}
-
-            public void accept(BlockState iblockdata, int i) {
+        // Paper start - unfuck this
+        this.tickingList.clear();
+        this.nonEmptyBlockCount = 0;
+        this.tickingBlockCount = 0;
+        this.tickingFluidCount = 0;
+        // Don't run this on clearly empty sections
+        if (this.maybeHas((BlockState state) -> !state.isAir() || !state.getFluidState().isEmpty())) {
+            this.states.forEachLocation((BlockState iblockdata, int i) -> {
                 FluidState fluid = iblockdata.getFluidState();
 
                 if (!iblockdata.isAir()) {
-                    this.nonEmptyBlockCount += i;
+                    this.nonEmptyBlockCount = (short) (this.nonEmptyBlockCount + 1);
                     if (iblockdata.isRandomlyTicking()) {
-                        this.tickingBlockCount += i;
+                        this.tickingBlockCount = (short)(this.tickingBlockCount + 1);
+                        this.tickingList.add(i, iblockdata);
                     }
                 }
 
                 if (!fluid.isEmpty()) {
-                    this.nonEmptyBlockCount += i;
+                    this.nonEmptyBlockCount = (short) (this.nonEmptyBlockCount + 1);
                     if (fluid.isRandomlyTicking()) {
-                        this.tickingFluidCount += i;
+                        this.tickingFluidCount = (short) (this.tickingFluidCount + 1);
                     }
                 }
 
-            }
+            });
         }
-
-        a a0 = new a(this);
-
-        this.states.count(a0);
-        this.nonEmptyBlockCount = (short) a0.nonEmptyBlockCount;
-        this.tickingBlockCount = (short) a0.tickingBlockCount;
-        this.tickingFluidCount = (short) a0.tickingFluidCount;
+        // Paper end - unfuck this
     }
 
     public PalettedContainer<BlockState> getStates() {
diff --git a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
index 926c81a25180d508d662eb3fa35f771636164694..81368bf186365878db2e1ed305bb7bf36c26f61f 100644
--- a/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
+++ b/src/main/java/net/minecraft/world/level/chunk/PalettedContainer.java
@@ -381,6 +381,14 @@ public class PalettedContainer<T> implements PaletteResize<T>, PalettedContainer
         }
     }
 
+    // Paper start
+    public void forEachLocation(PalettedContainer.CountConsumer<T> consumer) {
+        this.data.storage.forEach((int location, int data) -> {
+            consumer.accept(this.data.palette.valueFor(data), location);
+        });
+    }
+    // Paper end
+
     @FunctionalInterface
     public interface CountConsumer<T> {
         void accept(T object, int count);
