From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: CullanP <cullanpage@gmail.com>
Date: Thu, 3 Mar 2016 02:13:38 -0600
Subject: [PATCH] Avoid hopper searches if there are no items

Hoppers searching for items and minecarts is the most expensive part of hopper ticking.
We keep track of the number of minecarts and items in a chunk.
If there are no items in the chunk, we skip searching for items.
If there are no minecarts in the chunk, we skip searching for them.

Usually hoppers aren't near items, so we can skip most item searches.
And since minecart hoppers are used _very_ rarely near we can avoid alot of searching there.

Combined, this adds up a lot.

diff --git a/src/main/java/net/minecraft/server/Chunk.java b/src/main/java/net/minecraft/server/Chunk.java
index 2604fe9756e90cb70d3d527edddb917772e70973..a2a0ca3394c3231aad9888fecebdaf82d4d9e9f7 100644
--- a/src/main/java/net/minecraft/server/Chunk.java
+++ b/src/main/java/net/minecraft/server/Chunk.java
@@ -84,6 +84,10 @@ public class Chunk implements IChunkAccess {
             return removed;
         }
     }
+    // Track the number of minecarts and items
+    // Keep this synced with entitySlices.add() and entitySlices.remove()
+    private final int[] itemCounts = new int[16];
+    private final int[] inventoryEntityCounts = new int[16];
     // Paper end
 
     public Chunk(World world, ChunkCoordIntPair chunkcoordintpair, BiomeStorage biomestorage, ChunkConverter chunkconverter, TickList<Block> ticklist, TickList<FluidType> ticklist1, long i, @Nullable ChunkSection[] achunksection, @Nullable Consumer<Chunk> consumer) {
@@ -532,6 +536,13 @@ public class Chunk implements IChunkAccess {
         entity.chunkZ = this.loc.z;
         this.entities.add(entity); // Paper - per chunk entity list
         this.entitySlices[k].add(entity);
+        // Paper start
+        if (entity instanceof EntityItem) {
+            itemCounts[k]++;
+        } else if (entity instanceof IInventory) {
+            inventoryEntityCounts[k]++;
+        }
+        // Paper end
         entity.entitySlice = this.entitySlices[k]; // Paper
         this.markDirty(); // Paper
     }
@@ -564,6 +575,11 @@ public class Chunk implements IChunkAccess {
         if (!this.entitySlices[i].remove(entity)) {
             return;
         }
+        if (entity instanceof EntityItem) {
+            itemCounts[i]--;
+        } else if (entity instanceof IInventory) {
+            inventoryEntityCounts[i]--;
+        }
         entityCounts.decrement(entity.getMinecraftKeyString());
         this.markDirty(); // Paper
         // Paper end
@@ -847,6 +863,14 @@ public class Chunk implements IChunkAccess {
         for (int k = i; k <= j; ++k) {
             Iterator iterator = this.entitySlices[k].iterator(); // Spigot
 
+            // Paper start - Don't search for inventories if we have none, and that is all we want
+            /*
+             * We check if they want inventories by seeing if it is the static `IEntitySelector.d`
+             *
+             * Make sure the inventory selector stays in sync.
+             * It should be the one that checks `var1 instanceof IInventory && var1.isAlive()`
+             */
+            if (predicate == IEntitySelector.isInventory() && inventoryEntityCounts[k] <= 0) continue;
             while (iterator.hasNext()) {
                 T entity = (T) iterator.next(); // CraftBukkit - decompile error
                 if (entity.shouldBeRemoved) continue; // Paper
@@ -866,9 +890,29 @@ public class Chunk implements IChunkAccess {
         i = MathHelper.clamp(i, 0, this.entitySlices.length - 1);
         j = MathHelper.clamp(j, 0, this.entitySlices.length - 1);
 
+        // Paper start
+        int[] counts;
+        if (EntityItem.class.isAssignableFrom(oclass)) {
+            counts = itemCounts;
+        } else if (IInventory.class.isAssignableFrom(oclass)) {
+            counts = inventoryEntityCounts;
+        } else {
+            counts = null;
+        }
+        // Paper end
         for (int k = i; k <= j; ++k) {
+            if (counts != null && counts[k] <= 0) continue; // Paper - Don't check a chunk if it doesn't have the type we are looking for
             Iterator iterator = this.entitySlices[k].iterator(); // Spigot
 
+            // Paper start - Don't search for inventories if we have none, and that is all we want
+            /*
+             * We check if they want inventories by seeing if it is the static `IEntitySelector.d`
+             *
+             * Make sure the inventory selector stays in sync.
+             * It should be the one that checks `var1 instanceof IInventory && var1.isAlive()`
+             */
+            if (predicate == IEntitySelector.isInventory() && inventoryEntityCounts[k] <= 0) continue;
+            // Paper end
             while (iterator.hasNext()) {
                 T t0 = (T) iterator.next(); // CraftBukkit - decompile error
                 if (t0.shouldBeRemoved) continue; // Paper
diff --git a/src/main/java/net/minecraft/server/IEntitySelector.java b/src/main/java/net/minecraft/server/IEntitySelector.java
index 498f381099b2cf9460104688e12afc5f586e057a..a2d1ef3602a1c63d106d10140e18dfdb1d490805 100644
--- a/src/main/java/net/minecraft/server/IEntitySelector.java
+++ b/src/main/java/net/minecraft/server/IEntitySelector.java
@@ -11,6 +11,7 @@ public final class IEntitySelector {
     public static final Predicate<Entity> c = (entity) -> {
         return entity.isAlive() && !entity.isVehicle() && !entity.isPassenger();
     };
+    public static final Predicate<Entity> isInventory() { return d; } // Paper - OBFHELPER
     public static final Predicate<Entity> d = (entity) -> {
         return entity instanceof IInventory && entity.isAlive();
     };
