SparklyPaperMC/patches/server/0019-Use-aging-cache-for-biome-temperatures.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Paul Sauve <paul@technove.co>
Date: Tue, 22 Jun 2021 14:49:50 -0500
Subject: [PATCH] Use aging cache for biome temperatures


diff --git a/src/main/java/gg/airplane/structs/Long2FloatAgingCache.java b/src/main/java/gg/airplane/structs/Long2FloatAgingCache.java
new file mode 100644
index 0000000000000000000000000000000000000000..a7f297ebb569f7c1f205e967ca485be70013a714
--- /dev/null
+++ b/src/main/java/gg/airplane/structs/Long2FloatAgingCache.java
@@ -0,0 +1,119 @@
+package gg.airplane.structs;
+
+import it.unimi.dsi.fastutil.HashCommon;
+
+/**
+ * A replacement for the cache used in Biome.
+ */
+public class Long2FloatAgingCache {
+
+    private static class AgingEntry {
+        private long data;
+        private float value;
+        private int uses = 0;
+        private int age = 0;
+
+        private AgingEntry(long data, float value) {
+            this.data = data;
+            this.value = value;
+        }
+
+        public void replace(long data, float flag) {
+            this.data = data;
+            this.value = flag;
+        }
+
+        public int getValue() {
+            return this.uses - (this.age >> 1); // age isn't as important as uses
+        }
+
+        public void incrementUses() {
+            this.uses = this.uses + 1 & Integer.MAX_VALUE;
+        }
+
+        public void incrementAge() {
+            this.age = this.age + 1 & Integer.MAX_VALUE;
+        }
+    }
+
+    private final AgingEntry[] entries;
+    private final int mask;
+    private final int maxDistance; // the most amount of entries to check for a value
+
+    public Long2FloatAgingCache(int size) {
+        int arraySize = HashCommon.nextPowerOfTwo(size);
+        this.entries = new AgingEntry[arraySize];
+        this.mask = arraySize - 1;
+        this.maxDistance = Math.min(arraySize, 4);
+    }
+
+    public float getValue(long data) {
+        AgingEntry curr;
+        int pos;
+
+        if ((curr = this.entries[pos = HashCommon.mix(HashCommon.long2int(data)) & this.mask]) == null) {
+            return Float.NaN;
+        } else if (data == curr.data) {
+            curr.incrementUses();
+            return curr.value;
+        }
+
+        int checked = 1; // start at 1 because we already checked the first spot above
+
+        while ((curr = this.entries[pos = (pos + 1) & this.mask]) != null) {
+            if (data == curr.data) {
+                curr.incrementUses();
+                return curr.value;
+            } else if (++checked >= this.maxDistance) {
+                break;
+            }
+        }
+
+        return Float.NaN;
+    }
+
+    public void putValue(long data, float value) {
+        AgingEntry curr;
+        int pos;
+
+        if ((curr = this.entries[pos = HashCommon.mix(HashCommon.long2int(data)) & this.mask]) == null) {
+            this.entries[pos] = new AgingEntry(data, value); // add
+            return;
+        } else if (data == curr.data) {
+            curr.incrementUses();
+            return;
+        }
+
+        int checked = 1; // start at 1 because we already checked the first spot above
+
+        while ((curr = this.entries[pos = (pos + 1) & this.mask]) != null) {
+            if (data == curr.data) {
+                curr.incrementUses();
+                return;
+            } else if (++checked >= this.maxDistance) {
+                this.forceAdd(data, value);
+                return;
+            }
+        }
+
+        this.entries[pos] = new AgingEntry(data, value); // add
+    }
+
+    private void forceAdd(long data, float value) {
+        int expectedPos = HashCommon.mix(HashCommon.long2int(data)) & this.mask;
+        AgingEntry entryToRemove = this.entries[expectedPos];
+
+        for (int i = expectedPos + 1; i < expectedPos + this.maxDistance; i++) {
+            int pos = i & this.mask;
+            AgingEntry entry = this.entries[pos];
+            if (entry.getValue() < entryToRemove.getValue()) {
+                entryToRemove = entry;
+            }
+
+            entry.incrementAge(); // use this as a mechanism to age the other entries
+        }
+
+        // remove the least used/oldest entry
+        entryToRemove.replace(data, value);
+    }
+}
diff --git a/src/main/java/net/minecraft/world/level/biome/Biome.java b/src/main/java/net/minecraft/world/level/biome/Biome.java
index a7a7e6cd87270e64a92448f03f8b0b0c7e375ec7..0ea6fedf6e660bc133fd5eb34d3d9bac3e581f32 100644
--- a/src/main/java/net/minecraft/world/level/biome/Biome.java
+++ b/src/main/java/net/minecraft/world/level/biome/Biome.java
@@ -104,8 +104,10 @@ public final class Biome {
     private final float scale;
     private final Biome.BiomeCategory biomeCategory;
     private final BiomeSpecialEffects specialEffects;
-    private final ThreadLocal<Long2FloatLinkedOpenHashMap> temperatureCache = ThreadLocal.withInitial(() -> {
+    // Airplane start - use our cache
+    private final ThreadLocal<gg.airplane.structs.Long2FloatAgingCache> temperatureCache = ThreadLocal.withInitial(() -> {
         return Util.make(() -> {
+            /*
             Long2FloatLinkedOpenHashMap long2FloatLinkedOpenHashMap = new Long2FloatLinkedOpenHashMap(1024, 0.25F) {
                 @Override
                 protected void rehash(int i) {
@@ -113,6 +115,10 @@ public final class Biome {
             };
             long2FloatLinkedOpenHashMap.defaultReturnValue(Float.NaN);
             return long2FloatLinkedOpenHashMap;
+
+             */
+            return new gg.airplane.structs.Long2FloatAgingCache(TEMPERATURE_CACHE_SIZE);
+            // Airplane end
         });
     });
 
@@ -154,17 +160,15 @@ public final class Biome {
 
     public final float getTemperature(BlockPos blockPos) {
         long l = blockPos.asLong();
-        Long2FloatLinkedOpenHashMap long2FloatLinkedOpenHashMap = this.temperatureCache.get();
-        float f = long2FloatLinkedOpenHashMap.get(l);
+        // Airplane start
+        gg.airplane.structs.Long2FloatAgingCache cache = this.temperatureCache.get();
+        float f = cache.getValue(l);
         if (!Float.isNaN(f)) {
             return f;
         } else {
             float g = this.getHeightAdjustedTemperature(blockPos);
-            if (long2FloatLinkedOpenHashMap.size() == 1024) {
-                long2FloatLinkedOpenHashMap.removeFirstFloat();
-            }
-
-            long2FloatLinkedOpenHashMap.put(l, g);
+            cache.putValue(l, g);
+            // Airplane end
             return g;
         }
     }