Paper/patches/server/0401-Optimise-ArraySetSorted-removeIf.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Spottedleaf <Spottedleaf@users.noreply.github.com>
Date: Wed, 15 Apr 2020 18:23:28 -0700
Subject: [PATCH] Optimise ArraySetSorted#removeIf

Remove iterator allocation and ensure the call is always O(n)

diff --git a/src/main/java/net/minecraft/util/SortedArraySet.java b/src/main/java/net/minecraft/util/SortedArraySet.java
index d1b2ba24ef54e01c6249c3b2ca16e80f03c001a6..5f1c4c6b9e36f2d6ec43b82cc0e2cae24b800dc4 100644
--- a/src/main/java/net/minecraft/util/SortedArraySet.java
+++ b/src/main/java/net/minecraft/util/SortedArraySet.java
@@ -22,6 +22,41 @@ public class SortedArraySet<T> extends AbstractSet<T> {
             this.contents = (T[])castRawArray(new Object[initialCapacity]);
         }
     }
+    // Paper start - optimise removeIf
+    @Override
+    public boolean removeIf(java.util.function.Predicate<? super T> filter) {
+        // prev. impl used an iterator, which could be n^2 and creates garbage
+        int i = 0, len = this.size;
+        T[] backingArray = this.contents;
+
+        for (;;) {
+            if (i >= len) {
+                return false;
+            }
+            if (!filter.test(backingArray[i])) {
+                ++i;
+                continue;
+            }
+            break;
+        }
+
+        // we only want to write back to backingArray if we really need to
+
+        int lastIndex = i; // this is where new elements are shifted to
+
+        for (; i < len; ++i) {
+            T curr = backingArray[i];
+            if (!filter.test(curr)) { // if test throws we're screwed
+                backingArray[lastIndex++] = curr;
+            }
+        }
+
+        // cleanup end
+        Arrays.fill(backingArray, lastIndex, len, null);
+        this.size = lastIndex;
+        return true;
+    }
+    // Paper end - optimise removeIf
 
     public static <T extends Comparable<T>> SortedArraySet<T> create() {
         return create(10);