PaperMC/patches/server/0406-Fix-missing-chunks-due-to-integer-overflow.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: David Slovikosky <davidslovikosky@gmail.com>
Date: Tue, 9 Jun 2020 00:10:03 -0700
Subject: [PATCH] Fix missing chunks due to integer overflow

This patch fixes a bug in the EndIslandDensityFunction class where the distance
from 0,0 squared overflows the maximum size of an integer. The overflow leads
to hard chunk borders around 370,000 blocks from 0,0. After this cutoff there
is a few hundred thousand block gap before end land resuming to generate at
530,000 blocks from spawn. This is due to the integer flipping back and forth.

The fix for the issue is quite simple, casting chunk coordinates to longs
allows the distance calculation to avoid overflow and work as intended.

This issue is being tracked in Mojira ticket MC-159283

diff --git a/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java b/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java
index 299116c5c4d25c78a2af00bb44c4f51ac04286e8..fac92f37c32e0398ebc05d9a0378446fcabaef1a 100644
--- a/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java
+++ b/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java
@@ -502,7 +502,7 @@ public final class DensityFunctions {
             int j = z / 2;
             int k = x % 2;
             int l = z % 2;
-            float f = 100.0F - Mth.sqrt((float)(x * x + z * z)) * 8.0F;
+            float f = 100.0F - Mth.sqrt((long) x * (long) x + (long) z * (long) z) * 8.0F; // Paper - cast ints to long to avoid integer overflow
             f = Mth.clamp(f, -100.0F, 80.0F);
 
             for(int m = -12; m <= 12; ++m) {