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 db1d0e5cec19059d14e1a7cd41f049d23600e3fe..92c2df6a6abd9c60e90b0b84ab66987557adb9c8 100644
--- a/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java
+++ b/src/main/java/net/minecraft/world/level/levelgen/DensityFunctions.java
@@ -521,7 +521,7 @@ 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++) {