proper migration to gamerules for keep spawn loaded distance

patches/server/0377-Fix-missing-chunks-due-to-integer-overflow.patch

@@ -0,0 +1,29 @@
+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 6171d57a0e5d1aecadfb2c23a72a92d897ca41ee..b09bc1dac649ce9f4826edc1923c843804226993 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++) {