From 60a23a04c83c1561af668351d85323ecb635b906 Mon Sep 17 00:00:00 2001
From: Mike Primm <mike@primmhome.com>
Date: Sat, 15 Aug 2020 19:29:29 -0500
Subject: [PATCH] Handle pre-1.16 chunks in forge 1.16+

---
 .../java/org/dynmap/utils/DataBitsPacked.java | 53 +++++++++++++++++++
 .../dynmap/forge_1_16_1/ChunkSnapshot.java    | 18 +++++--
 2 files changed, 67 insertions(+), 4 deletions(-)
 create mode 100644 DynmapCore/src/main/java/org/dynmap/utils/DataBitsPacked.java

diff --git a/DynmapCore/src/main/java/org/dynmap/utils/DataBitsPacked.java b/DynmapCore/src/main/java/org/dynmap/utils/DataBitsPacked.java
new file mode 100644
index 00000000..3f4b62f6
--- /dev/null
+++ b/DynmapCore/src/main/java/org/dynmap/utils/DataBitsPacked.java
@@ -0,0 +1,53 @@
+package org.dynmap.utils;
+
+// Pre 1.16 chunk section data array
+public class DataBitsPacked {
+
+    private final long[] values;
+    private final int bitsperrec;
+    private final long valuemask;
+    private final int length;
+
+    public static int calcLongCount(int i, int j) {
+        if (j == 0) {
+            return 0;
+        } else if (i == 0) {
+            return j;
+        } else {
+            if (i < 0) {
+                j *= -1;
+            }
+
+            int k = i % j;
+
+            return k == 0 ? i : i + j - k;
+        }
+    }
+
+    public DataBitsPacked(int bitsperrec, int length, long[] values) {
+        this.length = length;
+        this.bitsperrec = bitsperrec;
+        this.values = values;
+        this.valuemask = (1L << bitsperrec) - 1L;
+        int properlength = calcLongCount(length * bitsperrec, 64) / 64;
+
+        if (values.length != properlength) {
+            throw new IllegalArgumentException("Invalid length given for storage, got: " + values.length + " but expected: " + properlength);
+        }
+    }
+
+    public int getAt(int offset) {
+        int j = offset * this.bitsperrec;
+        int k = j >> 6;
+        int l = (offset + 1) * this.bitsperrec - 1 >> 6;
+        int i1 = j ^ k << 6;
+
+        if (k == l) {
+            return (int) (this.values[k] >>> i1 & this.valuemask);
+        } else {
+            int j1 = 64 - i1;
+
+            return (int) ((this.values[k] >>> i1 | this.values[l] << j1) & this.valuemask);
+        }
+    }
+}
diff --git a/forge-1.16.1/src/main/java/org/dynmap/forge_1_16_1/ChunkSnapshot.java b/forge-1.16.1/src/main/java/org/dynmap/forge_1_16_1/ChunkSnapshot.java
index 4332968c..0c95a65a 100644
--- a/forge-1.16.1/src/main/java/org/dynmap/forge_1_16_1/ChunkSnapshot.java
+++ b/forge-1.16.1/src/main/java/org/dynmap/forge_1_16_1/ChunkSnapshot.java
@@ -4,6 +4,7 @@ import java.util.Arrays;
 
 import org.dynmap.Log;
 import org.dynmap.renderer.DynmapBlockState;
+import org.dynmap.utils.DataBitsPacked;
 
 import net.minecraft.nbt.CompoundNBT;
 import net.minecraft.nbt.ListNBT;
@@ -178,16 +179,25 @@ public class ChunkSnapshot
                         palette[pi] = DynmapBlockState.AIR;
                     }
                 }
-                int bitsperblock = (statelist.length * 64) / 4096;
-                BitArray db = new BitArray(bitsperblock, 4096, statelist);
+            	int recsperblock = (4096 + statelist.length - 1) / statelist.length;
+            	int bitsperblock = 64 / recsperblock;
+            	BitArray db = null;
+            	DataBitsPacked dbp = null;
+            	try {
+            		db = new BitArray(bitsperblock, 4096, statelist);
+            	} catch (Exception x) {	// Handle legacy encoded
+	            	bitsperblock = (statelist.length * 64) / 4096;
+            		dbp = new DataBitsPacked(bitsperblock, 4096, statelist);
+            	}
                 if (bitsperblock > 8) {	// Not palette
                     for (int j = 0; j < 4096; j++) {
-                        states[j] = DynmapBlockState.getStateByGlobalIndex(db.getAt(j));
+                    	int v = (dbp != null) ? dbp.getAt(j) : db.getAt(j);
+                        states[j] = DynmapBlockState.getStateByGlobalIndex(v);
                     }
                 }
                 else {
                     for (int j = 0; j < 4096; j++) {
-                        int v = db.getAt(j);
+                    	int v = (dbp != null) ? dbp.getAt(j) : db.getAt(j);
                         states[j] = (v < palette.length) ? palette[v] : DynmapBlockState.AIR;
                     }
                 }