Handle pre-1.16 chunks in forge 1.16+

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);
+        }
+    }
+}