Implement PackedIntArrayAccess

BlueMapCore/src/main/java/de/bluecolored/bluemap/core/mca/ChunkAnvil118.java

@@ -225,7 +225,7 @@ public class ChunkAnvil118 extends MCAChunk {
             if (skyLight.length < 2048 && skyLight.length > 0) skyLight = Arrays.copyOf(skyLight, 2048);
 
             this.bitsPerBlock = this.blocks.length >> 6; // available longs * 64 (bits per long) / 4096 (blocks per section) (floored result)
-            this.bitsPerBiome = Integer.SIZE - Integer.numberOfLeadingZeros(this.biomePalette.length - 1);
+            this.bitsPerBiome = MCAMath.ceilLog2(this.biomePalette.length);
         }
 
         private BlockState readBlockStatePaletteEntry(CompoundTag paletteEntry) {
@@ -298,4 +298,8 @@ public class ChunkAnvil118 extends MCAChunk {
         }
     }
 
+    private static PackedIntArrayAccess heightmap(int worldHeight, long[] data) {
+        return new PackedIntArrayAccess(MCAMath.ceilLog2(worldHeight + 1), data);
+    }
+
 }

BlueMapCore/src/main/java/de/bluecolored/bluemap/core/mca/MCAMath.java

@@ -71,4 +71,8 @@ public class MCAMath {
         return value;
     }
 
+    public static int ceilLog2(int n) {
+        return Integer.SIZE - Integer.numberOfLeadingZeros(n - 1);
+    }
+
 }

BlueMapCore/src/main/java/de/bluecolored/bluemap/core/mca/PackedIntArrayAccess.java

@@ -0,0 +1,103 @@
+package de.bluecolored.bluemap.core.mca;
+
+public class PackedIntArrayAccess {
+    private static final int[] INDEX_PARAMETERS = new int[]{
+            -1, -1, 0,
+            Integer.MIN_VALUE, 0, 0,
+            1431655765, 1431655765, 0,
+            Integer.MIN_VALUE, 0, 1,
+            858993459, 858993459, 0,
+            715827882, 715827882, 0,
+            613566756, 613566756, 0,
+            Integer.MIN_VALUE, 0, 2,
+            477218588, 477218588, 0,
+            429496729, 429496729, 0,
+            390451572, 390451572, 0,
+            357913941, 357913941, 0,
+            330382099, 330382099, 0,
+            306783378, 306783378, 0,
+            286331153, 286331153, 0,
+            Integer.MIN_VALUE, 0, 3,
+            252645135, 252645135, 0,
+            238609294, 238609294, 0,
+            226050910, 226050910, 0,
+            214748364, 214748364, 0,
+            204522252, 204522252, 0,
+            195225786, 195225786, 0,
+            186737708, 186737708, 0,
+            178956970, 178956970, 0,
+            171798691, 171798691, 0,
+            165191049, 165191049, 0,
+            159072862, 159072862, 0,
+            153391689, 153391689, 0,
+            148102320, 148102320, 0,
+            143165576, 143165576, 0,
+            138547332, 138547332, 0,
+            Integer.MIN_VALUE, 0, 4,
+            130150524, 130150524, 0,
+            126322567, 126322567, 0,
+            122713351, 122713351, 0,
+            119304647, 119304647, 0,
+            116080197, 116080197, 0,
+            113025455, 113025455, 0,
+            110127366, 110127366, 0,
+            107374182, 107374182, 0,
+            104755299, 104755299, 0,
+            102261126, 102261126, 0,
+            99882960, 99882960, 0,
+            97612893, 97612893, 0,
+            95443717, 95443717, 0,
+            93368854, 93368854, 0,
+            91382282, 91382282, 0,
+            89478485, 89478485, 0,
+            87652393, 87652393, 0,
+            85899345, 85899345, 0,
+            84215045, 84215045, 0,
+            82595524, 82595524, 0,
+            81037118, 81037118, 0,
+            79536431, 79536431, 0,
+            78090314, 78090314, 0,
+            76695844, 76695844, 0,
+            75350303, 75350303, 0,
+            74051160, 74051160, 0,
+            72796055, 72796055, 0,
+            71582788, 71582788, 0,
+            70409299, 70409299, 0,
+            69273666, 69273666, 0,
+            68174084, 68174084, 0,
+            Integer.MIN_VALUE, 0, 5
+    };
+
+    private final int bitsPerElement;
+    private final long[] data;
+
+    private final long maxValue;
+    private final int elementsPerLong, indexScale, indexOffset, indexShift;
+
+    public PackedIntArrayAccess(int bitsPerElement, long[] data) {
+        this.bitsPerElement = bitsPerElement;
+        this.data = data;
+
+        this.maxValue = (1L << this.bitsPerElement) - 1L;
+        this.elementsPerLong = (char)(64 / this.bitsPerElement);
+
+        int i = 3 * (this.elementsPerLong - 1);
+        this.indexScale = INDEX_PARAMETERS[i];
+        this.indexOffset = INDEX_PARAMETERS[i + 1];
+        this.indexShift = INDEX_PARAMETERS[i + 2];
+    }
+
+    public int get(int i) {
+        int j = this.storageIndex(i);
+        long l = this.data[j];
+        int k = (i - j * this.elementsPerLong) * this.bitsPerElement;
+        return (int)(l >> k & this.maxValue);
+    }
+
+    public int storageIndex(int i) {
+        long l = Integer.toUnsignedLong(this.indexScale);
+        long m = Integer.toUnsignedLong(this.indexOffset);
+        return (int) ((long) i * l + m >> 32 >> this.indexShift);
+    }
+
+}