comp500/SectionCopyBenchmark.java

## SectionCopyBenchmark.java
package org.example;

import sun.misc.Unsafe;
import org.openjdk.jmh.annotations.*;

import java.lang.invoke.MethodHandles;
import java.lang.invoke.VarHandle;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.LongBuffer;
import java.util.Arrays;
import java.util.Random;

@Fork(value = 1, jvmArgsAppend = {
	"--add-exports",
	"java.base/jdk.internal.misc=ALL-UNNAMED",
	"-XX:+UseSuperWord",
	"-XX:+UnlockDiagnosticVMOptions",
	"-XX:CompileCommand=print,*SectionCopyBenchmark.copyShift2D"})
@Warmup(iterations = 5)
@Measurement(iterations = 10)
public class SectionCopyBenchmark {

	private static class BlockState {}

	@State(Scope.Thread)
	public static class Context {
		public final BlockState[] dest = new BlockState[4096];
		public final BlockState[] palette = new BlockState[16];
		public final long[] src = new long[256];
		public final int[] destIndexes = new int[4096];
		public final long[] shifts = new long[4096];
		public final long[] destIndexesLong = new long[4096];
		public final int[] destIndexesInt = new int[4096];
		public final LongBuffer destIndexesLongOffHeap = ByteBuffer.allocateDirect(4096 * 8).asLongBuffer();
		public final LongBuffer destIndexesLongOnHeap = LongBuffer.allocate(4096);
		public final byte[] destIndexesByte = new byte[4096 * 8];
		public long startAddr = 0;
		public final long[][] destIndexesLong2D = new long[16][256];

		@Setup
		public void setup() throws ClassNotFoundException, InvocationTargetException, IllegalAccessException, NoSuchMethodException {
			Arrays.fill(dest, null);
			for (int i = 0; i < palette.length; i++) {
				palette[i] = new BlockState();
			}
			Random random = new Random();
			long prev = random.nextLong();
			for (int i = 0; i < src.length; i++) {
				if (random.nextBoolean()) {
					src[i] = random.nextLong();
					prev = src[i];
				} else {
					src[i] = prev;
				}
			}

			for (int i = 0; i < shifts.length; i += 16) {
				for (int j = 0; j < 64; j += 4, i++) {
					shifts[i] = 1L << j;
				}
			}

//			Method address = Class.forName("sun.nio.ch.DirectBuffer").getMethod("address");
//			startAddr = (long) address.invoke(destIndexesLongOffHeap);
		}
	}

	/*
	With random data:
	Benchmark                       Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.unrolled  thrpt   10  184724.725 ± 1339.400  ops/s
	With all zeros:
	Benchmark                       Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.unrolled  thrpt   10  184770.122 ± 1621.971  ops/s
	 */
	@Benchmark
	public BlockState[] unrolled(Context context) {
		long[] data = context.src;
		BlockState[] palette = context.palette;
		BlockState[] dst = context.dest;

		for (int i = 0, blockIdx = 0; i < data.length; i++, blockIdx += 16) {
			long v = data[i];
			dst[blockIdx]      = palette[(int) (v          & 15)];
			dst[blockIdx + 1]  = palette[(int) ((v >>> 4 ) & 15)];
			dst[blockIdx + 2]  = palette[(int) ((v >>> 8 ) & 15)];
			dst[blockIdx + 3]  = palette[(int) ((v >>> 12) & 15)];
			dst[blockIdx + 4]  = palette[(int) ((v >>> 16) & 15)];
			dst[blockIdx + 5]  = palette[(int) ((v >>> 20) & 15)];
			dst[blockIdx + 6]  = palette[(int) ((v >>> 24) & 15)];
			dst[blockIdx + 7]  = palette[(int) ((v >>> 28) & 15)];
			dst[blockIdx + 8]  = palette[(int) ((v >>> 32) & 15)];
			dst[blockIdx + 9]  = palette[(int) ((v >>> 36) & 15)];
			dst[blockIdx + 10] = palette[(int) ((v >>> 40) & 15)];
			dst[blockIdx + 11] = palette[(int) ((v >>> 44) & 15)];
			dst[blockIdx + 12] = palette[(int) ((v >>> 48) & 15)];
			dst[blockIdx + 13] = palette[(int) ((v >>> 52) & 15)];
			dst[blockIdx + 14] = palette[(int) ((v >>> 56) & 15)];
			dst[blockIdx + 15] = palette[(int) ((v >>> 60) & 15)];
		}

		return context.dest;
	}

	/*
	With random data:
	Benchmark                            Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.prevArraycopy  thrpt   10  105549.357 ± 3117.402  ops/s
	With 50% repeated data:
	Benchmark                            Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.prevArraycopy  thrpt   10  107347.234 ± 4216.832  ops/s
	With all zeros:
	Benchmark                            Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.prevArraycopy  thrpt   10  127338.287 ± 2165.085  ops/s
	 */
	@Benchmark
	public BlockState[] prevArraycopy(Context context) {
		long[] data = context.src;
		BlockState[] palette = context.palette;
		BlockState[] dst = context.dest;

		int blockIdx = 0;
		long v = data[0], prevV = data[0];
		for (int shift = 0; shift < 64; shift += 4, blockIdx++) {
			dst[blockIdx] = palette[(int) ((v >>> shift) & 15)];
		}
		for (int i = 1; i < data.length; i++) {
			v = data[i];
			if (v == prevV) {
				System.arraycopy(dst, blockIdx - 16, dst, blockIdx, 16);
				blockIdx += 16;
			} else {
				prevV = v;
				for (int shift = 0; shift < 64; shift += 4, blockIdx++) {
					dst[blockIdx] = palette[(int) ((v >>> shift) & 15)];
				}
			}
		}

		return context.dest;
	}

	/*
	With all zeros:
	Benchmark                         Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.simpleLoop  thrpt   10  130528.025 ± 1449.589  ops/s
	With 50% repeated data:
	Benchmark                         Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.simpleLoop  thrpt   10  128406.166 ± 7226.141  ops/s
	 */
	@Benchmark
	public BlockState[] simpleLoop(Context context) {
		long[] data = context.src;
		BlockState[] palette = context.palette;
		BlockState[] dst = context.dest;

		for (int i = 0, blockIdx = 0; i < data.length; i++) {
			long v = data[i];
			for (int j = 0; j < 64; j += 4, blockIdx++) {
				dst[blockIdx] = palette[(int) ((v >>> j) & 15)];
			}
		}

		return context.dest;
	}

	/*
	With 50% repeated data:
	Benchmark                             Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.bytewise        thrpt   10  130926.419 ± 3423.496  ops/s
	 */
	@Benchmark
	public BlockState[] bytewise(Context context) {
		long[] data = context.src;
		BlockState[] palette = context.palette;
		BlockState[] dst = context.dest;

		for (int i = 0, blockIdx = 0; i < data.length; i++) {
			long v = data[i];
			for (int j = 0; j < 64; j += 8, blockIdx += 2) {
				byte b = (byte) (v >>> j);
				dst[blockIdx] =     palette[b         & 15];
				dst[blockIdx + 1] = palette[(b >>> 4) & 15];
			}
		}

		return context.dest;
	}

	/*
	50% repeated data:
	Benchmark                              Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.bytewiseIndexes  thrpt   10  377116.340 ± 3399.245  ops/s
	 */
	@Benchmark
	public int[] bytewiseIndexes(Context context) {
		long[] data = context.src;
		int[] dst = context.destIndexes;

		for (int i = 0, blockIdx = 0; i < data.length; i++) {
			long v = data[i];
			for (int j = 0; j < 64; j += 8, blockIdx += 2) {
				byte b = (byte) (v >>> j);
				dst[blockIdx] =     b & 15;
				dst[blockIdx + 1] = (b >>> 4) & 15;
			}
		}

		return context.destIndexes;
	}

	/*
	50% repeated data:
	Benchmark                                Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.simpleLoopIndexes  thrpt   10  329252.592 ± 2189.486  ops/s
	 */
	@Benchmark
	public int[] simpleLoopIndexes(Context context) {
		long[] data = context.src;
		int[] dst = context.destIndexes;

		for (int i = 0, blockIdx = 0; i < data.length; i++) {
			long v = data[i];
			for (int j = 0; j < 64; j += 4, blockIdx++) {
				dst[blockIdx] = (int) ((v >>> j) & 15);
			}
		}

		return context.destIndexes;
	}

	/*
	50% repeated data:
	Benchmark                              Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.unrolledIndexes  thrpt   10  394397.562 ± 2150.307  ops/s
	 */
	@Benchmark
	public int[] unrolledIndexes(Context context) {
		long[] data = context.src;
		int[] dst = context.destIndexes;

		for (int i = 0, blockIdx = 0; i < data.length; i++, blockIdx += 16) {
			long v = data[i];
			dst[blockIdx]      = (int) (v          & 15);
			dst[blockIdx + 1]  = (int) ((v >>> 4 ) & 15);
			dst[blockIdx + 2]  = (int) ((v >>> 8 ) & 15);
			dst[blockIdx + 3]  = (int) ((v >>> 12) & 15);
			dst[blockIdx + 4]  = (int) ((v >>> 16) & 15);
			dst[blockIdx + 5]  = (int) ((v >>> 20) & 15);
			dst[blockIdx + 6]  = (int) ((v >>> 24) & 15);
			dst[blockIdx + 7]  = (int) ((v >>> 28) & 15);
			dst[blockIdx + 8]  = (int) ((v >>> 32) & 15);
			dst[blockIdx + 9]  = (int) ((v >>> 36) & 15);
			dst[blockIdx + 10] = (int) ((v >>> 40) & 15);
			dst[blockIdx + 11] = (int) ((v >>> 44) & 15);
			dst[blockIdx + 12] = (int) ((v >>> 48) & 15);
			dst[blockIdx + 13] = (int) ((v >>> 52) & 15);
			dst[blockIdx + 14] = (int) ((v >>> 56) & 15);
			dst[blockIdx + 15] = (int) ((v >>> 60) & 15);
		}

		return context.destIndexes;
	}

	// Note: doesn't do mask!
	/*
	With 50% repeated data:
	Benchmark                                  Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.preCalculatedShifts  thrpt   10  462235.488 ± 6357.533  ops/s
	 */
	@Benchmark
	public long[] preCalculatedShifts(Context context) {
		long[] data = context.src;
		long[] shifts = context.shifts;
		long[] dst = context.destIndexesLong;

		for (int blockIdx = 0; blockIdx < dst.length; blockIdx += 16) {
			long v = data[blockIdx >>> 4];
			dst[blockIdx]     = v >>> shifts[blockIdx];
			dst[blockIdx + 1] = v >>> shifts[blockIdx + 1];
			dst[blockIdx + 2] = v >>> shifts[blockIdx + 2];
			dst[blockIdx + 3] = v >>> shifts[blockIdx + 3];
			dst[blockIdx + 4] = v >>> shifts[blockIdx + 4];
			dst[blockIdx + 5] = v >>> shifts[blockIdx + 5];
			dst[blockIdx + 6] = v >>> shifts[blockIdx + 6];
			dst[blockIdx + 7] = v >>> shifts[blockIdx + 7];
			dst[blockIdx + 8] = v >>> shifts[blockIdx + 8];
			dst[blockIdx + 9] = v >>> shifts[blockIdx + 9];
			dst[blockIdx + 10] = v >>> shifts[blockIdx + 10];
			dst[blockIdx + 11] = v >>> shifts[blockIdx + 11];
			dst[blockIdx + 12] = v >>> shifts[blockIdx + 12];
			dst[blockIdx + 13] = v >>> shifts[blockIdx + 13];
			dst[blockIdx + 14] = v >>> shifts[blockIdx + 14];
			dst[blockIdx + 15] = v >>> shifts[blockIdx + 15];
		}

		return dst;
	}

	// Note: changes layout of destIndexesLong... also doesn't work! It copies the data over the same location...
	/*
	50% repeated data, SIMD enabled:
	Benchmark                                   Mode  Cnt        Score       Error  Units
	SectionCopyBenchmark.constantShiftLoops2D  thrpt   10  1862705.797 ± 51227.373  ops/s
	50% repeated data, SIMD disabled:
	Benchmark                                   Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.constantShiftLoops2D  thrpt   10  513844.888 ± 2668.240  ops/s
	 */
	@Benchmark
	public long[] constantShiftLoops(Context context) {
		long[] data = context.src;
		long[] dst = context.destIndexesLong;

		for (int i = 0; i < 16; i++) {
			copyShift(data, dst, i << 2, 15L << (i << 2));
		}

		return dst;
	}

	private static void copyShift(long[] data, long[] dst, long shift, long mask) {
		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
			// This isn't the right offset, and adding an offset makes the JVM not autovectorise it
			dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
		}
	}

	// Note: changes layout of destIndexesInt
	/*
	This one doesn't get autovectorised :(
	50% repeated data:
	Benchmark                                    Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.constantShiftLoopsInt  thrpt   10  438808.426 ± 3617.427  ops/s
	 */
	@Benchmark
	public int[] constantShiftLoopsInt(Context context) {
		long[] data = context.src;
		int[] dst = context.destIndexesInt;

		for (int i = 0; i < 16; i++) {
			copyShiftInt(data, dst, i << 2, 15L << (i << 2));
		}

		return dst;
	}

	private static void copyShiftInt(long[] data, int[] dst, long shift, long mask) {
		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
			dst[blockIdx] = (int) ((data[blockIdx] & mask) >>> shift);
		}
	}

	private static final Unsafe UNSAFE;

	static {
		try {
			Field field = Unsafe.class.getDeclaredField("theUnsafe");
			field.setAccessible(true);

			UNSAFE = (Unsafe) field.get(null);
		} catch (IllegalAccessException | NoSuchFieldException e) {
			throw new RuntimeException(e);
		}
	}

	/*
	Doesn't get autovectorised!
	 */
//	@Benchmark
//	public long[] constantShiftLoopsUnsafe(Context context) {
//		long[] data = context.src;
//		long[] dst = context.destIndexesLong;
//
//		long addr = context.startAddr;
//
//		for (int i = 0; i < 16; i++) {
//			copyShiftUnsafe(i << 2, 15L << (i << 2), addr + (i * 256 * 8));
//		}
//
//		return dst;
//	}
//
//	private static void copyShiftUnsafe(long shift, long mask, long addr) {
//		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
//			//UNSAFE.putLong(addr + (blockIdx * 8), data[blockIdx] & mask >>> shift);
//			UNSAFE.putLong(addr + (blockIdx * 8), (UNSAFE.getLong(addr + (blockIdx * 8)) & mask) >>> shift);
//		}
//	}

	final static VarHandle VH_arr_view = MethodHandles.byteArrayViewVarHandle(long[].class, ByteOrder.nativeOrder());

	/*
	Doesn't get autovectorised!
	 */
	@Benchmark
	public byte[] constantShiftLoopsVarHandle(Context context) {
		long[] data = context.src;
		byte[] dst = context.destIndexesByte;

		for (int i = 0; i < 16; i++) {
			copyShiftVarHandle(data, dst, i << 2, 15L << (i << 2));
		}

		return dst;
	}

	private static void copyShiftVarHandle(long[] data, byte[] dst, long shift, long mask) {
		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
			VH_arr_view.set(dst, blockIdx, (data[blockIdx] & mask) >>> shift);
		}
	}

	/*
	Doesn't get autovectorised!
	 */
	@Benchmark
	public LongBuffer constantShiftLoopsBuf(Context context) {
		long[] data = context.src;
		LongBuffer dst = context.destIndexesLongOnHeap;

		for (int i = 0; i < 16; i++) {
			copyShiftBuf(data, i << 2, 15L << (i << 2), dst);
		}

		return dst;
	}

	private static void copyShiftBuf(long[] data, long shift, long mask, LongBuffer dst) {
		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
			dst.put(blockIdx, (data[blockIdx] & mask) >>> shift);
		}
	}

	/*
	50% repeated data, SIMD enabled:
	Benchmark                                   Mode  Cnt        Score       Error  Units
	SectionCopyBenchmark.constantShiftLoops2D  thrpt   10  1867600.924 ± 51025.923  ops/s
	50% repeated data, SIMD disabled:
	Benchmark                                   Mode  Cnt       Score      Error  Units
	SectionCopyBenchmark.constantShiftLoops2D  thrpt   10  513538.086 ± 2510.975  ops/s
	 */
	@Benchmark
	public long[][] constantShiftLoops2D(Context context) {
		long[] data = context.src;
		long[][] dst = context.destIndexesLong2D;

		for (int i = 0; i < 16; i++) {
			copyShift2D(data, dst[i], i << 2, 15L << (i << 2));
		}

		return dst;
	}

	private static void copyShift2D(long[] data, long[] dst, long shift, long mask) {
		for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
			dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
		}
	}

	/*
	50% repeated data, SIMD enabled, [0, 256):
	Benchmark                                          Mode  Cnt        Score      Error  Units
	SectionCopyBenchmark.constantShiftLoops2DSection  thrpt   10  1790481.403 ± 9363.477  ops/s
	50% repeated data, SIMD enabled, [0, 128) then [128, 256):
	Benchmark                                          Mode  Cnt        Score       Error  Units
	SectionCopyBenchmark.constantShiftLoops2DSection  thrpt   10  1687734.486 ± 24420.654  ops/s
	50% repeated data, SIMD enabled, [0, 128):
	Benchmark                                          Mode  Cnt        Score       Error  Units
	SectionCopyBenchmark.constantShiftLoops2DSection  thrpt   10  3517598.227 ± 16300.049  ops/s
	 */
	@Benchmark
	public long[][] constantShiftLoops2DSection(Context context) {
		long[] data = context.src;
		long[][] dst = context.destIndexesLong2D;

		for (int i = 0; i < 16; i++) {
			copyShift2D(data, dst[i], i << 2, 15L << (i << 2), 0, 128);
		}

		return dst;
	}

	private static void copyShift2D(long[] data, long[] dst, long shift, long mask, int start, int end) {
		for (int blockIdx = start; blockIdx < end; blockIdx += 1) {
			dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
		}
	}

}
	package org.example;

	import sun.misc.Unsafe;
	import org.openjdk.jmh.annotations.*;

	import java.lang.invoke.MethodHandles;
	import java.lang.invoke.VarHandle;
	import java.lang.reflect.Field;
	import java.lang.reflect.InvocationTargetException;
	import java.lang.reflect.Method;
	import java.nio.ByteBuffer;
	import java.nio.ByteOrder;
	import java.nio.LongBuffer;
	import java.util.Arrays;
	import java.util.Random;

	@Fork(value = 1, jvmArgsAppend = {
	"--add-exports",
	"java.base/jdk.internal.misc=ALL-UNNAMED",
	"-XX:+UseSuperWord",
	"-XX:+UnlockDiagnosticVMOptions",
	"-XX:CompileCommand=print,*SectionCopyBenchmark.copyShift2D"})
	@Warmup(iterations = 5)
	@Measurement(iterations = 10)
	public class SectionCopyBenchmark {

	private static class BlockState {}

	@State(Scope.Thread)
	public static class Context {
	public final BlockState[] dest = new BlockState[4096];
	public final BlockState[] palette = new BlockState[16];
	public final long[] src = new long[256];
	public final int[] destIndexes = new int[4096];
	public final long[] shifts = new long[4096];
	public final long[] destIndexesLong = new long[4096];
	public final int[] destIndexesInt = new int[4096];
	public final LongBuffer destIndexesLongOffHeap = ByteBuffer.allocateDirect(4096 * 8).asLongBuffer();
	public final LongBuffer destIndexesLongOnHeap = LongBuffer.allocate(4096);
	public final byte[] destIndexesByte = new byte[4096 * 8];
	public long startAddr = 0;
	public final long[][] destIndexesLong2D = new long[16][256];

	@Setup
	public void setup() throws ClassNotFoundException, InvocationTargetException, IllegalAccessException, NoSuchMethodException {
	Arrays.fill(dest, null);
	for (int i = 0; i < palette.length; i++) {
	palette[i] = new BlockState();
	}
	Random random = new Random();
	long prev = random.nextLong();
	for (int i = 0; i < src.length; i++) {
	if (random.nextBoolean()) {
	src[i] = random.nextLong();
	prev = src[i];
	} else {
	src[i] = prev;
	}
	}

	for (int i = 0; i < shifts.length; i += 16) {
	for (int j = 0; j < 64; j += 4, i++) {
	shifts[i] = 1L << j;
	}
	}

	// Method address = Class.forName("sun.nio.ch.DirectBuffer").getMethod("address");
	// startAddr = (long) address.invoke(destIndexesLongOffHeap);
	}
	}

	/*
	With random data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.unrolled thrpt 10 184724.725 ± 1339.400 ops/s
	With all zeros:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.unrolled thrpt 10 184770.122 ± 1621.971 ops/s
	*/
	@Benchmark
	public BlockState[] unrolled(Context context) {
	long[] data = context.src;
	BlockState[] palette = context.palette;
	BlockState[] dst = context.dest;

	for (int i = 0, blockIdx = 0; i < data.length; i++, blockIdx += 16) {
	long v = data[i];
	dst[blockIdx] = palette[(int) (v & 15)];
	dst[blockIdx + 1] = palette[(int) ((v >>> 4 ) & 15)];
	dst[blockIdx + 2] = palette[(int) ((v >>> 8 ) & 15)];
	dst[blockIdx + 3] = palette[(int) ((v >>> 12) & 15)];
	dst[blockIdx + 4] = palette[(int) ((v >>> 16) & 15)];
	dst[blockIdx + 5] = palette[(int) ((v >>> 20) & 15)];
	dst[blockIdx + 6] = palette[(int) ((v >>> 24) & 15)];
	dst[blockIdx + 7] = palette[(int) ((v >>> 28) & 15)];
	dst[blockIdx + 8] = palette[(int) ((v >>> 32) & 15)];
	dst[blockIdx + 9] = palette[(int) ((v >>> 36) & 15)];
	dst[blockIdx + 10] = palette[(int) ((v >>> 40) & 15)];
	dst[blockIdx + 11] = palette[(int) ((v >>> 44) & 15)];
	dst[blockIdx + 12] = palette[(int) ((v >>> 48) & 15)];
	dst[blockIdx + 13] = palette[(int) ((v >>> 52) & 15)];
	dst[blockIdx + 14] = palette[(int) ((v >>> 56) & 15)];
	dst[blockIdx + 15] = palette[(int) ((v >>> 60) & 15)];
	}

	return context.dest;
	}

	/*
	With random data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.prevArraycopy thrpt 10 105549.357 ± 3117.402 ops/s
	With 50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.prevArraycopy thrpt 10 107347.234 ± 4216.832 ops/s
	With all zeros:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.prevArraycopy thrpt 10 127338.287 ± 2165.085 ops/s
	*/
	@Benchmark
	public BlockState[] prevArraycopy(Context context) {
	long[] data = context.src;
	BlockState[] palette = context.palette;
	BlockState[] dst = context.dest;

	int blockIdx = 0;
	long v = data[0], prevV = data[0];
	for (int shift = 0; shift < 64; shift += 4, blockIdx++) {
	dst[blockIdx] = palette[(int) ((v >>> shift) & 15)];
	}
	for (int i = 1; i < data.length; i++) {
	v = data[i];
	if (v == prevV) {
	System.arraycopy(dst, blockIdx - 16, dst, blockIdx, 16);
	blockIdx += 16;
	} else {
	prevV = v;
	for (int shift = 0; shift < 64; shift += 4, blockIdx++) {
	dst[blockIdx] = palette[(int) ((v >>> shift) & 15)];
	}
	}
	}

	return context.dest;
	}

	/*
	With all zeros:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.simpleLoop thrpt 10 130528.025 ± 1449.589 ops/s
	With 50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.simpleLoop thrpt 10 128406.166 ± 7226.141 ops/s
	*/
	@Benchmark
	public BlockState[] simpleLoop(Context context) {
	long[] data = context.src;
	BlockState[] palette = context.palette;
	BlockState[] dst = context.dest;

	for (int i = 0, blockIdx = 0; i < data.length; i++) {
	long v = data[i];
	for (int j = 0; j < 64; j += 4, blockIdx++) {
	dst[blockIdx] = palette[(int) ((v >>> j) & 15)];
	}
	}

	return context.dest;
	}

	/*
	With 50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.bytewise thrpt 10 130926.419 ± 3423.496 ops/s
	*/
	@Benchmark
	public BlockState[] bytewise(Context context) {
	long[] data = context.src;
	BlockState[] palette = context.palette;
	BlockState[] dst = context.dest;

	for (int i = 0, blockIdx = 0; i < data.length; i++) {
	long v = data[i];
	for (int j = 0; j < 64; j += 8, blockIdx += 2) {
	byte b = (byte) (v >>> j);
	dst[blockIdx] = palette[b & 15];
	dst[blockIdx + 1] = palette[(b >>> 4) & 15];
	}
	}

	return context.dest;
	}

	/*
	50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.bytewiseIndexes thrpt 10 377116.340 ± 3399.245 ops/s
	*/
	@Benchmark
	public int[] bytewiseIndexes(Context context) {
	long[] data = context.src;
	int[] dst = context.destIndexes;

	for (int i = 0, blockIdx = 0; i < data.length; i++) {
	long v = data[i];
	for (int j = 0; j < 64; j += 8, blockIdx += 2) {
	byte b = (byte) (v >>> j);
	dst[blockIdx] = b & 15;
	dst[blockIdx + 1] = (b >>> 4) & 15;
	}
	}

	return context.destIndexes;
	}

	/*
	50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.simpleLoopIndexes thrpt 10 329252.592 ± 2189.486 ops/s
	*/
	@Benchmark
	public int[] simpleLoopIndexes(Context context) {
	long[] data = context.src;
	int[] dst = context.destIndexes;

	for (int i = 0, blockIdx = 0; i < data.length; i++) {
	long v = data[i];
	for (int j = 0; j < 64; j += 4, blockIdx++) {
	dst[blockIdx] = (int) ((v >>> j) & 15);
	}
	}

	return context.destIndexes;
	}

	/*
	50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.unrolledIndexes thrpt 10 394397.562 ± 2150.307 ops/s
	*/
	@Benchmark
	public int[] unrolledIndexes(Context context) {
	long[] data = context.src;
	int[] dst = context.destIndexes;

	for (int i = 0, blockIdx = 0; i < data.length; i++, blockIdx += 16) {
	long v = data[i];
	dst[blockIdx] = (int) (v & 15);
	dst[blockIdx + 1] = (int) ((v >>> 4 ) & 15);
	dst[blockIdx + 2] = (int) ((v >>> 8 ) & 15);
	dst[blockIdx + 3] = (int) ((v >>> 12) & 15);
	dst[blockIdx + 4] = (int) ((v >>> 16) & 15);
	dst[blockIdx + 5] = (int) ((v >>> 20) & 15);
	dst[blockIdx + 6] = (int) ((v >>> 24) & 15);
	dst[blockIdx + 7] = (int) ((v >>> 28) & 15);
	dst[blockIdx + 8] = (int) ((v >>> 32) & 15);
	dst[blockIdx + 9] = (int) ((v >>> 36) & 15);
	dst[blockIdx + 10] = (int) ((v >>> 40) & 15);
	dst[blockIdx + 11] = (int) ((v >>> 44) & 15);
	dst[blockIdx + 12] = (int) ((v >>> 48) & 15);
	dst[blockIdx + 13] = (int) ((v >>> 52) & 15);
	dst[blockIdx + 14] = (int) ((v >>> 56) & 15);
	dst[blockIdx + 15] = (int) ((v >>> 60) & 15);
	}

	return context.destIndexes;
	}

	// Note: doesn't do mask!
	/*
	With 50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.preCalculatedShifts thrpt 10 462235.488 ± 6357.533 ops/s
	*/
	@Benchmark
	public long[] preCalculatedShifts(Context context) {
	long[] data = context.src;
	long[] shifts = context.shifts;
	long[] dst = context.destIndexesLong;

	for (int blockIdx = 0; blockIdx < dst.length; blockIdx += 16) {
	long v = data[blockIdx >>> 4];
	dst[blockIdx] = v >>> shifts[blockIdx];
	dst[blockIdx + 1] = v >>> shifts[blockIdx + 1];
	dst[blockIdx + 2] = v >>> shifts[blockIdx + 2];
	dst[blockIdx + 3] = v >>> shifts[blockIdx + 3];
	dst[blockIdx + 4] = v >>> shifts[blockIdx + 4];
	dst[blockIdx + 5] = v >>> shifts[blockIdx + 5];
	dst[blockIdx + 6] = v >>> shifts[blockIdx + 6];
	dst[blockIdx + 7] = v >>> shifts[blockIdx + 7];
	dst[blockIdx + 8] = v >>> shifts[blockIdx + 8];
	dst[blockIdx + 9] = v >>> shifts[blockIdx + 9];
	dst[blockIdx + 10] = v >>> shifts[blockIdx + 10];
	dst[blockIdx + 11] = v >>> shifts[blockIdx + 11];
	dst[blockIdx + 12] = v >>> shifts[blockIdx + 12];
	dst[blockIdx + 13] = v >>> shifts[blockIdx + 13];
	dst[blockIdx + 14] = v >>> shifts[blockIdx + 14];
	dst[blockIdx + 15] = v >>> shifts[blockIdx + 15];
	}

	return dst;
	}

	// Note: changes layout of destIndexesLong... also doesn't work! It copies the data over the same location...
	/*
	50% repeated data, SIMD enabled:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2D thrpt 10 1862705.797 ± 51227.373 ops/s
	50% repeated data, SIMD disabled:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2D thrpt 10 513844.888 ± 2668.240 ops/s
	*/
	@Benchmark
	public long[] constantShiftLoops(Context context) {
	long[] data = context.src;
	long[] dst = context.destIndexesLong;

	for (int i = 0; i < 16; i++) {
	copyShift(data, dst, i << 2, 15L << (i << 2));
	}

	return dst;
	}

	private static void copyShift(long[] data, long[] dst, long shift, long mask) {
	for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	// This isn't the right offset, and adding an offset makes the JVM not autovectorise it
	dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
	}
	}

	// Note: changes layout of destIndexesInt
	/*
	This one doesn't get autovectorised :(
	50% repeated data:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoopsInt thrpt 10 438808.426 ± 3617.427 ops/s
	*/
	@Benchmark
	public int[] constantShiftLoopsInt(Context context) {
	long[] data = context.src;
	int[] dst = context.destIndexesInt;

	for (int i = 0; i < 16; i++) {
	copyShiftInt(data, dst, i << 2, 15L << (i << 2));
	}

	return dst;
	}

	private static void copyShiftInt(long[] data, int[] dst, long shift, long mask) {
	for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	dst[blockIdx] = (int) ((data[blockIdx] & mask) >>> shift);
	}
	}

	private static final Unsafe UNSAFE;

	static {
	try {
	Field field = Unsafe.class.getDeclaredField("theUnsafe");
	field.setAccessible(true);

	UNSAFE = (Unsafe) field.get(null);
	} catch (IllegalAccessException \| NoSuchFieldException e) {
	throw new RuntimeException(e);
	}
	}

	/*
	Doesn't get autovectorised!
	*/
	// @Benchmark
	// public long[] constantShiftLoopsUnsafe(Context context) {
	// long[] data = context.src;
	// long[] dst = context.destIndexesLong;
	//
	// long addr = context.startAddr;
	//
	// for (int i = 0; i < 16; i++) {
	// copyShiftUnsafe(i << 2, 15L << (i << 2), addr + (i * 256 * 8));
	// }
	//
	// return dst;
	// }
	//
	// private static void copyShiftUnsafe(long shift, long mask, long addr) {
	// for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	// //UNSAFE.putLong(addr + (blockIdx * 8), data[blockIdx] & mask >>> shift);
	// UNSAFE.putLong(addr + (blockIdx * 8), (UNSAFE.getLong(addr + (blockIdx * 8)) & mask) >>> shift);
	// }
	// }

	final static VarHandle VH_arr_view = MethodHandles.byteArrayViewVarHandle(long[].class, ByteOrder.nativeOrder());

	/*
	Doesn't get autovectorised!
	*/
	@Benchmark
	public byte[] constantShiftLoopsVarHandle(Context context) {
	long[] data = context.src;
	byte[] dst = context.destIndexesByte;

	for (int i = 0; i < 16; i++) {
	copyShiftVarHandle(data, dst, i << 2, 15L << (i << 2));
	}

	return dst;
	}

	private static void copyShiftVarHandle(long[] data, byte[] dst, long shift, long mask) {
	for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	VH_arr_view.set(dst, blockIdx, (data[blockIdx] & mask) >>> shift);
	}
	}

	/*
	Doesn't get autovectorised!
	*/
	@Benchmark
	public LongBuffer constantShiftLoopsBuf(Context context) {
	long[] data = context.src;
	LongBuffer dst = context.destIndexesLongOnHeap;

	for (int i = 0; i < 16; i++) {
	copyShiftBuf(data, i << 2, 15L << (i << 2), dst);
	}

	return dst;
	}

	private static void copyShiftBuf(long[] data, long shift, long mask, LongBuffer dst) {
	for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	dst.put(blockIdx, (data[blockIdx] & mask) >>> shift);
	}
	}

	/*
	50% repeated data, SIMD enabled:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2D thrpt 10 1867600.924 ± 51025.923 ops/s
	50% repeated data, SIMD disabled:
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2D thrpt 10 513538.086 ± 2510.975 ops/s
	*/
	@Benchmark
	public long[][] constantShiftLoops2D(Context context) {
	long[] data = context.src;
	long[][] dst = context.destIndexesLong2D;

	for (int i = 0; i < 16; i++) {
	copyShift2D(data, dst[i], i << 2, 15L << (i << 2));
	}

	return dst;
	}

	private static void copyShift2D(long[] data, long[] dst, long shift, long mask) {
	for (int blockIdx = 0; blockIdx < 256; blockIdx += 1) {
	dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
	}
	}

	/*
	50% repeated data, SIMD enabled, [0, 256):
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2DSection thrpt 10 1790481.403 ± 9363.477 ops/s
	50% repeated data, SIMD enabled, [0, 128) then [128, 256):
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2DSection thrpt 10 1687734.486 ± 24420.654 ops/s
	50% repeated data, SIMD enabled, [0, 128):
	Benchmark Mode Cnt Score Error Units
	SectionCopyBenchmark.constantShiftLoops2DSection thrpt 10 3517598.227 ± 16300.049 ops/s
	*/
	@Benchmark
	public long[][] constantShiftLoops2DSection(Context context) {
	long[] data = context.src;
	long[][] dst = context.destIndexesLong2D;

	for (int i = 0; i < 16; i++) {
	copyShift2D(data, dst[i], i << 2, 15L << (i << 2), 0, 128);
	}

	return dst;
	}

	private static void copyShift2D(long[] data, long[] dst, long shift, long mask, int start, int end) {
	for (int blockIdx = start; blockIdx < end; blockIdx += 1) {
	dst[blockIdx] = (data[blockIdx] & mask) >>> shift;
	}
	}

	}