src/main/java/com/android/tools/r8/androidapi/AndroidApiDataAccess.java - r8.git - Git at Google

 // Copyright (c) 2022, the R8 project authors. Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.

 package com.android.tools.r8.androidapi;

 import static com.android.tools.r8.lightir.ByteUtils.unsetBitAtIndex;
 import static com.android.tools.r8.utils.ZipUtils.getOffsetOfResourceInZip;

 import com.android.tools.r8.DiagnosticsHandler;
 import com.android.tools.r8.dex.CompatByteBuffer;
 import com.android.tools.r8.errors.Unreachable;
 import com.android.tools.r8.graph.DexReference;
 import com.android.tools.r8.graph.DexString;
 import com.android.tools.r8.utils.ExceptionDiagnostic;
 import com.android.tools.r8.utils.InternalOptions;
 import com.android.tools.r8.utils.StringDiagnostic;
 import com.google.common.io.ByteStreams;
 import com.google.common.primitives.Ints;
 import java.io.File;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.JarURLConnection;
 import java.net.URL;
 import java.nio.MappedByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.nio.file.StandardOpenOption;
 import java.util.function.BiPredicate;

 /**
  * Implements low-level access methods for seeking on top of the database file defined by {@code
  * AndroidApiLevelHashingDatabaseImpl} where a description of the format can also be found.
  */
 public abstract class AndroidApiDataAccess {

   private static final String RESOURCE_NAME = "resources/new_api_database.ser";
   private static final int ENTRY_SIZE_IN_BITS_FOR_CONSTANT_POOL_MAP = 17;
   private static final int ENTRY_SIZE_IN_BITS_FOR_API_MAP = 18;
   // The payload offset is an offset into the payload defined by an integer and a length defined by
   // a short.
   private static final int PAYLOAD_OFFSET_WITH_LENGTH = 4 + 2;
   private static final byte ZERO_BYTE = (byte) 0;

   public static boolean isApiDatabaseEntry(String entry) {
     return RESOURCE_NAME.equals(entry);
   }

   private static class PositionAndLength {

     private static final PositionAndLength EMPTY = new PositionAndLength(0, 0);

     private final int position;
     private final int length;

     private PositionAndLength(int position, int length) {
       this.position = position;
       this.length = length;
     }

     public static PositionAndLength create(int position, int length) {
       if (position == 0 && length == 0) {
         return EMPTY;
       }
       if ((position < 0 && length > 0) || (position > 0 && length == 0)) {
         assert false : "Unexpected position and length";
         return EMPTY;
       }
       return new PositionAndLength(position, length);
     }

     public static PositionAndLength create(byte[] data, int offset) {
       return create(readIntFromOffset(data, offset), readShortFromOffset(data, offset + 4));
     }

     public int getPosition() {
       return position;
     }

     public int getLength() {
       return length;
     }

     public boolean isEmpty() {
       return this == EMPTY;
     }
   }

   public static AndroidApiDataAccess create(
       InternalOptions options, DiagnosticsHandler diagnosticsHandler) {
     URL resource = AndroidApiDataAccess.class.getClassLoader().getResource(RESOURCE_NAME);
     if (resource == null) {
       diagnosticsHandler.warning(
           new StringDiagnostic("Could not find the api database at " + RESOURCE_NAME));
       return new AndroidApiDataAccessNoBacking();
     }
     if (options.apiModelingOptions().useMemoryMappedByteBuffer) {
       try {
         // The resource is encoded as protocol and a path, where we should have one of either:
         // protocol: file, path: <path-to-file>
         // protocol: jar, path: file:<path-to-jar>!/<resource-name-in-jar>
         if (resource.getProtocol().equals("file")) {
           return getDataAccessFromPathAndOffset(Paths.get(resource.toURI()), 0);
         } else if (resource.getProtocol().equals("jar") && resource.getPath().startsWith("file:")) {
           // The path is on form 'file:<path-to-jar>!/<resource-name-in-jar>
           JarURLConnection jarUrl = (JarURLConnection) resource.openConnection();
           File jarFile = new File(jarUrl.getJarFileURL().getFile());
           String databaseEntry = jarUrl.getEntryName();
           long offsetInJar = getOffsetOfResourceInZip(jarFile, databaseEntry);
           if (offsetInJar > 0) {
             return getDataAccessFromPathAndOffset(jarFile.toPath(), offsetInJar);
           }
         }
         // On older DEX platforms creating a new byte channel may fail:
         // Error: java.lang.NoSuchMethodError: No static method newByteChannel(Ljava/nio/file/Path;
         // [Ljava/nio/file/OpenOption;)Ljava/nio/channels/SeekableByteChannel;
         // in class Ljava/nio/file/Files
       } catch (Exception | NoSuchMethodError e) {
         diagnosticsHandler.warning(new ExceptionDiagnostic(e));
       }
       diagnosticsHandler.warning(
           new StringDiagnostic(
               "Unable to use a memory mapped byte buffer to access the api database. Falling back"
                   + " to loading the database into program which requires more memory"));
     }
     try (InputStream apiInputStream =
         AndroidApiDataAccess.class.getClassLoader().getResourceAsStream(RESOURCE_NAME)) {
       if (apiInputStream == null) {
         diagnosticsHandler.warning(
             new StringDiagnostic("Could not open the api database at " + RESOURCE_NAME));
         return new AndroidApiDataAccessNoBacking();
       }
       return new AndroidApiDataAccessInMemory(ByteStreams.toByteArray(apiInputStream));
     } catch (IOException e) {
       diagnosticsHandler.warning(new ExceptionDiagnostic(e));
       return new AndroidApiDataAccessNoBacking();
     }
   }

   private static AndroidApiDataAccessByteMapped getDataAccessFromPathAndOffset(
       Path path, long offset) throws IOException {
     FileChannel fileChannel = (FileChannel) Files.newByteChannel(path, StandardOpenOption.READ);
     MappedByteBuffer mappedByteBuffer =
         fileChannel.map(FileChannel.MapMode.READ_ONLY, offset, fileChannel.size() - offset);
     // Ensure that we can run on JDK 8 by using the CompatByteBuffer.
     return new AndroidApiDataAccessByteMapped(new CompatByteBuffer(mappedByteBuffer));
   }

   public static int entrySizeInBitsForConstantPoolMap() {
     return ENTRY_SIZE_IN_BITS_FOR_CONSTANT_POOL_MAP;
   }

   public static int entrySizeInBitsForApiLevelMap() {
     return ENTRY_SIZE_IN_BITS_FOR_API_MAP;
   }

   public static int apiLevelHash(DexReference reference) {
     int entrySize = entrySizeInBitsForApiLevelMap();
     int size = 1 << (entrySize - 1);
     return (reference.hashCode() % size) + size;
   }

   public static int constantPoolHash(DexString string) {
     int entrySize = entrySizeInBitsForConstantPoolMap();
     int size = 1 << (entrySize - 1);
     return (string.hashCode() % size) + size;
   }

   static int constantPoolEntrySize() {
     return PAYLOAD_OFFSET_WITH_LENGTH;
   }

   static int constantPoolMapEntrySize() {
     return PAYLOAD_OFFSET_WITH_LENGTH;
   }

   static int apiLevelHashMapEntrySize() {
     return PAYLOAD_OFFSET_WITH_LENGTH;
   }

   /** The start of the constant pool */
   public static int constantPoolOffset() {
     return 4;
   }

   /** The start of the constant pool hash map. */
   public static int constantPoolHashMapOffset(int constantPoolSize) {
     return (constantPoolSize * constantPoolEntrySize()) + constantPoolOffset();
   }

   /** The start of the api level hash map. */
   public static int apiLevelHashMapOffset(int constantPoolSize) {
     int constantPoolHashMapSize =
         (1 << entrySizeInBitsForConstantPoolMap()) * constantPoolMapEntrySize();
     return constantPoolHashMapOffset(constantPoolSize) + constantPoolHashMapSize;
   }

   /** The start of the payload section. */
   public static int payloadOffset(int constantPoolSize) {
     int apiLevelSize = (1 << entrySizeInBitsForApiLevelMap()) * apiLevelHashMapEntrySize();
     return apiLevelHashMapOffset(constantPoolSize) + apiLevelSize;
   }

   /** The actual byte index of the constant pool index. */
   public int constantPoolIndexOffset(int index) {
     return constantPoolOffset() + (index * constantPoolEntrySize());
   }

   /** The actual byte index of the constant pool hash key. */
   protected int constantPoolHashMapIndexOffset(int hash) {
     return constantPoolHashMapOffset(getConstantPoolSize()) + (hash * constantPoolMapEntrySize());
   }

   /** The actual byte index of the api hash key. */
   protected int apiLevelHashMapIndexOffset(int hash) {
     return apiLevelHashMapOffset(getConstantPoolSize()) + (hash * apiLevelHashMapEntrySize());
   }

   static int readIntFromOffset(byte[] data, int offset) {
     return Ints.fromBytes(data[offset], data[offset + 1], data[offset + 2], data[offset + 3]);
   }

   static int readShortFromOffset(byte[] data, int offset) {
     return Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[offset], data[offset + 1]);
   }

   private int constantPoolSizeCache = -1;

   abstract int readConstantPoolSize();

   abstract PositionAndLength readPositionAndLength(int offset);

   abstract boolean payloadHasConstantPoolValue(int offset, int length, byte[] value);

   abstract int payloadContainsConstantPoolValue(
       int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate);

   abstract byte readApiLevelForPayloadOffset(int offset, int length, byte[] value);

   public int getConstantPoolSize() {
     if (constantPoolSizeCache == -1) {
       constantPoolSizeCache = readConstantPoolSize();
     }
     return constantPoolSizeCache;
   }

   /** When the first bit is set (position < 0) then there is a single unique result for the hash. */
   public static boolean isUniqueConstantPoolEntry(int position) {
     return position < 0;
   }

   /**
    * If the position defines a unique result, the first byte is has the first bit set to 1 (making
    * it negative) and the actual index specified in the least significant two bytes.
    */
   public static int getConstantPoolIndexFromUniqueConstantPoolEntry(int position) {
     assert isUniqueConstantPoolEntry(position);
     return unsetBitAtIndex(position, 32);
   }

   public int getConstantPoolIndex(DexString string) {
     PositionAndLength constantPoolIndex =
         readPositionAndLength(constantPoolHashMapIndexOffset(constantPoolHash(string)));
     if (constantPoolIndex.isEmpty()) {
       return -1;
     }
     int position = constantPoolIndex.getPosition();
     int length = constantPoolIndex.getLength();
     if (isUniqueConstantPoolEntry(position)) {
       int nonTaggedPosition = getConstantPoolIndexFromUniqueConstantPoolEntry(position);
       if (isConstantPoolEntry(nonTaggedPosition, string.content)) {
         return nonTaggedPosition;
       }
     } else {
       assert length > 0;
       return payloadContainsConstantPoolValue(
           payloadOffset(getConstantPoolSize()) + position,
           length,
           string.content,
           this::isConstantPoolEntry);
     }
     return -1;
   }

   public boolean isConstantPoolEntry(int index, byte[] value) {
     PositionAndLength constantPoolPayloadOffset =
         readPositionAndLength(constantPoolIndexOffset(index));
     if (constantPoolPayloadOffset.isEmpty()) {
       return false;
     }
     if (value.length != constantPoolPayloadOffset.getLength()) {
       return false;
     }
     return payloadHasConstantPoolValue(
         payloadOffset(getConstantPoolSize()) + constantPoolPayloadOffset.getPosition(),
         constantPoolPayloadOffset.getLength(),
         value);
   }

   public byte getApiLevelForReference(byte[] serialized, DexReference reference) {
     PositionAndLength apiLevelPayloadOffset =
         readPositionAndLength(apiLevelHashMapIndexOffset(apiLevelHash(reference)));
     if (apiLevelPayloadOffset.isEmpty()) {
       return 0;
     }
     return readApiLevelForPayloadOffset(
         payloadOffset(getConstantPoolSize()) + apiLevelPayloadOffset.getPosition(),
         apiLevelPayloadOffset.getLength(),
         serialized);
   }

   public boolean isNoBacking() {
     return false;
   }

   public static class AndroidApiDataAccessByteMapped extends AndroidApiDataAccess {

     private final CompatByteBuffer mappedByteBuffer;

     public AndroidApiDataAccessByteMapped(CompatByteBuffer mappedByteBuffer) {
       this.mappedByteBuffer = mappedByteBuffer;
     }

     @Override
     int readConstantPoolSize() {
       return mappedByteBuffer.getInt(0);
     }

     @Override
     public PositionAndLength readPositionAndLength(int offset) {
       return PositionAndLength.create(
           mappedByteBuffer.getInt(offset), mappedByteBuffer.getShort(offset + 4));
     }

     @Override
     boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
       assert length == value.length;
       mappedByteBuffer.position(offset);
       for (byte expected : value) {
         if (expected != mappedByteBuffer.get()) {
           return false;
         }
       }
       return true;
     }

     @Override
     int payloadContainsConstantPoolValue(
         int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
       for (int i = offset; i < offset + length; i += 2) {
         // Do not use mappedByteBuffer.getShort() since that will add the sign.
         int index =
             Ints.fromBytes(
                 ZERO_BYTE, ZERO_BYTE, mappedByteBuffer.get(i), mappedByteBuffer.get(i + 1));
         if (predicate.test(index, value)) {
           return index;
         }
       }
       return -1;
     }

     @Override
     byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
       int currentOffset = offset;
       while (currentOffset < offset + length) {
         // Read the length
         int lengthOfEntry =
             Ints.fromBytes(
                 ZERO_BYTE,
                 ZERO_BYTE,
                 mappedByteBuffer.get(currentOffset),
                 mappedByteBuffer.get(currentOffset + 1));
         int startPosition = currentOffset + 2;
         if (value.length == lengthOfEntry
             && payloadHasConstantPoolValue(startPosition, lengthOfEntry, value)) {
           return mappedByteBuffer.get(startPosition + lengthOfEntry);
         }
         // Advance our current position + length of entry + api level.
         currentOffset = startPosition + lengthOfEntry + 1;
       }
       return -1;
     }
   }

   public static class AndroidApiDataAccessInMemory extends AndroidApiDataAccess {

     private final byte[] data;

     private AndroidApiDataAccessInMemory(byte[] data) {
       this.data = data;
     }

     @Override
     public int readConstantPoolSize() {
       return readIntFromOffset(data, 0);
     }

     @Override
     PositionAndLength readPositionAndLength(int offset) {
       return PositionAndLength.create(data, offset);
     }

     @Override
     boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
       if (value.length != length) {
         return false;
       }
       for (int i = 0; i < length; i++) {
         if (value[i] != data[i + offset]) {
           return false;
         }
       }
       return true;
     }

     @Override
     int payloadContainsConstantPoolValue(
         int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
       if (data.length < length) {
         return -1;
       }
       for (int i = offset; i < offset + length; i += 2) {
         int index = Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[i], data[i + 1]);
         if (predicate.test(index, value)) {
           return index;
         }
       }
       return -1;
     }

     @Override
     byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
       int index = offset;
       while (index < offset + length) {
         // Read size of entry
         int lengthOfEntry = Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[index], data[index + 1]);
         int startIndex = index + 2;
         int endIndex = startIndex + lengthOfEntry;
         if (payloadHasConstantPoolValue(startIndex, lengthOfEntry, value)) {
           return data[endIndex];
         }
         index = endIndex + 1;
       }
       return 0;
     }
   }

   public static class AndroidApiDataAccessNoBacking extends AndroidApiDataAccess {

     @Override
     int readConstantPoolSize() {
       throw new Unreachable();
     }

     @Override
     PositionAndLength readPositionAndLength(int offset) {
       throw new Unreachable();
     }

     @Override
     boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
       throw new Unreachable();
     }

     @Override
     int payloadContainsConstantPoolValue(
         int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
       throw new Unreachable();
     }

     @Override
     byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
       throw new Unreachable();
     }

     @Override
     public boolean isNoBacking() {
       return true;
     }
   }
 }
	// Copyright (c) 2022, the R8 project authors. Please see the AUTHORS file
	// for details. All rights reserved. Use of this source code is governed by a
	// BSD-style license that can be found in the LICENSE file.

	package com.android.tools.r8.androidapi;

	import static com.android.tools.r8.lightir.ByteUtils.unsetBitAtIndex;
	import static com.android.tools.r8.utils.ZipUtils.getOffsetOfResourceInZip;

	import com.android.tools.r8.DiagnosticsHandler;
	import com.android.tools.r8.dex.CompatByteBuffer;
	import com.android.tools.r8.errors.Unreachable;
	import com.android.tools.r8.graph.DexReference;
	import com.android.tools.r8.graph.DexString;
	import com.android.tools.r8.utils.ExceptionDiagnostic;
	import com.android.tools.r8.utils.InternalOptions;
	import com.android.tools.r8.utils.StringDiagnostic;
	import com.google.common.io.ByteStreams;
	import com.google.common.primitives.Ints;
	import java.io.File;
	import java.io.IOException;
	import java.io.InputStream;
	import java.net.JarURLConnection;
	import java.net.URL;
	import java.nio.MappedByteBuffer;
	import java.nio.channels.FileChannel;
	import java.nio.file.Files;
	import java.nio.file.Path;
	import java.nio.file.Paths;
	import java.nio.file.StandardOpenOption;
	import java.util.function.BiPredicate;

	/**
	* Implements low-level access methods for seeking on top of the database file defined by {@code
	* AndroidApiLevelHashingDatabaseImpl} where a description of the format can also be found.
	*/
	public abstract class AndroidApiDataAccess {

	private static final String RESOURCE_NAME = "resources/new_api_database.ser";
	private static final int ENTRY_SIZE_IN_BITS_FOR_CONSTANT_POOL_MAP = 17;
	private static final int ENTRY_SIZE_IN_BITS_FOR_API_MAP = 18;
	// The payload offset is an offset into the payload defined by an integer and a length defined by
	// a short.
	private static final int PAYLOAD_OFFSET_WITH_LENGTH = 4 + 2;
	private static final byte ZERO_BYTE = (byte) 0;

	public static boolean isApiDatabaseEntry(String entry) {
	return RESOURCE_NAME.equals(entry);
	}

	private static class PositionAndLength {

	private static final PositionAndLength EMPTY = new PositionAndLength(0, 0);

	private final int position;
	private final int length;

	private PositionAndLength(int position, int length) {
	this.position = position;
	this.length = length;
	}

	public static PositionAndLength create(int position, int length) {
	if (position == 0 && length == 0) {
	return EMPTY;
	}
	if ((position < 0 && length > 0) \|\| (position > 0 && length == 0)) {
	assert false : "Unexpected position and length";
	return EMPTY;
	}
	return new PositionAndLength(position, length);
	}

	public static PositionAndLength create(byte[] data, int offset) {
	return create(readIntFromOffset(data, offset), readShortFromOffset(data, offset + 4));
	}

	public int getPosition() {
	return position;
	}

	public int getLength() {
	return length;
	}

	public boolean isEmpty() {
	return this == EMPTY;
	}
	}

	public static AndroidApiDataAccess create(
	InternalOptions options, DiagnosticsHandler diagnosticsHandler) {
	URL resource = AndroidApiDataAccess.class.getClassLoader().getResource(RESOURCE_NAME);
	if (resource == null) {
	diagnosticsHandler.warning(
	new StringDiagnostic("Could not find the api database at " + RESOURCE_NAME));
	return new AndroidApiDataAccessNoBacking();
	}
	if (options.apiModelingOptions().useMemoryMappedByteBuffer) {
	try {
	// The resource is encoded as protocol and a path, where we should have one of either:
	// protocol: file, path: <path-to-file>
	// protocol: jar, path: file:<path-to-jar>!/<resource-name-in-jar>
	if (resource.getProtocol().equals("file")) {
	return getDataAccessFromPathAndOffset(Paths.get(resource.toURI()), 0);
	} else if (resource.getProtocol().equals("jar") && resource.getPath().startsWith("file:")) {
	// The path is on form 'file:<path-to-jar>!/<resource-name-in-jar>
	JarURLConnection jarUrl = (JarURLConnection) resource.openConnection();
	File jarFile = new File(jarUrl.getJarFileURL().getFile());
	String databaseEntry = jarUrl.getEntryName();
	long offsetInJar = getOffsetOfResourceInZip(jarFile, databaseEntry);
	if (offsetInJar > 0) {
	return getDataAccessFromPathAndOffset(jarFile.toPath(), offsetInJar);
	}
	}
	// On older DEX platforms creating a new byte channel may fail:
	// Error: java.lang.NoSuchMethodError: No static method newByteChannel(Ljava/nio/file/Path;
	// [Ljava/nio/file/OpenOption;)Ljava/nio/channels/SeekableByteChannel;
	// in class Ljava/nio/file/Files
	} catch (Exception \| NoSuchMethodError e) {
	diagnosticsHandler.warning(new ExceptionDiagnostic(e));
	}
	diagnosticsHandler.warning(
	new StringDiagnostic(
	"Unable to use a memory mapped byte buffer to access the api database. Falling back"
	+ " to loading the database into program which requires more memory"));
	}
	try (InputStream apiInputStream =
	AndroidApiDataAccess.class.getClassLoader().getResourceAsStream(RESOURCE_NAME)) {
	if (apiInputStream == null) {
	diagnosticsHandler.warning(
	new StringDiagnostic("Could not open the api database at " + RESOURCE_NAME));
	return new AndroidApiDataAccessNoBacking();
	}
	return new AndroidApiDataAccessInMemory(ByteStreams.toByteArray(apiInputStream));
	} catch (IOException e) {
	diagnosticsHandler.warning(new ExceptionDiagnostic(e));
	return new AndroidApiDataAccessNoBacking();
	}
	}

	private static AndroidApiDataAccessByteMapped getDataAccessFromPathAndOffset(
	Path path, long offset) throws IOException {
	FileChannel fileChannel = (FileChannel) Files.newByteChannel(path, StandardOpenOption.READ);
	MappedByteBuffer mappedByteBuffer =
	fileChannel.map(FileChannel.MapMode.READ_ONLY, offset, fileChannel.size() - offset);
	// Ensure that we can run on JDK 8 by using the CompatByteBuffer.
	return new AndroidApiDataAccessByteMapped(new CompatByteBuffer(mappedByteBuffer));
	}

	public static int entrySizeInBitsForConstantPoolMap() {
	return ENTRY_SIZE_IN_BITS_FOR_CONSTANT_POOL_MAP;
	}

	public static int entrySizeInBitsForApiLevelMap() {
	return ENTRY_SIZE_IN_BITS_FOR_API_MAP;
	}

	public static int apiLevelHash(DexReference reference) {
	int entrySize = entrySizeInBitsForApiLevelMap();
	int size = 1 << (entrySize - 1);
	return (reference.hashCode() % size) + size;
	}

	public static int constantPoolHash(DexString string) {
	int entrySize = entrySizeInBitsForConstantPoolMap();
	int size = 1 << (entrySize - 1);
	return (string.hashCode() % size) + size;
	}

	static int constantPoolEntrySize() {
	return PAYLOAD_OFFSET_WITH_LENGTH;
	}

	static int constantPoolMapEntrySize() {
	return PAYLOAD_OFFSET_WITH_LENGTH;
	}

	static int apiLevelHashMapEntrySize() {
	return PAYLOAD_OFFSET_WITH_LENGTH;
	}

	/** The start of the constant pool */
	public static int constantPoolOffset() {
	return 4;
	}

	/** The start of the constant pool hash map. */
	public static int constantPoolHashMapOffset(int constantPoolSize) {
	return (constantPoolSize * constantPoolEntrySize()) + constantPoolOffset();
	}

	/** The start of the api level hash map. */
	public static int apiLevelHashMapOffset(int constantPoolSize) {
	int constantPoolHashMapSize =
	(1 << entrySizeInBitsForConstantPoolMap()) * constantPoolMapEntrySize();
	return constantPoolHashMapOffset(constantPoolSize) + constantPoolHashMapSize;
	}

	/** The start of the payload section. */
	public static int payloadOffset(int constantPoolSize) {
	int apiLevelSize = (1 << entrySizeInBitsForApiLevelMap()) * apiLevelHashMapEntrySize();
	return apiLevelHashMapOffset(constantPoolSize) + apiLevelSize;
	}

	/** The actual byte index of the constant pool index. */
	public int constantPoolIndexOffset(int index) {
	return constantPoolOffset() + (index * constantPoolEntrySize());
	}

	/** The actual byte index of the constant pool hash key. */
	protected int constantPoolHashMapIndexOffset(int hash) {
	return constantPoolHashMapOffset(getConstantPoolSize()) + (hash * constantPoolMapEntrySize());
	}

	/** The actual byte index of the api hash key. */
	protected int apiLevelHashMapIndexOffset(int hash) {
	return apiLevelHashMapOffset(getConstantPoolSize()) + (hash * apiLevelHashMapEntrySize());
	}

	static int readIntFromOffset(byte[] data, int offset) {
	return Ints.fromBytes(data[offset], data[offset + 1], data[offset + 2], data[offset + 3]);
	}

	static int readShortFromOffset(byte[] data, int offset) {
	return Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[offset], data[offset + 1]);
	}

	private int constantPoolSizeCache = -1;

	abstract int readConstantPoolSize();

	abstract PositionAndLength readPositionAndLength(int offset);

	abstract boolean payloadHasConstantPoolValue(int offset, int length, byte[] value);

	abstract int payloadContainsConstantPoolValue(
	int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate);

	abstract byte readApiLevelForPayloadOffset(int offset, int length, byte[] value);

	public int getConstantPoolSize() {
	if (constantPoolSizeCache == -1) {
	constantPoolSizeCache = readConstantPoolSize();
	}
	return constantPoolSizeCache;
	}

	/** When the first bit is set (position < 0) then there is a single unique result for the hash. */
	public static boolean isUniqueConstantPoolEntry(int position) {
	return position < 0;
	}

	/**
	* If the position defines a unique result, the first byte is has the first bit set to 1 (making
	* it negative) and the actual index specified in the least significant two bytes.
	*/
	public static int getConstantPoolIndexFromUniqueConstantPoolEntry(int position) {
	assert isUniqueConstantPoolEntry(position);
	return unsetBitAtIndex(position, 32);
	}

	public int getConstantPoolIndex(DexString string) {
	PositionAndLength constantPoolIndex =
	readPositionAndLength(constantPoolHashMapIndexOffset(constantPoolHash(string)));
	if (constantPoolIndex.isEmpty()) {
	return -1;
	}
	int position = constantPoolIndex.getPosition();
	int length = constantPoolIndex.getLength();
	if (isUniqueConstantPoolEntry(position)) {
	int nonTaggedPosition = getConstantPoolIndexFromUniqueConstantPoolEntry(position);
	if (isConstantPoolEntry(nonTaggedPosition, string.content)) {
	return nonTaggedPosition;
	}
	} else {
	assert length > 0;
	return payloadContainsConstantPoolValue(
	payloadOffset(getConstantPoolSize()) + position,
	length,
	string.content,
	this::isConstantPoolEntry);
	}
	return -1;
	}

	public boolean isConstantPoolEntry(int index, byte[] value) {
	PositionAndLength constantPoolPayloadOffset =
	readPositionAndLength(constantPoolIndexOffset(index));
	if (constantPoolPayloadOffset.isEmpty()) {
	return false;
	}
	if (value.length != constantPoolPayloadOffset.getLength()) {
	return false;
	}
	return payloadHasConstantPoolValue(
	payloadOffset(getConstantPoolSize()) + constantPoolPayloadOffset.getPosition(),
	constantPoolPayloadOffset.getLength(),
	value);
	}

	public byte getApiLevelForReference(byte[] serialized, DexReference reference) {
	PositionAndLength apiLevelPayloadOffset =
	readPositionAndLength(apiLevelHashMapIndexOffset(apiLevelHash(reference)));
	if (apiLevelPayloadOffset.isEmpty()) {
	return 0;
	}
	return readApiLevelForPayloadOffset(
	payloadOffset(getConstantPoolSize()) + apiLevelPayloadOffset.getPosition(),
	apiLevelPayloadOffset.getLength(),
	serialized);
	}

	public boolean isNoBacking() {
	return false;
	}

	public static class AndroidApiDataAccessByteMapped extends AndroidApiDataAccess {

	private final CompatByteBuffer mappedByteBuffer;

	public AndroidApiDataAccessByteMapped(CompatByteBuffer mappedByteBuffer) {
	this.mappedByteBuffer = mappedByteBuffer;
	}

	@Override
	int readConstantPoolSize() {
	return mappedByteBuffer.getInt(0);
	}

	@Override
	public PositionAndLength readPositionAndLength(int offset) {
	return PositionAndLength.create(
	mappedByteBuffer.getInt(offset), mappedByteBuffer.getShort(offset + 4));
	}

	@Override
	boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
	assert length == value.length;
	mappedByteBuffer.position(offset);
	for (byte expected : value) {
	if (expected != mappedByteBuffer.get()) {
	return false;
	}
	}
	return true;
	}

	@Override
	int payloadContainsConstantPoolValue(
	int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
	for (int i = offset; i < offset + length; i += 2) {
	// Do not use mappedByteBuffer.getShort() since that will add the sign.
	int index =
	Ints.fromBytes(
	ZERO_BYTE, ZERO_BYTE, mappedByteBuffer.get(i), mappedByteBuffer.get(i + 1));
	if (predicate.test(index, value)) {
	return index;
	}
	}
	return -1;
	}

	@Override
	byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
	int currentOffset = offset;
	while (currentOffset < offset + length) {
	// Read the length
	int lengthOfEntry =
	Ints.fromBytes(
	ZERO_BYTE,
	ZERO_BYTE,
	mappedByteBuffer.get(currentOffset),
	mappedByteBuffer.get(currentOffset + 1));
	int startPosition = currentOffset + 2;
	if (value.length == lengthOfEntry
	&& payloadHasConstantPoolValue(startPosition, lengthOfEntry, value)) {
	return mappedByteBuffer.get(startPosition + lengthOfEntry);
	}
	// Advance our current position + length of entry + api level.
	currentOffset = startPosition + lengthOfEntry + 1;
	}
	return -1;
	}
	}

	public static class AndroidApiDataAccessInMemory extends AndroidApiDataAccess {

	private final byte[] data;

	private AndroidApiDataAccessInMemory(byte[] data) {
	this.data = data;
	}

	@Override
	public int readConstantPoolSize() {
	return readIntFromOffset(data, 0);
	}

	@Override
	PositionAndLength readPositionAndLength(int offset) {
	return PositionAndLength.create(data, offset);
	}

	@Override
	boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
	if (value.length != length) {
	return false;
	}
	for (int i = 0; i < length; i++) {
	if (value[i] != data[i + offset]) {
	return false;
	}
	}
	return true;
	}

	@Override
	int payloadContainsConstantPoolValue(
	int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
	if (data.length < length) {
	return -1;
	}
	for (int i = offset; i < offset + length; i += 2) {
	int index = Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[i], data[i + 1]);
	if (predicate.test(index, value)) {
	return index;
	}
	}
	return -1;
	}

	@Override
	byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
	int index = offset;
	while (index < offset + length) {
	// Read size of entry
	int lengthOfEntry = Ints.fromBytes(ZERO_BYTE, ZERO_BYTE, data[index], data[index + 1]);
	int startIndex = index + 2;
	int endIndex = startIndex + lengthOfEntry;
	if (payloadHasConstantPoolValue(startIndex, lengthOfEntry, value)) {
	return data[endIndex];
	}
	index = endIndex + 1;
	}
	return 0;
	}
	}

	public static class AndroidApiDataAccessNoBacking extends AndroidApiDataAccess {

	@Override
	int readConstantPoolSize() {
	throw new Unreachable();
	}

	@Override
	PositionAndLength readPositionAndLength(int offset) {
	throw new Unreachable();
	}

	@Override
	boolean payloadHasConstantPoolValue(int offset, int length, byte[] value) {
	throw new Unreachable();
	}

	@Override
	int payloadContainsConstantPoolValue(
	int offset, int length, byte[] value, BiPredicate<Integer, byte[]> predicate) {
	throw new Unreachable();
	}

	@Override
	byte readApiLevelForPayloadOffset(int offset, int length, byte[] value) {
	throw new Unreachable();
	}

	@Override
	public boolean isNoBacking() {
	return true;
	}
	}
	}