Add Ver4DictDecoder.

Bug: 9618601
Change-Id: I43c5840505c6a847aaf4893a400392ccd45903c0

8 files changed, 482 insertions, 193 deletions

diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
index 5b319ad90..665c7a27c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
@@ -498,7 +498,7 @@ public final class BinaryDictDecoderUtils {
 
             // reach the end of the array.
             if (options.mSupportsDynamicUpdate) {
-                final boolean hasValidForwardLink = dictDecoder.readForwardLinkAndAdvancePosition();
+                final boolean hasValidForwardLink = dictDecoder.readAndFollowForwardLink();
                 if (!hasValidForwardLink) break;
             }
         } while (options.mSupportsDynamicUpdate && dictDecoder.hasNextPtNodeArray());
@@ -550,7 +550,7 @@ public final class BinaryDictDecoderUtils {
      * @return the created (or merged) dictionary.
      */
     @UsedForTesting
-    /* package */ static FusionDictionary readDictionaryBinary(final Ver3DictDecoder dictDecoder,
+    /* package */ static FusionDictionary readDictionaryBinary(final DictDecoder dictDecoder,
             final FusionDictionary dict) throws IOException, UnsupportedFormatException {
         // Read header
         final FileHeader fileHeader = dictDecoder.readHeader();
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
index 70931f885..4dba8e5cf 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
@@ -368,9 +368,9 @@ public class BinaryDictEncoderUtils {
             if (null != ptNode.mBigrams) {
                 for (WeightedString bigram : ptNode.mBigrams) {
                     final int offset = getOffsetToTargetPtNodeDuringUpdate(ptNodeArray,
-                            nodeSize + size + FormatSpec.PTNODE_FLAGS_SIZE,
+                            nodeSize + size + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE,
                             FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord));
-                    nodeSize += getByteSize(offset) + FormatSpec.PTNODE_FLAGS_SIZE;
+                    nodeSize += getByteSize(offset) + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE;
                 }
             }
             ptNode.mCachedSize = nodeSize;
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
index 2c5e93e5c..a282f595c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
@@ -114,7 +114,7 @@ public final class BinaryDictIOUtils {
             if (p.mPosition == p.mNumOfPtNode) {
                 if (formatOptions.mSupportsDynamicUpdate) {
                     final boolean hasValidForwardLinkAddress =
-                            dictDecoder.readForwardLinkAndAdvancePosition();
+                            dictDecoder.readAndFollowForwardLink();
                     if (hasValidForwardLinkAddress && dictDecoder.hasNextPtNodeArray()) {
                         // The node array has a forward link.
                         p.mNumOfPtNode = Position.NOT_READ_PTNODE_COUNT;
@@ -233,7 +233,7 @@ public final class BinaryDictIOUtils {
                 }
 
                 final boolean hasValidForwardLinkAddress =
-                        dictDecoder.readForwardLinkAndAdvancePosition();
+                        dictDecoder.readAndFollowForwardLink();
                 if (!hasValidForwardLinkAddress || !dictDecoder.hasNextPtNodeArray()) {
                     return FormatSpec.NOT_VALID_WORD;
                 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
index 40e852423..3796a466c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DictDecoder.java
@@ -17,9 +17,11 @@
 package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.CharEncoding;
 import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.DictBuffer;
 import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
 import com.android.inputmethod.latin.utils.ByteArrayDictBuffer;
 
 import java.io.File;
@@ -30,13 +32,50 @@ import java.io.RandomAccessFile;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.TreeMap;
 
 /**
- * An interface of binary dictionary decoder.
+ * The base class of binary dictionary decoders.
  */
-public interface DictDecoder {
-    public FileHeader readHeader() throws IOException, UnsupportedFormatException;
+public abstract class DictDecoder {
+
+    protected FileHeader readHeader(final DictBuffer dictBuffer)
+            throws IOException, UnsupportedFormatException {
+        if (dictBuffer == null) {
+            openDictBuffer();
+        }
+
+        final int version = HeaderReader.readVersion(dictBuffer);
+        if (version < FormatSpec.MINIMUM_SUPPORTED_VERSION
+                || version > FormatSpec.MAXIMUM_SUPPORTED_VERSION) {
+            throw new UnsupportedFormatException("Unsupported version : " + version);
+        }
+        // TODO: Remove this field.
+        final int optionsFlags = HeaderReader.readOptionFlags(dictBuffer);
+
+        final int headerSize = HeaderReader.readHeaderSize(dictBuffer);
+
+        if (headerSize < 0) {
+            throw new UnsupportedFormatException("header size can't be negative.");
+        }
+
+        final HashMap<String, String> attributes = HeaderReader.readAttributes(dictBuffer,
+                headerSize);
+
+        final FileHeader header = new FileHeader(headerSize,
+                new FusionDictionary.DictionaryOptions(attributes,
+                        0 != (optionsFlags & FormatSpec.GERMAN_UMLAUT_PROCESSING_FLAG),
+                        0 != (optionsFlags & FormatSpec.FRENCH_LIGATURE_PROCESSING_FLAG)),
+                        new FormatOptions(version,
+                                0 != (optionsFlags & FormatSpec.SUPPORTS_DYNAMIC_UPDATE)));
+        return header;
+    }
+
+    /**
+     * Reads and returns the file header.
+     */
+    public abstract FileHeader readHeader() throws IOException, UnsupportedFormatException;
 
     /**
      * Reads PtNode from nodeAddress.
@@ -44,7 +83,7 @@ public interface DictDecoder {
      * @param formatOptions the format options.
      * @return PtNodeInfo.
      */
-    public PtNodeInfo readPtNode(final int ptNodePos, final FormatOptions formatOptions);
+    public abstract PtNodeInfo readPtNode(final int ptNodePos, final FormatOptions formatOptions);
 
     /**
      * Reads a buffer and returns the memory representation of the dictionary.
@@ -59,9 +98,9 @@ public interface DictDecoder {
      * @return the created (or merged) dictionary.
      */
     @UsedForTesting
-    public FusionDictionary readDictionaryBinary(final FusionDictionary dict,
+    public abstract FusionDictionary readDictionaryBinary(final FusionDictionary dict,
             final boolean deleteDictIfBroken)
-            throws FileNotFoundException, IOException, UnsupportedFormatException;
+                    throws FileNotFoundException, IOException, UnsupportedFormatException;
 
     /**
      * Gets the address of the last PtNode of the exact matching word in the dictionary.
@@ -74,7 +113,12 @@ public interface DictDecoder {
      */
     @UsedForTesting
     public int getTerminalPosition(final String word)
-            throws IOException, UnsupportedFormatException;
+            throws IOException, UnsupportedFormatException {
+        if (!isDictBufferOpen()) {
+            openDictBuffer();
+        }
+        return BinaryDictIOUtils.getTerminalPosition(this, word);
+    }
 
     /**
      * Reads unigrams and bigrams from the binary file.
@@ -86,50 +130,56 @@ public interface DictDecoder {
      * @throws IOException if the file can't be read.
      * @throws UnsupportedFormatException if the format of the file is not recognized.
      */
+    @UsedForTesting
     public void readUnigramsAndBigramsBinary(final TreeMap<Integer, String> words,
             final TreeMap<Integer, Integer> frequencies,
             final TreeMap<Integer, ArrayList<PendingAttribute>> bigrams)
-            throws IOException, UnsupportedFormatException;
+            throws IOException, UnsupportedFormatException {
+        if (!isDictBufferOpen()) {
+            openDictBuffer();
+        }
+        BinaryDictIOUtils.readUnigramsAndBigramsBinary(this, words, frequencies, bigrams);
+    }
 
     /**
      * Sets the position of the buffer to the given value.
      *
      * @param newPos the new position
      */
-    public void setPosition(final int newPos);
+    public abstract void setPosition(final int newPos);
 
     /**
      * Gets the position of the buffer.
      *
      * @return the position
      */
-    public int getPosition();
+    public abstract int getPosition();
 
     /**
      * Reads and returns the PtNode count out of a buffer and forwards the pointer.
      */
-    public int readPtNodeCount();
+    public abstract int readPtNodeCount();
 
     /**
      * Reads the forward link and advances the position.
      *
-     * @return if this method advances the position then true else false.
+     * @return true if this method moves the file pointer, false otherwise.
      */
-    public boolean readForwardLinkAndAdvancePosition();
-    public boolean hasNextPtNodeArray();
+    public abstract boolean readAndFollowForwardLink();
+    public abstract boolean hasNextPtNodeArray();
 
     /**
      * Opens the dictionary file and makes DictBuffer.
      */
     @UsedForTesting
-    public void openDictBuffer() throws FileNotFoundException, IOException;
+    public abstract void openDictBuffer() throws FileNotFoundException, IOException;
     @UsedForTesting
-    public boolean isOpenedDictBuffer();
+    public abstract boolean isDictBufferOpen();
 
-    // Flags for DictionaryBufferFactory.
+    // Constants for DictionaryBufferFactory.
     public static final int USE_READONLY_BYTEBUFFER = 0x01000000;
     public static final int USE_BYTEARRAY = 0x02000000;
-    public static final int USE_WRITABLE_BYTEBUFFER = 0x04000000;
+    public static final int USE_WRITABLE_BYTEBUFFER = 0x03000000;
     public static final int MASK_DICTBUFFER = 0x0F000000;
 
     public interface DictionaryBufferFactory {
@@ -221,4 +271,124 @@ public interface DictDecoder {
             return null;
         }
     }
+
+    /**
+     * A utility class for reading a file header.
+     */
+    protected static class HeaderReader {
+        protected static int readVersion(final DictBuffer dictBuffer)
+                throws IOException, UnsupportedFormatException {
+            return BinaryDictDecoderUtils.checkFormatVersion(dictBuffer);
+        }
+
+        protected static int readOptionFlags(final DictBuffer dictBuffer) {
+            return dictBuffer.readUnsignedShort();
+        }
+
+        protected static int readHeaderSize(final DictBuffer dictBuffer) {
+            return dictBuffer.readInt();
+        }
+
+        protected static HashMap<String, String> readAttributes(final DictBuffer dictBuffer,
+                final int headerSize) {
+            final HashMap<String, String> attributes = new HashMap<String, String>();
+            while (dictBuffer.position() < headerSize) {
+                // We can avoid an infinite loop here since dictBuffer.position() is always
+                // increased by calling CharEncoding.readString.
+                final String key = CharEncoding.readString(dictBuffer);
+                final String value = CharEncoding.readString(dictBuffer);
+                attributes.put(key, value);
+            }
+            dictBuffer.position(headerSize);
+            return attributes;
+        }
+    }
+
+    /**
+     * A utility class for reading a PtNode.
+     */
+    protected static class PtNodeReader {
+        protected static int readPtNodeOptionFlags(final DictBuffer dictBuffer) {
+            return dictBuffer.readUnsignedByte();
+        }
+
+        protected static int readParentAddress(final DictBuffer dictBuffer,
+                final FormatOptions formatOptions) {
+            if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
+                return BinaryDictDecoderUtils.readSInt24(dictBuffer);
+            } else {
+                return FormatSpec.NO_PARENT_ADDRESS;
+            }
+        }
+
+        protected static int readChildrenAddress(final DictBuffer dictBuffer, final int optionFlags,
+                final FormatOptions formatOptions) {
+            if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
+                final int address = BinaryDictDecoderUtils.readSInt24(dictBuffer);
+                if (address == 0) return FormatSpec.NO_CHILDREN_ADDRESS;
+                return address;
+            } else {
+                switch (optionFlags & FormatSpec.MASK_CHILDREN_ADDRESS_TYPE) {
+                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_ONEBYTE:
+                        return dictBuffer.readUnsignedByte();
+                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_TWOBYTES:
+                        return dictBuffer.readUnsignedShort();
+                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_THREEBYTES:
+                        return dictBuffer.readUnsignedInt24();
+                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_NOADDRESS:
+                    default:
+                        return FormatSpec.NO_CHILDREN_ADDRESS;
+                }
+            }
+        }
+
+        // Reads shortcuts and returns the read length.
+        protected static int readShortcut(final DictBuffer dictBuffer,
+                final ArrayList<WeightedString> shortcutTargets) {
+            final int pointerBefore = dictBuffer.position();
+            dictBuffer.readUnsignedShort(); // skip the size
+            while (true) {
+                final int targetFlags = dictBuffer.readUnsignedByte();
+                final String word = CharEncoding.readString(dictBuffer);
+                shortcutTargets.add(new WeightedString(word,
+                        targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY));
+                if (0 == (targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
+            }
+            return dictBuffer.position() - pointerBefore;
+        }
+
+        protected static int readBigramAddresses(final DictBuffer dictBuffer,
+                final ArrayList<PendingAttribute> bigrams, final int baseAddress) {
+            int readLength = 0;
+            int bigramCount = 0;
+            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
+                final int bigramFlags = dictBuffer.readUnsignedByte();
+                ++readLength;
+                final int sign = 0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_ATTR_OFFSET_NEGATIVE)
+                        ? 1 : -1;
+                int bigramAddress = baseAddress + readLength;
+                switch (bigramFlags & FormatSpec.MASK_BIGRAM_ATTR_ADDRESS_TYPE) {
+                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_ONEBYTE:
+                        bigramAddress += sign * dictBuffer.readUnsignedByte();
+                        readLength += 1;
+                        break;
+                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_TWOBYTES:
+                        bigramAddress += sign * dictBuffer.readUnsignedShort();
+                        readLength += 2;
+                        break;
+                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_THREEBYTES:
+                        bigramAddress += sign * dictBuffer.readUnsignedInt24();
+                        readLength += 3;
+                        break;
+                    default:
+                        throw new RuntimeException("Has bigrams with no address");
+                }
+                bigrams.add(new PendingAttribute(
+                        bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY,
+                        bigramAddress));
+                if (0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
+            }
+            return readLength;
+        }
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
index 96ccd8e49..51b89a02a 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FormatSpec.java
@@ -360,18 +360,26 @@ public final class FormatSpec {
      * Returns new dictionary decoder.
      *
      * @param dictFile the dictionary file.
-     * @param bufferType the flag indicating buffer type which is used by the dictionary decoder.
+     * @param bufferType The type of buffer, as one of USE_* in DictDecoder.
      * @return new dictionary decoder if the dictionary file exists, otherwise null.
      */
     public static DictDecoder getDictDecoder(final File dictFile, final int bufferType) {
-        if (!dictFile.isFile()) return null;
-        return new Ver3DictDecoder(dictFile, bufferType);
+        if (dictFile.isDirectory()) {
+            return new Ver4DictDecoder(dictFile, bufferType);
+        } else if (dictFile.isFile()) {
+            return new Ver3DictDecoder(dictFile, bufferType);
+        }
+        return null;
     }
 
     public static DictDecoder getDictDecoder(final File dictFile,
             final DictionaryBufferFactory factory) {
-        if (!dictFile.isFile()) return null;
-        return new Ver3DictDecoder(dictFile, factory);
+        if (dictFile.isDirectory()) {
+            return new Ver4DictDecoder(dictFile, factory);
+        } else if (dictFile.isFile()) {
+            return new Ver3DictDecoder(dictFile, factory);
+        }
+        return null;
     }
 
     public static DictDecoder getDictDecoder(final File dictFile) {
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver3DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver3DictDecoder.java
index 1a90a4b98..848277cd4 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver3DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver3DictDecoder.java
@@ -32,14 +32,12 @@ import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
-import java.util.TreeMap;
 
 /**
  * An implementation of DictDecoder for version 3 binary dictionary.
  */
 @UsedForTesting
-public class Ver3DictDecoder implements DictDecoder {
+public class Ver3DictDecoder extends DictDecoder {
     private static final String TAG = Ver3DictDecoder.class.getSimpleName();
 
     static {
@@ -49,124 +47,10 @@ public class Ver3DictDecoder implements DictDecoder {
     // TODO: implement something sensical instead of just a phony method
     private static native int doNothing();
 
-    private final static class HeaderReader {
-        protected static int readVersion(final DictBuffer dictBuffer)
-                throws IOException, UnsupportedFormatException {
-            return BinaryDictDecoderUtils.checkFormatVersion(dictBuffer);
-        }
-
-        protected static int readOptionFlags(final DictBuffer dictBuffer) {
-            return dictBuffer.readUnsignedShort();
-        }
-
-        protected static int readHeaderSize(final DictBuffer dictBuffer) {
-            return dictBuffer.readInt();
-        }
-
-        protected static HashMap<String, String> readAttributes(final DictBuffer dictBuffer,
-                final int headerSize) {
-            final HashMap<String, String> attributes = new HashMap<String, String>();
-            while (dictBuffer.position() < headerSize) {
-                // We can avoid an infinite loop here since dictBuffer.position() is always
-                // increased by calling CharEncoding.readString.
-                final String key = CharEncoding.readString(dictBuffer);
-                final String value = CharEncoding.readString(dictBuffer);
-                attributes.put(key, value);
-            }
-            dictBuffer.position(headerSize);
-            return attributes;
-        }
-    }
-
-    private final static class PtNodeReader {
-        protected static int readPtNodeOptionFlags(final DictBuffer dictBuffer) {
+    protected static class PtNodeReader extends DictDecoder.PtNodeReader {
+        private static int readFrequency(final DictBuffer dictBuffer) {
             return dictBuffer.readUnsignedByte();
         }
-
-        protected static int readParentAddress(final DictBuffer dictBuffer,
-                final FormatOptions formatOptions) {
-            if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
-                return BinaryDictDecoderUtils.readSInt24(dictBuffer);
-            } else {
-                return FormatSpec.NO_PARENT_ADDRESS;
-            }
-        }
-
-        protected static int readFrequency(final DictBuffer dictBuffer) {
-            return dictBuffer.readUnsignedByte();
-        }
-
-        protected static int readChildrenAddress(final DictBuffer dictBuffer, final int optionFlags,
-                final FormatOptions formatOptions) {
-            if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
-                final int address = BinaryDictDecoderUtils.readSInt24(dictBuffer);
-                if (address == 0) return FormatSpec.NO_CHILDREN_ADDRESS;
-                return address;
-            } else {
-                switch (optionFlags & FormatSpec.MASK_CHILDREN_ADDRESS_TYPE) {
-                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_ONEBYTE:
-                        return dictBuffer.readUnsignedByte();
-                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_TWOBYTES:
-                        return dictBuffer.readUnsignedShort();
-                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_THREEBYTES:
-                        return dictBuffer.readUnsignedInt24();
-                    case FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_NOADDRESS:
-                    default:
-                        return FormatSpec.NO_CHILDREN_ADDRESS;
-                }
-            }
-        }
-
-        // Reads shortcuts and returns the read length.
-        protected static int readShortcut(final DictBuffer dictBuffer,
-                final ArrayList<WeightedString> shortcutTargets) {
-            final int pointerBefore = dictBuffer.position();
-            dictBuffer.readUnsignedShort(); // skip the size
-            while (true) {
-                final int targetFlags = dictBuffer.readUnsignedByte();
-                final String word = CharEncoding.readString(dictBuffer);
-                shortcutTargets.add(new WeightedString(word,
-                        targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY));
-                if (0 == (targetFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
-            }
-            return dictBuffer.position() - pointerBefore;
-        }
-
-        protected static int readBigrams(final DictBuffer dictBuffer,
-                final ArrayList<PendingAttribute> bigrams, final int baseAddress) {
-            int readLength = 0;
-            int bigramCount = 0;
-            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
-                final int bigramFlags = dictBuffer.readUnsignedByte();
-                ++readLength;
-                final int sign = 0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_ATTR_OFFSET_NEGATIVE)
-                        ? 1 : -1;
-                int bigramAddress = baseAddress + readLength;
-                switch (bigramFlags & FormatSpec.MASK_BIGRAM_ATTR_ADDRESS_TYPE) {
-                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_ONEBYTE:
-                        bigramAddress += sign * dictBuffer.readUnsignedByte();
-                        readLength += 1;
-                        break;
-                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_TWOBYTES:
-                        bigramAddress += sign * dictBuffer.readUnsignedShort();
-                        readLength += 2;
-                        break;
-                    case FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_THREEBYTES:
-                        final int offset = (dictBuffer.readUnsignedByte() << 16)
-                                + dictBuffer.readUnsignedShort();
-                        bigramAddress += sign * offset;
-                        readLength += 3;
-                        break;
-                    default:
-                        throw new RuntimeException("Has bigrams with no address");
-                }
-                bigrams.add(new PendingAttribute(
-                        bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY,
-                        bigramAddress));
-                if (0 == (bigramFlags & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT)) break;
-            }
-            return readLength;
-        }
     }
 
     private final File mDictionaryBinaryFile;
@@ -199,7 +83,7 @@ public class Ver3DictDecoder implements DictDecoder {
     }
 
     @Override
-    public boolean isOpenedDictBuffer() {
+    public boolean isDictBufferOpen() {
         return mDictBuffer != null;
     }
 
@@ -218,25 +102,11 @@ public class Ver3DictDecoder implements DictDecoder {
         if (mDictBuffer == null) {
             openDictBuffer();
         }
-
-        final int version = HeaderReader.readVersion(mDictBuffer);
-        final int optionsFlags = HeaderReader.readOptionFlags(mDictBuffer);
-
-        final int headerSize = HeaderReader.readHeaderSize(mDictBuffer);
-
-        if (headerSize < 0) {
-            throw new UnsupportedFormatException("header size can't be negative.");
+        final FileHeader header = super.readHeader(mDictBuffer);
+        final int version = header.mFormatOptions.mVersion;
+        if (!(version >= 2 && version <= 3)) {
+          throw new UnsupportedFormatException("File header has a wrong version : " + version);
         }
-
-        final HashMap<String, String> attributes = HeaderReader.readAttributes(mDictBuffer,
-                headerSize);
-
-        final FileHeader header = new FileHeader(headerSize,
-                new FusionDictionary.DictionaryOptions(attributes,
-                        0 != (optionsFlags & FormatSpec.GERMAN_UMLAUT_PROCESSING_FLAG),
-                        0 != (optionsFlags & FormatSpec.FRENCH_LIGATURE_PROCESSING_FLAG)),
-                new FormatOptions(version,
-                        0 != (optionsFlags & FormatSpec.SUPPORTS_DYNAMIC_UPDATE)));
         return header;
     }
 
@@ -246,11 +116,11 @@ public class Ver3DictDecoder implements DictDecoder {
     public PtNodeInfo readPtNode(final int ptNodePos, final FormatOptions options) {
         int addressPointer = ptNodePos;
         final int flags = PtNodeReader.readPtNodeOptionFlags(mDictBuffer);
-        ++addressPointer;
+        addressPointer += FormatSpec.PTNODE_FLAGS_SIZE;
 
         final int parentAddress = PtNodeReader.readParentAddress(mDictBuffer, options);
         if (BinaryDictIOUtils.supportsDynamicUpdate(options)) {
-            addressPointer += 3;
+            addressPointer += FormatSpec.PARENT_ADDRESS_SIZE;
         }
 
         final int characters[];
@@ -258,7 +128,7 @@ public class Ver3DictDecoder implements DictDecoder {
             int index = 0;
             int character = CharEncoding.readChar(mDictBuffer);
             addressPointer += CharEncoding.getCharSize(character);
-            while (-1 != character) {
+            while (FormatSpec.INVALID_CHARACTER != character) {
                 // FusionDictionary is making sure that the length of the word is smaller than
                 // MAX_WORD_LENGTH.
                 // So we'll never write past the end of mCharacterBuffer.
@@ -274,8 +144,8 @@ public class Ver3DictDecoder implements DictDecoder {
         }
         final int frequency;
         if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
-            ++addressPointer;
             frequency = PtNodeReader.readFrequency(mDictBuffer);
+            addressPointer += FormatSpec.PTNODE_FREQUENCY_SIZE;
         } else {
             frequency = PtNode.NOT_A_TERMINAL;
         }
@@ -296,7 +166,8 @@ public class Ver3DictDecoder implements DictDecoder {
         final ArrayList<PendingAttribute> bigrams;
         if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
             bigrams = new ArrayList<PendingAttribute>();
-            addressPointer += PtNodeReader.readBigrams(mDictBuffer, bigrams, addressPointer);
+            addressPointer += PtNodeReader.readBigramAddresses(mDictBuffer, bigrams, 
+                    addressPointer);
             if (bigrams.size() >= FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
                 MakedictLog.d("too many bigrams in a PtNode.");
             }
@@ -332,25 +203,6 @@ public class Ver3DictDecoder implements DictDecoder {
     }
 
     @Override
-    public int getTerminalPosition(String word) throws IOException, UnsupportedFormatException {
-        if (mDictBuffer == null) {
-            openDictBuffer();
-        }
-        return BinaryDictIOUtils.getTerminalPosition(this, word);
-    }
-
-    @Override
-    public void readUnigramsAndBigramsBinary(final TreeMap<Integer, String> words,
-            final TreeMap<Integer, Integer> frequencies,
-            final TreeMap<Integer, ArrayList<PendingAttribute>> bigrams)
-            throws IOException, UnsupportedFormatException {
-        if (mDictBuffer == null) {
-            openDictBuffer();
-        }
-        BinaryDictIOUtils.readUnigramsAndBigramsBinary(this, words, frequencies, bigrams);
-    }
-
-    @Override
     public void setPosition(int newPos) {
         mDictBuffer.position(newPos);
     }
@@ -366,7 +218,7 @@ public class Ver3DictDecoder implements DictDecoder {
     }
 
     @Override
-    public boolean readForwardLinkAndAdvancePosition() {
+    public boolean readAndFollowForwardLink() {
         final int nextAddress = mDictBuffer.readUnsignedInt24();
         if (nextAddress >= 0 && nextAddress < mDictBuffer.limit()) {
             mDictBuffer.position(nextAddress);
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver3DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver3DictEncoder.java
index 222a0f474..76f0f4052 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver3DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver3DictEncoder.java
@@ -167,7 +167,7 @@ public class Ver3DictEncoder implements DictEncoder {
         }
     }
 
-    public void writeChildrenPosition(final PtNode ptNode, final FormatOptions formatOptions) {
+    private void writeChildrenPosition(final PtNode ptNode, final FormatOptions formatOptions) {
         final int childrenPos = BinaryDictEncoderUtils.getChildrenPosition(ptNode, formatOptions);
         if (formatOptions.mSupportsDynamicUpdate) {
             mPosition += BinaryDictEncoderUtils.writeSignedChildrenPosition(mBuffer, mPosition,
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
new file mode 100644
index 000000000..36c5a2720
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
@@ -0,0 +1,259 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin.makedict;
+
+import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.CharEncoding;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.DictBuffer;
+import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
+import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
+import com.android.inputmethod.latin.makedict.FusionDictionary.PtNode;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Arrays;
+
+/**
+ * An implementation of binary dictionary decoder for version 4 binary dictionary.
+ */
+@UsedForTesting
+public class Ver4DictDecoder extends DictDecoder {
+    private static final String TAG = Ver4DictDecoder.class.getSimpleName();
+
+    private static final int FILETYPE_TRIE = 1;
+    private static final int FILETYPE_FREQUENCY = 2;
+
+    private final File mDictDirectory;
+    private final DictionaryBufferFactory mBufferFactory;
+    private DictBuffer mDictBuffer;
+    private DictBuffer mFrequencyBuffer;
+
+    @UsedForTesting
+    /* package */ Ver4DictDecoder(final File dictDirectory, final int factoryFlag) {
+        mDictDirectory = dictDirectory;
+        mDictBuffer = mFrequencyBuffer = null;
+
+        if ((factoryFlag & MASK_DICTBUFFER) == USE_READONLY_BYTEBUFFER) {
+            mBufferFactory = new DictionaryBufferFromReadOnlyByteBufferFactory();
+        } else if ((factoryFlag  & MASK_DICTBUFFER) == USE_BYTEARRAY) {
+            mBufferFactory = new DictionaryBufferFromByteArrayFactory();
+        } else if ((factoryFlag & MASK_DICTBUFFER) == USE_WRITABLE_BYTEBUFFER) {
+            mBufferFactory = new DictionaryBufferFromWritableByteBufferFactory();
+        } else {
+            mBufferFactory = new DictionaryBufferFromReadOnlyByteBufferFactory();
+        }
+    }
+
+    @UsedForTesting
+    /* package */ Ver4DictDecoder(final File dictDirectory, final DictionaryBufferFactory factory) {
+        mDictDirectory = dictDirectory;
+        mBufferFactory = factory;
+        mDictBuffer = mFrequencyBuffer = null;
+    }
+
+    private File getFile(final int fileType) {
+        if (fileType == FILETYPE_TRIE) {
+            return new File(mDictDirectory,
+                    mDictDirectory.getName() + FormatSpec.TRIE_FILE_EXTENSION);
+        } else if (fileType == FILETYPE_FREQUENCY) {
+            return new File(mDictDirectory,
+                    mDictDirectory.getName() + FormatSpec.FREQ_FILE_EXTENSION);
+        } else {
+            throw new RuntimeException("Unsupported kind of file : " + fileType);
+        }
+    }
+
+    @Override
+    public void openDictBuffer() throws FileNotFoundException, IOException {
+        final String filename = mDictDirectory.getName();
+        mDictBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_TRIE));
+        mFrequencyBuffer = mBufferFactory.getDictionaryBuffer(getFile(FILETYPE_FREQUENCY));
+    }
+
+    @Override
+    public boolean isDictBufferOpen() {
+        return mDictBuffer != null;
+    }
+
+    /* package */ DictBuffer getDictBuffer() {
+        return mDictBuffer;
+    }
+
+    @Override
+    public FileHeader readHeader() throws IOException, UnsupportedFormatException {
+        if (mDictBuffer == null) {
+            openDictBuffer();
+        }
+        final FileHeader header = super.readHeader(mDictBuffer);
+        final int version = header.mFormatOptions.mVersion;
+        if (version != 4) {
+            throw new UnsupportedFormatException("File header has a wrong version : " + version);
+        }
+        return header;
+    }
+
+    protected static class PtNodeReader extends DictDecoder.PtNodeReader {
+        protected static int readFrequency(final DictBuffer frequencyBuffer, final int terminalId) {
+            frequencyBuffer.position(terminalId * FormatSpec.FREQUENCY_AND_FLAGS_SIZE + 1);
+            return frequencyBuffer.readUnsignedByte();
+        }
+
+        protected static int readTerminalId(final DictBuffer dictBuffer) {
+            return dictBuffer.readInt();
+        }
+    }
+
+    // TODO: Make this buffer thread safe.
+    // TODO: Support words longer than FormatSpec.MAX_WORD_LENGTH.
+    private final int[] mCharacterBuffer = new int[FormatSpec.MAX_WORD_LENGTH];
+    @Override
+    public PtNodeInfo readPtNode(int ptNodePos, FormatOptions options) {
+        int addressPointer = ptNodePos;
+        final int flags = PtNodeReader.readPtNodeOptionFlags(mDictBuffer);
+        addressPointer += FormatSpec.PTNODE_FLAGS_SIZE;
+
+        final int parentAddress = PtNodeReader.readParentAddress(mDictBuffer, options);
+        if (BinaryDictIOUtils.supportsDynamicUpdate(options)) {
+            addressPointer += FormatSpec.PARENT_ADDRESS_SIZE;
+        }
+
+        final int characters[];
+        if (0 != (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS)) {
+            int index = 0;
+            int character = CharEncoding.readChar(mDictBuffer);
+            addressPointer += CharEncoding.getCharSize(character);
+            while (FormatSpec.INVALID_CHARACTER != character
+                    && index < FormatSpec.MAX_WORD_LENGTH) {
+                mCharacterBuffer[index++] = character;
+                character = CharEncoding.readChar(mDictBuffer);
+                addressPointer += CharEncoding.getCharSize(character);
+            }
+            characters = Arrays.copyOfRange(mCharacterBuffer, 0, index);
+        } else {
+            final int character = CharEncoding.readChar(mDictBuffer);
+            addressPointer += CharEncoding.getCharSize(character);
+            characters = new int[] { character };
+        }
+        final int terminalId;
+        if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
+            terminalId = PtNodeReader.readTerminalId(mDictBuffer);
+            addressPointer += FormatSpec.PTNODE_TERMINAL_ID_SIZE;
+        } else {
+            terminalId = PtNode.NOT_A_TERMINAL;
+        }
+
+        final int frequency;
+        if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
+            frequency = PtNodeReader.readFrequency(mFrequencyBuffer, terminalId);
+        } else {
+            frequency = PtNode.NOT_A_TERMINAL;
+        }
+        int childrenAddress = PtNodeReader.readChildrenAddress(mDictBuffer, flags, options);
+        if (childrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
+            childrenAddress += addressPointer;
+        }
+        addressPointer += BinaryDictIOUtils.getChildrenAddressSize(flags, options);
+        final ArrayList<WeightedString> shortcutTargets;
+        if (0 != (flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)) {
+            // readShortcut will add shortcuts to shortcutTargets.
+            shortcutTargets = new ArrayList<WeightedString>();
+            addressPointer += PtNodeReader.readShortcut(mDictBuffer, shortcutTargets);
+        } else {
+            shortcutTargets = null;
+        }
+
+        final ArrayList<PendingAttribute> bigrams;
+        if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
+            bigrams = new ArrayList<PendingAttribute>();
+            addressPointer += PtNodeReader.readBigramAddresses(mDictBuffer, bigrams,
+                    addressPointer);
+            if (bigrams.size() >= FormatSpec.MAX_BIGRAMS_IN_A_PTNODE) {
+                MakedictLog.d("too many bigrams in a node.");
+            }
+        } else {
+            bigrams = null;
+        }
+        return new PtNodeInfo(ptNodePos, addressPointer, flags, characters, frequency,
+                parentAddress, childrenAddress, shortcutTargets, bigrams);
+    }
+
+    private void deleteDictFiles() {
+        final File[] files = mDictDirectory.listFiles();
+        for (int i = 0; i < files.length; ++i) {
+            files[i].delete();
+        }
+    }
+
+    @Override
+    public FusionDictionary readDictionaryBinary(final FusionDictionary dict,
+            final boolean deleteDictIfBroken)
+            throws FileNotFoundException, IOException, UnsupportedFormatException {
+        if (mDictBuffer == null) {
+            openDictBuffer();
+        }
+        try {
+            return BinaryDictDecoderUtils.readDictionaryBinary(this, dict);
+        } catch (IOException e) {
+            Log.e(TAG, "The dictionary " + mDictDirectory.getName() + " is broken.", e);
+            if (deleteDictIfBroken) {
+                deleteDictFiles();
+            }
+            throw e;
+        } catch (UnsupportedFormatException e) {
+            Log.e(TAG, "The dictionary " + mDictDirectory.getName() + " is broken.", e);
+            if (deleteDictIfBroken) {
+                deleteDictFiles();
+            }
+            throw e;
+        }
+    }
+
+    @Override
+    public void setPosition(int newPos) {
+        mDictBuffer.position(newPos);
+    }
+
+    @Override
+    public int getPosition() {
+        return mDictBuffer.position();
+    }
+
+    @Override
+    public int readPtNodeCount() {
+        return BinaryDictDecoderUtils.readPtNodeCount(mDictBuffer);
+    }
+
+    @Override
+    public boolean readAndFollowForwardLink() {
+        final int nextAddress = mDictBuffer.readUnsignedInt24();
+        if (nextAddress >= 0 && nextAddress < mDictBuffer.limit()) {
+            mDictBuffer.position(nextAddress);
+            return true;
+        }
+        return false;
+    }
+
+    @Override
+    public boolean hasNextPtNodeArray() {
+        return mDictBuffer.position() != FormatSpec.NO_FORWARD_LINK_ADDRESS;
+    }
+}