[Refactor] Divide BinaryDictInputOutput into BinaryDictEncoder and BinaryDictDecoder.

Change-Id: I7c3269d77e3e3b567e459dcaa1bc029903941744

9 files changed, 896 insertions, 850 deletions

diff --git a/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
index d0a4afd50..7e497e9b9 100644
--- a/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
+++ b/java/src/com/android/inputmethod/latin/BinaryDictionaryGetter.java
@@ -21,7 +21,7 @@ import android.content.SharedPreferences;
 import android.content.res.AssetFileDescriptor;
 import android.util.Log;
 
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder;
 import com.android.inputmethod.latin.makedict.FormatSpec;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 import com.android.inputmethod.latin.utils.DictionaryInfoUtils;
@@ -231,8 +231,8 @@ final public class BinaryDictionaryGetter {
         try {
             // Read the version of the file
             inStream = new FileInputStream(f);
-            final BinaryDictInputOutput.ByteBufferWrapper buffer =
-                    new BinaryDictInputOutput.ByteBufferWrapper(inStream.getChannel().map(
+            final BinaryDictDecoder.ByteBufferWrapper buffer =
+                    new BinaryDictDecoder.ByteBufferWrapper(inStream.getChannel().map(
                             FileChannel.MapMode.READ_ONLY, 0, f.length()));
             final int magic = buffer.readInt();
             if (magic != FormatSpec.MAGIC_NUMBER) {
@@ -241,7 +241,7 @@ final public class BinaryDictionaryGetter {
             final int formatVersion = buffer.readInt();
             final int headerSize = buffer.readInt();
             final HashMap<String, String> options = CollectionUtils.newHashMap();
-            BinaryDictInputOutput.populateOptions(buffer, headerSize, options);
+            BinaryDictDecoder.populateOptions(buffer, headerSize, options);
 
             final String version = options.get(VERSION_KEY);
             if (null == version) {
diff --git a/java/src/com/android/inputmethod/latin/DictionaryWriter.java b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
index 47151bf61..3b300a3fd 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryWriter.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
@@ -20,7 +20,7 @@ import android.content.Context;
 
 import com.android.inputmethod.keyboard.ProximityInfo;
 import com.android.inputmethod.latin.SuggestedWords.SuggestedWordInfo;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput;
+import com.android.inputmethod.latin.makedict.BinaryDictEncoder;
 import com.android.inputmethod.latin.makedict.FormatSpec;
 import com.android.inputmethod.latin.makedict.FusionDictionary;
 import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
@@ -87,7 +87,7 @@ public class DictionaryWriter extends AbstractDictionaryWriter {
     @Override
     protected void writeBinaryDictionary(final FileOutputStream out)
             throws IOException, UnsupportedFormatException {
-        BinaryDictInputOutput.writeDictionaryBinary(out, mFusionDictionary, FORMAT_OPTIONS);
+        BinaryDictEncoder.writeDictionaryBinary(out, mFusionDictionary, FORMAT_OPTIONS);
     }
 
     @Override
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java
new file mode 100644
index 000000000..767f4fc72
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoder.java
@@ -0,0 +1,819 @@
+/*
+ * 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.FormatSpec.FileHeader;
+import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
+import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+import com.android.inputmethod.latin.utils.JniUtils;
+
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.nio.channels.FileChannel;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+
+/**
+ * Decodes binary files for a FusionDictionary.
+ *
+ * All the methods in this class are static.
+ */
+public final class BinaryDictDecoder {
+
+    private static final boolean DBG = MakedictLog.DBG;
+
+    static {
+        JniUtils.loadNativeLibrary();
+    }
+
+    // TODO: implement something sensical instead of just a phony method
+    private static native int doNothing();
+
+    private BinaryDictDecoder() {
+        // This utility class is not publicly instantiable.
+    }
+
+    private static final int MAX_JUMPS = 12;
+
+    @UsedForTesting
+    public interface FusionDictionaryBufferInterface {
+        public int readUnsignedByte();
+        public int readUnsignedShort();
+        public int readUnsignedInt24();
+        public int readInt();
+        public int position();
+        public void position(int newPosition);
+        public void put(final byte b);
+        public int limit();
+        @UsedForTesting
+        public int capacity();
+    }
+
+    public static final class ByteBufferWrapper implements FusionDictionaryBufferInterface {
+        private ByteBuffer mBuffer;
+
+        public ByteBufferWrapper(final ByteBuffer buffer) {
+            mBuffer = buffer;
+        }
+
+        @Override
+        public int readUnsignedByte() {
+            return mBuffer.get() & 0xFF;
+        }
+
+        @Override
+        public int readUnsignedShort() {
+            return mBuffer.getShort() & 0xFFFF;
+        }
+
+        @Override
+        public int readUnsignedInt24() {
+            final int retval = readUnsignedByte();
+            return (retval << 16) + readUnsignedShort();
+        }
+
+        @Override
+        public int readInt() {
+            return mBuffer.getInt();
+        }
+
+        @Override
+        public int position() {
+            return mBuffer.position();
+        }
+
+        @Override
+        public void position(int newPos) {
+            mBuffer.position(newPos);
+        }
+
+        @Override
+        public void put(final byte b) {
+            mBuffer.put(b);
+        }
+
+        @Override
+        public int limit() {
+            return mBuffer.limit();
+        }
+
+        @Override
+        public int capacity() {
+            return mBuffer.capacity();
+        }
+    }
+
+    /**
+     * A class grouping utility function for our specific character encoding.
+     */
+    static final class CharEncoding {
+        private static final int MINIMAL_ONE_BYTE_CHARACTER_VALUE = 0x20;
+        private static final int MAXIMAL_ONE_BYTE_CHARACTER_VALUE = 0xFF;
+
+        /**
+         * Helper method to find out whether this code fits on one byte
+         */
+        private static boolean fitsOnOneByte(final int character) {
+            return character >= MINIMAL_ONE_BYTE_CHARACTER_VALUE
+                    && character <= MAXIMAL_ONE_BYTE_CHARACTER_VALUE;
+        }
+
+        /**
+         * Compute the size of a character given its character code.
+         *
+         * Char format is:
+         * 1 byte = bbbbbbbb match
+         * case 000xxxxx: xxxxx << 16 + next byte << 8 + next byte
+         * else: if 00011111 (= 0x1F) : this is the terminator. This is a relevant choice because
+         *       unicode code points range from 0 to 0x10FFFF, so any 3-byte value starting with
+         *       00011111 would be outside unicode.
+         * else: iso-latin-1 code
+         * This allows for the whole unicode range to be encoded, including chars outside of
+         * the BMP. Also everything in the iso-latin-1 charset is only 1 byte, except control
+         * characters which should never happen anyway (and still work, but take 3 bytes).
+         *
+         * @param character the character code.
+         * @return the size in binary encoded-form, either 1 or 3 bytes.
+         */
+        static int getCharSize(final int character) {
+            // See char encoding in FusionDictionary.java
+            if (fitsOnOneByte(character)) return 1;
+            if (FormatSpec.INVALID_CHARACTER == character) return 1;
+            return 3;
+        }
+
+        /**
+         * Compute the byte size of a character array.
+         */
+        static int getCharArraySize(final int[] chars) {
+            int size = 0;
+            for (int character : chars) size += getCharSize(character);
+            return size;
+        }
+
+        /**
+         * Writes a char array to a byte buffer.
+         *
+         * @param codePoints the code point array to write.
+         * @param buffer the byte buffer to write to.
+         * @param index the index in buffer to write the character array to.
+         * @return the index after the last character.
+         */
+        static int writeCharArray(final int[] codePoints, final byte[] buffer, int index) {
+            for (int codePoint : codePoints) {
+                if (1 == getCharSize(codePoint)) {
+                    buffer[index++] = (byte)codePoint;
+                } else {
+                    buffer[index++] = (byte)(0xFF & (codePoint >> 16));
+                    buffer[index++] = (byte)(0xFF & (codePoint >> 8));
+                    buffer[index++] = (byte)(0xFF & codePoint);
+                }
+            }
+            return index;
+        }
+
+        /**
+         * Writes a string with our character format to a byte buffer.
+         *
+         * This will also write the terminator byte.
+         *
+         * @param buffer the byte buffer to write to.
+         * @param origin the offset to write from.
+         * @param word the string to write.
+         * @return the size written, in bytes.
+         */
+        static int writeString(final byte[] buffer, final int origin,
+                final String word) {
+            final int length = word.length();
+            int index = origin;
+            for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
+                final int codePoint = word.codePointAt(i);
+                if (1 == getCharSize(codePoint)) {
+                    buffer[index++] = (byte)codePoint;
+                } else {
+                    buffer[index++] = (byte)(0xFF & (codePoint >> 16));
+                    buffer[index++] = (byte)(0xFF & (codePoint >> 8));
+                    buffer[index++] = (byte)(0xFF & codePoint);
+                }
+            }
+            buffer[index++] = FormatSpec.GROUP_CHARACTERS_TERMINATOR;
+            return index - origin;
+        }
+
+        /**
+         * Writes a string with our character format to a ByteArrayOutputStream.
+         *
+         * This will also write the terminator byte.
+         *
+         * @param buffer the ByteArrayOutputStream to write to.
+         * @param word the string to write.
+         */
+        static void writeString(final ByteArrayOutputStream buffer, final String word) {
+            final int length = word.length();
+            for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
+                final int codePoint = word.codePointAt(i);
+                if (1 == getCharSize(codePoint)) {
+                    buffer.write((byte) codePoint);
+                } else {
+                    buffer.write((byte) (0xFF & (codePoint >> 16)));
+                    buffer.write((byte) (0xFF & (codePoint >> 8)));
+                    buffer.write((byte) (0xFF & codePoint));
+                }
+            }
+            buffer.write(FormatSpec.GROUP_CHARACTERS_TERMINATOR);
+        }
+
+        /**
+         * Reads a string from a buffer. This is the converse of the above method.
+         */
+        private static String readString(final FusionDictionaryBufferInterface buffer) {
+            final StringBuilder s = new StringBuilder();
+            int character = readChar(buffer);
+            while (character != FormatSpec.INVALID_CHARACTER) {
+                s.appendCodePoint(character);
+                character = readChar(buffer);
+            }
+            return s.toString();
+        }
+
+        /**
+         * Reads a character from the buffer.
+         *
+         * This follows the character format documented earlier in this source file.
+         *
+         * @param buffer the buffer, positioned over an encoded character.
+         * @return the character code.
+         */
+        static int readChar(final FusionDictionaryBufferInterface buffer) {
+            int character = buffer.readUnsignedByte();
+            if (!fitsOnOneByte(character)) {
+                if (FormatSpec.GROUP_CHARACTERS_TERMINATOR == character) {
+                    return FormatSpec.INVALID_CHARACTER;
+                }
+                character <<= 16;
+                character += buffer.readUnsignedShort();
+            }
+            return character;
+        }
+    }
+
+    // Input methods: Read a binary dictionary to memory.
+    // readDictionaryBinary is the public entry point for them.
+
+    static int readChildrenAddress(final FusionDictionaryBufferInterface buffer,
+            final int optionFlags, final FormatOptions options) {
+        if (options.mSupportsDynamicUpdate) {
+            final int address = buffer.readUnsignedInt24();
+            if (address == 0) return FormatSpec.NO_CHILDREN_ADDRESS;
+            if ((address & FormatSpec.MSB24) != 0) {
+                return -(address & FormatSpec.SINT24_MAX);
+            } else {
+                return address;
+            }
+        }
+        int address;
+        switch (optionFlags & FormatSpec.MASK_GROUP_ADDRESS_TYPE) {
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
+                return buffer.readUnsignedByte();
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
+                return buffer.readUnsignedShort();
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
+                return buffer.readUnsignedInt24();
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
+            default:
+                return FormatSpec.NO_CHILDREN_ADDRESS;
+        }
+    }
+
+    static int readParentAddress(final FusionDictionaryBufferInterface buffer,
+            final FormatOptions formatOptions) {
+        if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
+            final int parentAddress = buffer.readUnsignedInt24();
+            final int sign = ((parentAddress & FormatSpec.MSB24) != 0) ? -1 : 1;
+            return sign * (parentAddress & FormatSpec.SINT24_MAX);
+        } else {
+            return FormatSpec.NO_PARENT_ADDRESS;
+        }
+    }
+
+    private static final int[] CHARACTER_BUFFER = new int[FormatSpec.MAX_WORD_LENGTH];
+    public static CharGroupInfo readCharGroup(final FusionDictionaryBufferInterface buffer,
+            final int originalGroupAddress, final FormatOptions options) {
+        int addressPointer = originalGroupAddress;
+        final int flags = buffer.readUnsignedByte();
+        ++addressPointer;
+
+        final int parentAddress = readParentAddress(buffer, options);
+        if (BinaryDictIOUtils.supportsDynamicUpdate(options)) {
+            addressPointer += 3;
+        }
+
+        final int characters[];
+        if (0 != (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS)) {
+            int index = 0;
+            int character = CharEncoding.readChar(buffer);
+            addressPointer += CharEncoding.getCharSize(character);
+            while (-1 != 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 CHARACTER_BUFFER.
+                CHARACTER_BUFFER[index++] = character;
+                character = CharEncoding.readChar(buffer);
+                addressPointer += CharEncoding.getCharSize(character);
+            }
+            characters = Arrays.copyOfRange(CHARACTER_BUFFER, 0, index);
+        } else {
+            final int character = CharEncoding.readChar(buffer);
+            addressPointer += CharEncoding.getCharSize(character);
+            characters = new int[] { character };
+        }
+        final int frequency;
+        if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
+            ++addressPointer;
+            frequency = buffer.readUnsignedByte();
+        } else {
+            frequency = CharGroup.NOT_A_TERMINAL;
+        }
+        int childrenAddress = readChildrenAddress(buffer, flags, options);
+        if (childrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
+            childrenAddress += addressPointer;
+        }
+        addressPointer += BinaryDictIOUtils.getChildrenAddressSize(flags, options);
+        ArrayList<WeightedString> shortcutTargets = null;
+        if (0 != (flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)) {
+            final int pointerBefore = buffer.position();
+            shortcutTargets = new ArrayList<WeightedString>();
+            buffer.readUnsignedShort(); // Skip the size
+            while (true) {
+                final int targetFlags = buffer.readUnsignedByte();
+                final String word = CharEncoding.readString(buffer);
+                shortcutTargets.add(new WeightedString(word,
+                        targetFlags & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY));
+                if (0 == (targetFlags & FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT)) break;
+            }
+            addressPointer += buffer.position() - pointerBefore;
+        }
+        ArrayList<PendingAttribute> bigrams = null;
+        if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
+            bigrams = new ArrayList<PendingAttribute>();
+            int bigramCount = 0;
+            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
+                final int bigramFlags = buffer.readUnsignedByte();
+                ++addressPointer;
+                final int sign = 0 == (bigramFlags & FormatSpec.FLAG_ATTRIBUTE_OFFSET_NEGATIVE)
+                        ? 1 : -1;
+                int bigramAddress = addressPointer;
+                switch (bigramFlags & FormatSpec.MASK_ATTRIBUTE_ADDRESS_TYPE) {
+                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
+                    bigramAddress += sign * buffer.readUnsignedByte();
+                    addressPointer += 1;
+                    break;
+                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
+                    bigramAddress += sign * buffer.readUnsignedShort();
+                    addressPointer += 2;
+                    break;
+                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
+                    final int offset = (buffer.readUnsignedByte() << 16)
+                            + buffer.readUnsignedShort();
+                    bigramAddress += sign * offset;
+                    addressPointer += 3;
+                    break;
+                default:
+                    throw new RuntimeException("Has bigrams with no address");
+                }
+                bigrams.add(new PendingAttribute(bigramFlags & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY,
+                        bigramAddress));
+                if (0 == (bigramFlags & FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT)) break;
+            }
+            if (bigramCount >= FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
+                MakedictLog.d("too many bigrams in a group.");
+            }
+        }
+        return new CharGroupInfo(originalGroupAddress, addressPointer, flags, characters, frequency,
+                parentAddress, childrenAddress, shortcutTargets, bigrams);
+    }
+
+    /**
+     * Reads and returns the char group count out of a buffer and forwards the pointer.
+     */
+    public static int readCharGroupCount(final FusionDictionaryBufferInterface buffer) {
+        final int msb = buffer.readUnsignedByte();
+        if (FormatSpec.MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT >= msb) {
+            return msb;
+        } else {
+            return ((FormatSpec.MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT & msb) << 8)
+                    + buffer.readUnsignedByte();
+        }
+    }
+
+    // The word cache here is a stopgap bandaid to help the catastrophic performance
+    // of this method. Since it performs direct, unbuffered random access to the file and
+    // may be called hundreds of thousands of times, the resulting performance is not
+    // reasonable without some kind of cache. Thus:
+    private static TreeMap<Integer, WeightedString> wordCache =
+            new TreeMap<Integer, WeightedString>();
+    /**
+     * Finds, as a string, the word at the address passed as an argument.
+     *
+     * @param buffer the buffer to read from.
+     * @param headerSize the size of the header.
+     * @param address the address to seek.
+     * @param formatOptions file format options.
+     * @return the word with its frequency, as a weighted string.
+     */
+    /* package for tests */ static WeightedString getWordAtAddress(
+            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
+            final FormatOptions formatOptions) {
+        final WeightedString cachedString = wordCache.get(address);
+        if (null != cachedString) return cachedString;
+
+        final WeightedString result;
+        final int originalPointer = buffer.position();
+        buffer.position(address);
+
+        if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
+            result = getWordAtAddressWithParentAddress(buffer, headerSize, address, formatOptions);
+        } else {
+            result = getWordAtAddressWithoutParentAddress(buffer, headerSize, address,
+                    formatOptions);
+        }
+
+        wordCache.put(address, result);
+        buffer.position(originalPointer);
+        return result;
+    }
+
+    // TODO: static!? This will behave erratically when used in multi-threaded code.
+    // We need to fix this
+    private static int[] sGetWordBuffer = new int[FormatSpec.MAX_WORD_LENGTH];
+    @SuppressWarnings("unused")
+    private static WeightedString getWordAtAddressWithParentAddress(
+            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
+            final FormatOptions options) {
+        int currentAddress = address;
+        int index = FormatSpec.MAX_WORD_LENGTH - 1;
+        int frequency = Integer.MIN_VALUE;
+        // the length of the path from the root to the leaf is limited by MAX_WORD_LENGTH
+        for (int count = 0; count < FormatSpec.MAX_WORD_LENGTH; ++count) {
+            CharGroupInfo currentInfo;
+            int loopCounter = 0;
+            do {
+                buffer.position(currentAddress + headerSize);
+                currentInfo = readCharGroup(buffer, currentAddress, options);
+                if (BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags, options)) {
+                    currentAddress = currentInfo.mParentAddress + currentInfo.mOriginalAddress;
+                }
+                if (DBG && loopCounter++ > MAX_JUMPS) {
+                    MakedictLog.d("Too many jumps - probably a bug");
+                }
+            } while (BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags, options));
+            if (Integer.MIN_VALUE == frequency) frequency = currentInfo.mFrequency;
+            for (int i = 0; i < currentInfo.mCharacters.length; ++i) {
+                sGetWordBuffer[index--] =
+                        currentInfo.mCharacters[currentInfo.mCharacters.length - i - 1];
+            }
+            if (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS) break;
+            currentAddress = currentInfo.mParentAddress + currentInfo.mOriginalAddress;
+        }
+
+        return new WeightedString(
+                new String(sGetWordBuffer, index + 1, FormatSpec.MAX_WORD_LENGTH - index - 1),
+                        frequency);
+    }
+
+    private static WeightedString getWordAtAddressWithoutParentAddress(
+            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
+            final FormatOptions options) {
+        buffer.position(headerSize);
+        final int count = readCharGroupCount(buffer);
+        int groupOffset = BinaryDictIOUtils.getGroupCountSize(count);
+        final StringBuilder builder = new StringBuilder();
+        WeightedString result = null;
+
+        CharGroupInfo last = null;
+        for (int i = count - 1; i >= 0; --i) {
+            CharGroupInfo info = readCharGroup(buffer, groupOffset, options);
+            groupOffset = info.mEndAddress;
+            if (info.mOriginalAddress == address) {
+                builder.append(new String(info.mCharacters, 0, info.mCharacters.length));
+                result = new WeightedString(builder.toString(), info.mFrequency);
+                break; // and return
+            }
+            if (BinaryDictIOUtils.hasChildrenAddress(info.mChildrenAddress)) {
+                if (info.mChildrenAddress > address) {
+                    if (null == last) continue;
+                    builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
+                    buffer.position(last.mChildrenAddress + headerSize);
+                    i = readCharGroupCount(buffer);
+                    groupOffset = last.mChildrenAddress + BinaryDictIOUtils.getGroupCountSize(i);
+                    last = null;
+                    continue;
+                }
+                last = info;
+            }
+            if (0 == i && BinaryDictIOUtils.hasChildrenAddress(last.mChildrenAddress)) {
+                builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
+                buffer.position(last.mChildrenAddress + headerSize);
+                i = readCharGroupCount(buffer);
+                groupOffset = last.mChildrenAddress + BinaryDictIOUtils.getGroupCountSize(i);
+                last = null;
+                continue;
+            }
+        }
+        return result;
+    }
+
+    /**
+     * Reads a single node from a buffer.
+     *
+     * This methods reads the file at the current position. A node is fully expected to start at
+     * the current position.
+     * This will recursively read other nodes into the structure, populating the reverse
+     * maps on the fly and using them to keep track of already read nodes.
+     *
+     * @param buffer the buffer, correctly positioned at the start of a node.
+     * @param headerSize the size, in bytes, of the file header.
+     * @param reverseNodeMap a mapping from addresses to already read nodes.
+     * @param reverseGroupMap a mapping from addresses to already read character groups.
+     * @param options file format options.
+     * @return the read node with all his children already read.
+     */
+    private static Node readNode(final FusionDictionaryBufferInterface buffer, final int headerSize,
+            final Map<Integer, Node> reverseNodeMap, final Map<Integer, CharGroup> reverseGroupMap,
+            final FormatOptions options)
+            throws IOException {
+        final ArrayList<CharGroup> nodeContents = new ArrayList<CharGroup>();
+        final int nodeOrigin = buffer.position() - headerSize;
+
+        do { // Scan the linked-list node.
+            final int nodeHeadPosition = buffer.position() - headerSize;
+            final int count = readCharGroupCount(buffer);
+            int groupOffset = nodeHeadPosition + BinaryDictIOUtils.getGroupCountSize(count);
+            for (int i = count; i > 0; --i) { // Scan the array of CharGroup.
+                CharGroupInfo info = readCharGroup(buffer, groupOffset, options);
+                if (BinaryDictIOUtils.isMovedGroup(info.mFlags, options)) continue;
+                ArrayList<WeightedString> shortcutTargets = info.mShortcutTargets;
+                ArrayList<WeightedString> bigrams = null;
+                if (null != info.mBigrams) {
+                    bigrams = new ArrayList<WeightedString>();
+                    for (PendingAttribute bigram : info.mBigrams) {
+                        final WeightedString word = getWordAtAddress(
+                                buffer, headerSize, bigram.mAddress, options);
+                        final int reconstructedFrequency =
+                                reconstructBigramFrequency(word.mFrequency, bigram.mFrequency);
+                        bigrams.add(new WeightedString(word.mWord, reconstructedFrequency));
+                    }
+                }
+                if (BinaryDictIOUtils.hasChildrenAddress(info.mChildrenAddress)) {
+                    Node children = reverseNodeMap.get(info.mChildrenAddress);
+                    if (null == children) {
+                        final int currentPosition = buffer.position();
+                        buffer.position(info.mChildrenAddress + headerSize);
+                        children = readNode(
+                                buffer, headerSize, reverseNodeMap, reverseGroupMap, options);
+                        buffer.position(currentPosition);
+                    }
+                    nodeContents.add(
+                            new CharGroup(info.mCharacters, shortcutTargets, bigrams,
+                                    info.mFrequency,
+                                    0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
+                                    0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED), children));
+                } else {
+                    nodeContents.add(
+                            new CharGroup(info.mCharacters, shortcutTargets, bigrams,
+                                    info.mFrequency,
+                                    0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
+                                    0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED)));
+                }
+                groupOffset = info.mEndAddress;
+            }
+
+            // reach the end of the array.
+            if (options.mSupportsDynamicUpdate) {
+                final int nextAddress = buffer.readUnsignedInt24();
+                if (nextAddress >= 0 && nextAddress < buffer.limit()) {
+                    buffer.position(nextAddress);
+                } else {
+                    break;
+                }
+            }
+        } while (options.mSupportsDynamicUpdate &&
+                buffer.position() != FormatSpec.NO_FORWARD_LINK_ADDRESS);
+
+        final Node node = new Node(nodeContents);
+        node.mCachedAddressBeforeUpdate = nodeOrigin;
+        node.mCachedAddressAfterUpdate = nodeOrigin;
+        reverseNodeMap.put(node.mCachedAddressAfterUpdate, node);
+        return node;
+    }
+
+    /**
+     * Helper function to get the binary format version from the header.
+     * @throws IOException
+     */
+    private static int getFormatVersion(final FusionDictionaryBufferInterface buffer)
+            throws IOException {
+        final int magic = buffer.readInt();
+        if (FormatSpec.MAGIC_NUMBER == magic) return buffer.readUnsignedShort();
+        return FormatSpec.NOT_A_VERSION_NUMBER;
+    }
+
+    /**
+     * Helper function to get and validate the binary format version.
+     * @throws UnsupportedFormatException
+     * @throws IOException
+     */
+    private static int checkFormatVersion(final FusionDictionaryBufferInterface buffer)
+            throws IOException, UnsupportedFormatException {
+        final int version = getFormatVersion(buffer);
+        if (version < FormatSpec.MINIMUM_SUPPORTED_VERSION
+                || version > FormatSpec.MAXIMUM_SUPPORTED_VERSION) {
+            throw new UnsupportedFormatException("This file has version " + version
+                    + ", but this implementation does not support versions above "
+                    + FormatSpec.MAXIMUM_SUPPORTED_VERSION);
+        }
+        return version;
+    }
+
+    /**
+     * Reads a header from a buffer.
+     * @param buffer the buffer to read.
+     * @throws IOException
+     * @throws UnsupportedFormatException
+     */
+    public static FileHeader readHeader(final FusionDictionaryBufferInterface buffer)
+            throws IOException, UnsupportedFormatException {
+        final int version = checkFormatVersion(buffer);
+        final int optionsFlags = buffer.readUnsignedShort();
+
+        final HashMap<String, String> attributes = new HashMap<String, String>();
+        final int headerSize;
+        headerSize = buffer.readInt();
+
+        if (headerSize < 0) {
+            throw new UnsupportedFormatException("header size can't be negative.");
+        }
+
+        populateOptions(buffer, headerSize, attributes);
+        buffer.position(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 options from a buffer and populate a map with their contents.
+     *
+     * The buffer is read at the current position, so the caller must take care the pointer
+     * is in the right place before calling this.
+     */
+    public static void populateOptions(final FusionDictionaryBufferInterface buffer,
+            final int headerSize, final HashMap<String, String> options) {
+        while (buffer.position() < headerSize) {
+            final String key = CharEncoding.readString(buffer);
+            final String value = CharEncoding.readString(buffer);
+            options.put(key, value);
+        }
+    }
+
+    /**
+     * Reads a buffer and returns the memory representation of the dictionary.
+     *
+     * This high-level method takes a buffer and reads its contents, populating a
+     * FusionDictionary structure. The optional dict argument is an existing dictionary to
+     * which words from the buffer should be added. If it is null, a new dictionary is created.
+     *
+     * @param reader the reader.
+     * @param dict an optional dictionary to add words to, or null.
+     * @return the created (or merged) dictionary.
+     */
+    @UsedForTesting
+    public static FusionDictionary readDictionaryBinary(final BinaryDictReader reader,
+            final FusionDictionary dict) throws FileNotFoundException, IOException,
+            UnsupportedFormatException {
+        // clear cache
+        wordCache.clear();
+
+        // if the buffer has not been opened, open the buffer with bytebuffer.
+        if (reader.getBuffer() == null) reader.openBuffer(
+                new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
+        if (reader.getBuffer() == null) {
+            MakedictLog.e("Cannot open the buffer");
+        }
+
+        // Read header
+        final FileHeader header = readHeader(reader.getBuffer());
+
+        Map<Integer, Node> reverseNodeMapping = new TreeMap<Integer, Node>();
+        Map<Integer, CharGroup> reverseGroupMapping = new TreeMap<Integer, CharGroup>();
+        final Node root = readNode(reader.getBuffer(), header.mHeaderSize, reverseNodeMapping,
+                reverseGroupMapping, header.mFormatOptions);
+
+        FusionDictionary newDict = new FusionDictionary(root, header.mDictionaryOptions);
+        if (null != dict) {
+            for (final Word w : dict) {
+                if (w.mIsBlacklistEntry) {
+                    newDict.addBlacklistEntry(w.mWord, w.mShortcutTargets, w.mIsNotAWord);
+                } else {
+                    newDict.add(w.mWord, w.mFrequency, w.mShortcutTargets, w.mIsNotAWord);
+                }
+            }
+            for (final Word w : dict) {
+                // By construction a binary dictionary may not have bigrams pointing to
+                // words that are not also registered as unigrams so we don't have to avoid
+                // them explicitly here.
+                for (final WeightedString bigram : w.mBigrams) {
+                    newDict.setBigram(w.mWord, bigram.mWord, bigram.mFrequency);
+                }
+            }
+        }
+
+        return newDict;
+    }
+
+    /**
+     * Helper method to pass a file name instead of a File object to isBinaryDictionary.
+     */
+    public static boolean isBinaryDictionary(final String filename) {
+        final File file = new File(filename);
+        return isBinaryDictionary(file);
+    }
+
+    /**
+     * Basic test to find out whether the file is a binary dictionary or not.
+     *
+     * Concretely this only tests the magic number.
+     *
+     * @param file The file to test.
+     * @return true if it's a binary dictionary, false otherwise
+     */
+    public static boolean isBinaryDictionary(final File file) {
+        FileInputStream inStream = null;
+        try {
+            inStream = new FileInputStream(file);
+            final ByteBuffer buffer = inStream.getChannel().map(
+                    FileChannel.MapMode.READ_ONLY, 0, file.length());
+            final int version = getFormatVersion(new ByteBufferWrapper(buffer));
+            return (version >= FormatSpec.MINIMUM_SUPPORTED_VERSION
+                    && version <= FormatSpec.MAXIMUM_SUPPORTED_VERSION);
+        } catch (FileNotFoundException e) {
+            return false;
+        } catch (IOException e) {
+            return false;
+        } finally {
+            if (inStream != null) {
+                try {
+                    inStream.close();
+                } catch (IOException e) {
+                    // do nothing
+                }
+            }
+        }
+    }
+
+    /**
+     * Calculate bigram frequency from compressed value
+     *
+     * @see #makeBigramFlags
+     *
+     * @param unigramFrequency
+     * @param bigramFrequency compressed frequency
+     * @return approximate bigram frequency
+     */
+    public static int reconstructBigramFrequency(final int unigramFrequency,
+            final int bigramFrequency) {
+        final float stepSize = (FormatSpec.MAX_TERMINAL_FREQUENCY - unigramFrequency)
+                / (1.5f + FormatSpec.MAX_BIGRAM_FREQUENCY);
+        final float resultFreqFloat = unigramFrequency + stepSize * (bigramFrequency + 1.0f);
+        return (int)resultFreqFloat;
+    }
+}
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoder.java
index a33cddb49..85219e485 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoder.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2011 The Android Open Source Project
+ * 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.
@@ -16,275 +16,38 @@
 
 package com.android.inputmethod.latin.makedict;
 
-import com.android.inputmethod.annotations.UsedForTesting;
-import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.CharEncoding;
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
 import com.android.inputmethod.latin.makedict.FusionDictionary.DictionaryOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
-import com.android.inputmethod.latin.utils.JniUtils;
 
 import java.io.ByteArrayOutputStream;
-import java.io.File;
-import java.io.FileInputStream;
-import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.OutputStream;
-import java.nio.ByteBuffer;
-import java.nio.channels.FileChannel;
 import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.HashMap;
 import java.util.Iterator;
-import java.util.Map;
-import java.util.TreeMap;
 
 /**
- * Reads and writes XML files for a FusionDictionary.
+ * Encodes binary files for a FusionDictionary.
  *
  * All the methods in this class are static.
  */
-public final class BinaryDictInputOutput {
+public class BinaryDictEncoder {
 
     private static final boolean DBG = MakedictLog.DBG;
 
-    static {
-        JniUtils.loadNativeLibrary();
+    private BinaryDictEncoder() {
+        // This utility class is not publicly instantiable.
     }
 
-    // TODO: implement something sensical instead of just a phony method
-    private static native int doNothing();
-
     // Arbitrary limit to how much passes we consider address size compression should
     // terminate in. At the time of this writing, our largest dictionary completes
     // compression in five passes.
     // If the number of passes exceeds this number, makedict bails with an exception on
     // suspicion that a bug might be causing an infinite loop.
     private static final int MAX_PASSES = 24;
-    private static final int MAX_JUMPS = 12;
-
-    @UsedForTesting
-    public interface FusionDictionaryBufferInterface {
-        public int readUnsignedByte();
-        public int readUnsignedShort();
-        public int readUnsignedInt24();
-        public int readInt();
-        public int position();
-        public void position(int newPosition);
-        public void put(final byte b);
-        public int limit();
-        @UsedForTesting
-        public int capacity();
-    }
-
-    public static final class ByteBufferWrapper implements FusionDictionaryBufferInterface {
-        private ByteBuffer mBuffer;
-
-        public ByteBufferWrapper(final ByteBuffer buffer) {
-            mBuffer = buffer;
-        }
-
-        @Override
-        public int readUnsignedByte() {
-            return mBuffer.get() & 0xFF;
-        }
-
-        @Override
-        public int readUnsignedShort() {
-            return mBuffer.getShort() & 0xFFFF;
-        }
-
-        @Override
-        public int readUnsignedInt24() {
-            final int retval = readUnsignedByte();
-            return (retval << 16) + readUnsignedShort();
-        }
-
-        @Override
-        public int readInt() {
-            return mBuffer.getInt();
-        }
-
-        @Override
-        public int position() {
-            return mBuffer.position();
-        }
-
-        @Override
-        public void position(int newPos) {
-            mBuffer.position(newPos);
-        }
-
-        @Override
-        public void put(final byte b) {
-            mBuffer.put(b);
-        }
-
-        @Override
-        public int limit() {
-            return mBuffer.limit();
-        }
-
-        @Override
-        public int capacity() {
-            return mBuffer.capacity();
-        }
-    }
-
-    /**
-     * A class grouping utility function for our specific character encoding.
-     */
-    static final class CharEncoding {
-        private static final int MINIMAL_ONE_BYTE_CHARACTER_VALUE = 0x20;
-        private static final int MAXIMAL_ONE_BYTE_CHARACTER_VALUE = 0xFF;
-
-        /**
-         * Helper method to find out whether this code fits on one byte
-         */
-        private static boolean fitsOnOneByte(final int character) {
-            return character >= MINIMAL_ONE_BYTE_CHARACTER_VALUE
-                    && character <= MAXIMAL_ONE_BYTE_CHARACTER_VALUE;
-        }
-
-        /**
-         * Compute the size of a character given its character code.
-         *
-         * Char format is:
-         * 1 byte = bbbbbbbb match
-         * case 000xxxxx: xxxxx << 16 + next byte << 8 + next byte
-         * else: if 00011111 (= 0x1F) : this is the terminator. This is a relevant choice because
-         *       unicode code points range from 0 to 0x10FFFF, so any 3-byte value starting with
-         *       00011111 would be outside unicode.
-         * else: iso-latin-1 code
-         * This allows for the whole unicode range to be encoded, including chars outside of
-         * the BMP. Also everything in the iso-latin-1 charset is only 1 byte, except control
-         * characters which should never happen anyway (and still work, but take 3 bytes).
-         *
-         * @param character the character code.
-         * @return the size in binary encoded-form, either 1 or 3 bytes.
-         */
-        static int getCharSize(final int character) {
-            // See char encoding in FusionDictionary.java
-            if (fitsOnOneByte(character)) return 1;
-            if (FormatSpec.INVALID_CHARACTER == character) return 1;
-            return 3;
-        }
-
-        /**
-         * Compute the byte size of a character array.
-         */
-        private static int getCharArraySize(final int[] chars) {
-            int size = 0;
-            for (int character : chars) size += getCharSize(character);
-            return size;
-        }
-
-        /**
-         * Writes a char array to a byte buffer.
-         *
-         * @param codePoints the code point array to write.
-         * @param buffer the byte buffer to write to.
-         * @param index the index in buffer to write the character array to.
-         * @return the index after the last character.
-         */
-        private static int writeCharArray(final int[] codePoints, final byte[] buffer, int index) {
-            for (int codePoint : codePoints) {
-                if (1 == getCharSize(codePoint)) {
-                    buffer[index++] = (byte)codePoint;
-                } else {
-                    buffer[index++] = (byte)(0xFF & (codePoint >> 16));
-                    buffer[index++] = (byte)(0xFF & (codePoint >> 8));
-                    buffer[index++] = (byte)(0xFF & codePoint);
-                }
-            }
-            return index;
-        }
-
-        /**
-         * Writes a string with our character format to a byte buffer.
-         *
-         * This will also write the terminator byte.
-         *
-         * @param buffer the byte buffer to write to.
-         * @param origin the offset to write from.
-         * @param word the string to write.
-         * @return the size written, in bytes.
-         */
-        private static int writeString(final byte[] buffer, final int origin,
-                final String word) {
-            final int length = word.length();
-            int index = origin;
-            for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
-                final int codePoint = word.codePointAt(i);
-                if (1 == getCharSize(codePoint)) {
-                    buffer[index++] = (byte)codePoint;
-                } else {
-                    buffer[index++] = (byte)(0xFF & (codePoint >> 16));
-                    buffer[index++] = (byte)(0xFF & (codePoint >> 8));
-                    buffer[index++] = (byte)(0xFF & codePoint);
-                }
-            }
-            buffer[index++] = FormatSpec.GROUP_CHARACTERS_TERMINATOR;
-            return index - origin;
-        }
-
-        /**
-         * Writes a string with our character format to a ByteArrayOutputStream.
-         *
-         * This will also write the terminator byte.
-         *
-         * @param buffer the ByteArrayOutputStream to write to.
-         * @param word the string to write.
-         */
-        private static void writeString(final ByteArrayOutputStream buffer, final String word) {
-            final int length = word.length();
-            for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
-                final int codePoint = word.codePointAt(i);
-                if (1 == getCharSize(codePoint)) {
-                    buffer.write((byte) codePoint);
-                } else {
-                    buffer.write((byte) (0xFF & (codePoint >> 16)));
-                    buffer.write((byte) (0xFF & (codePoint >> 8)));
-                    buffer.write((byte) (0xFF & codePoint));
-                }
-            }
-            buffer.write(FormatSpec.GROUP_CHARACTERS_TERMINATOR);
-        }
-
-        /**
-         * Reads a string from a buffer. This is the converse of the above method.
-         */
-        private static String readString(final FusionDictionaryBufferInterface buffer) {
-            final StringBuilder s = new StringBuilder();
-            int character = readChar(buffer);
-            while (character != FormatSpec.INVALID_CHARACTER) {
-                s.appendCodePoint(character);
-                character = readChar(buffer);
-            }
-            return s.toString();
-        }
-
-        /**
-         * Reads a character from the buffer.
-         *
-         * This follows the character format documented earlier in this source file.
-         *
-         * @param buffer the buffer, positioned over an encoded character.
-         * @return the character code.
-         */
-        static int readChar(final FusionDictionaryBufferInterface buffer) {
-            int character = buffer.readUnsignedByte();
-            if (!fitsOnOneByte(character)) {
-                if (FormatSpec.GROUP_CHARACTERS_TERMINATOR == character) {
-                    return FormatSpec.INVALID_CHARACTER;
-                }
-                character <<= 16;
-                character += buffer.readUnsignedShort();
-            }
-            return character;
-        }
-    }
 
     /**
      * Compute the binary size of the character array.
@@ -432,7 +195,7 @@ public final class BinaryDictInputOutput {
         }
     }
 
-    // End utility methods.
+    // End utility methods
 
     // This method is responsible for finding a nice ordering of the nodes that favors run-time
     // cache performance and dictionary size.
@@ -1227,557 +990,4 @@ public final class BinaryDictInputOutput {
         destination.close();
         MakedictLog.i("Done");
     }
-
-
-    // Input methods: Read a binary dictionary to memory.
-    // readDictionaryBinary is the public entry point for them.
-
-    static int getChildrenAddressSize(final int optionFlags,
-            final FormatOptions formatOptions) {
-        if (formatOptions.mSupportsDynamicUpdate) return FormatSpec.SIGNED_CHILDREN_ADDRESS_SIZE;
-        switch (optionFlags & FormatSpec.MASK_GROUP_ADDRESS_TYPE) {
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
-                return 1;
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
-                return 2;
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
-                return 3;
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
-            default:
-                return 0;
-        }
-    }
-
-    static int readChildrenAddress(final FusionDictionaryBufferInterface buffer,
-            final int optionFlags, final FormatOptions options) {
-        if (options.mSupportsDynamicUpdate) {
-            final int address = buffer.readUnsignedInt24();
-            if (address == 0) return FormatSpec.NO_CHILDREN_ADDRESS;
-            if ((address & FormatSpec.MSB24) != 0) {
-                return -(address & FormatSpec.SINT24_MAX);
-            } else {
-                return address;
-            }
-        }
-        int address;
-        switch (optionFlags & FormatSpec.MASK_GROUP_ADDRESS_TYPE) {
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
-                return buffer.readUnsignedByte();
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
-                return buffer.readUnsignedShort();
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
-                return buffer.readUnsignedInt24();
-            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
-            default:
-                return FormatSpec.NO_CHILDREN_ADDRESS;
-        }
-    }
-
-    static int readParentAddress(final FusionDictionaryBufferInterface buffer,
-            final FormatOptions formatOptions) {
-        if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
-            final int parentAddress = buffer.readUnsignedInt24();
-            final int sign = ((parentAddress & FormatSpec.MSB24) != 0) ? -1 : 1;
-            return sign * (parentAddress & FormatSpec.SINT24_MAX);
-        } else {
-            return FormatSpec.NO_PARENT_ADDRESS;
-        }
-    }
-
-    private static final int[] CHARACTER_BUFFER = new int[FormatSpec.MAX_WORD_LENGTH];
-    public static CharGroupInfo readCharGroup(final FusionDictionaryBufferInterface buffer,
-            final int originalGroupAddress, final FormatOptions options) {
-        int addressPointer = originalGroupAddress;
-        final int flags = buffer.readUnsignedByte();
-        ++addressPointer;
-
-        final int parentAddress = readParentAddress(buffer, options);
-        if (BinaryDictIOUtils.supportsDynamicUpdate(options)) {
-            addressPointer += 3;
-        }
-
-        final int characters[];
-        if (0 != (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS)) {
-            int index = 0;
-            int character = CharEncoding.readChar(buffer);
-            addressPointer += CharEncoding.getCharSize(character);
-            while (-1 != 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 CHARACTER_BUFFER.
-                CHARACTER_BUFFER[index++] = character;
-                character = CharEncoding.readChar(buffer);
-                addressPointer += CharEncoding.getCharSize(character);
-            }
-            characters = Arrays.copyOfRange(CHARACTER_BUFFER, 0, index);
-        } else {
-            final int character = CharEncoding.readChar(buffer);
-            addressPointer += CharEncoding.getCharSize(character);
-            characters = new int[] { character };
-        }
-        final int frequency;
-        if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
-            ++addressPointer;
-            frequency = buffer.readUnsignedByte();
-        } else {
-            frequency = CharGroup.NOT_A_TERMINAL;
-        }
-        int childrenAddress = readChildrenAddress(buffer, flags, options);
-        if (childrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
-            childrenAddress += addressPointer;
-        }
-        addressPointer += getChildrenAddressSize(flags, options);
-        ArrayList<WeightedString> shortcutTargets = null;
-        if (0 != (flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS)) {
-            final int pointerBefore = buffer.position();
-            shortcutTargets = new ArrayList<WeightedString>();
-            buffer.readUnsignedShort(); // Skip the size
-            while (true) {
-                final int targetFlags = buffer.readUnsignedByte();
-                final String word = CharEncoding.readString(buffer);
-                shortcutTargets.add(new WeightedString(word,
-                        targetFlags & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY));
-                if (0 == (targetFlags & FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT)) break;
-            }
-            addressPointer += buffer.position() - pointerBefore;
-        }
-        ArrayList<PendingAttribute> bigrams = null;
-        if (0 != (flags & FormatSpec.FLAG_HAS_BIGRAMS)) {
-            bigrams = new ArrayList<PendingAttribute>();
-            int bigramCount = 0;
-            while (bigramCount++ < FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
-                final int bigramFlags = buffer.readUnsignedByte();
-                ++addressPointer;
-                final int sign = 0 == (bigramFlags & FormatSpec.FLAG_ATTRIBUTE_OFFSET_NEGATIVE)
-                        ? 1 : -1;
-                int bigramAddress = addressPointer;
-                switch (bigramFlags & FormatSpec.MASK_ATTRIBUTE_ADDRESS_TYPE) {
-                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
-                    bigramAddress += sign * buffer.readUnsignedByte();
-                    addressPointer += 1;
-                    break;
-                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
-                    bigramAddress += sign * buffer.readUnsignedShort();
-                    addressPointer += 2;
-                    break;
-                case FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
-                    final int offset = (buffer.readUnsignedByte() << 16)
-                            + buffer.readUnsignedShort();
-                    bigramAddress += sign * offset;
-                    addressPointer += 3;
-                    break;
-                default:
-                    throw new RuntimeException("Has bigrams with no address");
-                }
-                bigrams.add(new PendingAttribute(bigramFlags & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY,
-                        bigramAddress));
-                if (0 == (bigramFlags & FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT)) break;
-            }
-            if (bigramCount >= FormatSpec.MAX_BIGRAMS_IN_A_GROUP) {
-                MakedictLog.d("too many bigrams in a group.");
-            }
-        }
-        return new CharGroupInfo(originalGroupAddress, addressPointer, flags, characters, frequency,
-                parentAddress, childrenAddress, shortcutTargets, bigrams);
-    }
-
-    /**
-     * Reads and returns the char group count out of a buffer and forwards the pointer.
-     */
-    public static int readCharGroupCount(final FusionDictionaryBufferInterface buffer) {
-        final int msb = buffer.readUnsignedByte();
-        if (FormatSpec.MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT >= msb) {
-            return msb;
-        } else {
-            return ((FormatSpec.MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT & msb) << 8)
-                    + buffer.readUnsignedByte();
-        }
-    }
-
-    // The word cache here is a stopgap bandaid to help the catastrophic performance
-    // of this method. Since it performs direct, unbuffered random access to the file and
-    // may be called hundreds of thousands of times, the resulting performance is not
-    // reasonable without some kind of cache. Thus:
-    private static TreeMap<Integer, WeightedString> wordCache =
-            new TreeMap<Integer, WeightedString>();
-    /**
-     * Finds, as a string, the word at the address passed as an argument.
-     *
-     * @param buffer the buffer to read from.
-     * @param headerSize the size of the header.
-     * @param address the address to seek.
-     * @param formatOptions file format options.
-     * @return the word with its frequency, as a weighted string.
-     */
-    /* package for tests */ static WeightedString getWordAtAddress(
-            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
-            final FormatOptions formatOptions) {
-        final WeightedString cachedString = wordCache.get(address);
-        if (null != cachedString) return cachedString;
-
-        final WeightedString result;
-        final int originalPointer = buffer.position();
-        buffer.position(address);
-
-        if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
-            result = getWordAtAddressWithParentAddress(buffer, headerSize, address, formatOptions);
-        } else {
-            result = getWordAtAddressWithoutParentAddress(buffer, headerSize, address,
-                    formatOptions);
-        }
-
-        wordCache.put(address, result);
-        buffer.position(originalPointer);
-        return result;
-    }
-
-    // TODO: static!? This will behave erratically when used in multi-threaded code.
-    // We need to fix this
-    private static int[] sGetWordBuffer = new int[FormatSpec.MAX_WORD_LENGTH];
-    @SuppressWarnings("unused")
-    private static WeightedString getWordAtAddressWithParentAddress(
-            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
-            final FormatOptions options) {
-        int currentAddress = address;
-        int index = FormatSpec.MAX_WORD_LENGTH - 1;
-        int frequency = Integer.MIN_VALUE;
-        // the length of the path from the root to the leaf is limited by MAX_WORD_LENGTH
-        for (int count = 0; count < FormatSpec.MAX_WORD_LENGTH; ++count) {
-            CharGroupInfo currentInfo;
-            int loopCounter = 0;
-            do {
-                buffer.position(currentAddress + headerSize);
-                currentInfo = readCharGroup(buffer, currentAddress, options);
-                if (BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags, options)) {
-                    currentAddress = currentInfo.mParentAddress + currentInfo.mOriginalAddress;
-                }
-                if (DBG && loopCounter++ > MAX_JUMPS) {
-                    MakedictLog.d("Too many jumps - probably a bug");
-                }
-            } while (BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags, options));
-            if (Integer.MIN_VALUE == frequency) frequency = currentInfo.mFrequency;
-            for (int i = 0; i < currentInfo.mCharacters.length; ++i) {
-                sGetWordBuffer[index--] =
-                        currentInfo.mCharacters[currentInfo.mCharacters.length - i - 1];
-            }
-            if (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS) break;
-            currentAddress = currentInfo.mParentAddress + currentInfo.mOriginalAddress;
-        }
-
-        return new WeightedString(
-                new String(sGetWordBuffer, index + 1, FormatSpec.MAX_WORD_LENGTH - index - 1),
-                        frequency);
-    }
-
-    private static WeightedString getWordAtAddressWithoutParentAddress(
-            final FusionDictionaryBufferInterface buffer, final int headerSize, final int address,
-            final FormatOptions options) {
-        buffer.position(headerSize);
-        final int count = readCharGroupCount(buffer);
-        int groupOffset = BinaryDictIOUtils.getGroupCountSize(count);
-        final StringBuilder builder = new StringBuilder();
-        WeightedString result = null;
-
-        CharGroupInfo last = null;
-        for (int i = count - 1; i >= 0; --i) {
-            CharGroupInfo info = readCharGroup(buffer, groupOffset, options);
-            groupOffset = info.mEndAddress;
-            if (info.mOriginalAddress == address) {
-                builder.append(new String(info.mCharacters, 0, info.mCharacters.length));
-                result = new WeightedString(builder.toString(), info.mFrequency);
-                break; // and return
-            }
-            if (BinaryDictIOUtils.hasChildrenAddress(info.mChildrenAddress)) {
-                if (info.mChildrenAddress > address) {
-                    if (null == last) continue;
-                    builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
-                    buffer.position(last.mChildrenAddress + headerSize);
-                    i = readCharGroupCount(buffer);
-                    groupOffset = last.mChildrenAddress + BinaryDictIOUtils.getGroupCountSize(i);
-                    last = null;
-                    continue;
-                }
-                last = info;
-            }
-            if (0 == i && BinaryDictIOUtils.hasChildrenAddress(last.mChildrenAddress)) {
-                builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
-                buffer.position(last.mChildrenAddress + headerSize);
-                i = readCharGroupCount(buffer);
-                groupOffset = last.mChildrenAddress + BinaryDictIOUtils.getGroupCountSize(i);
-                last = null;
-                continue;
-            }
-        }
-        return result;
-    }
-
-    /**
-     * Reads a single node from a buffer.
-     *
-     * This methods reads the file at the current position. A node is fully expected to start at
-     * the current position.
-     * This will recursively read other nodes into the structure, populating the reverse
-     * maps on the fly and using them to keep track of already read nodes.
-     *
-     * @param buffer the buffer, correctly positioned at the start of a node.
-     * @param headerSize the size, in bytes, of the file header.
-     * @param reverseNodeMap a mapping from addresses to already read nodes.
-     * @param reverseGroupMap a mapping from addresses to already read character groups.
-     * @param options file format options.
-     * @return the read node with all his children already read.
-     */
-    private static Node readNode(final FusionDictionaryBufferInterface buffer, final int headerSize,
-            final Map<Integer, Node> reverseNodeMap, final Map<Integer, CharGroup> reverseGroupMap,
-            final FormatOptions options)
-            throws IOException {
-        final ArrayList<CharGroup> nodeContents = new ArrayList<CharGroup>();
-        final int nodeOrigin = buffer.position() - headerSize;
-
-        do { // Scan the linked-list node.
-            final int nodeHeadPosition = buffer.position() - headerSize;
-            final int count = readCharGroupCount(buffer);
-            int groupOffset = nodeHeadPosition + BinaryDictIOUtils.getGroupCountSize(count);
-            for (int i = count; i > 0; --i) { // Scan the array of CharGroup.
-                CharGroupInfo info = readCharGroup(buffer, groupOffset, options);
-                if (BinaryDictIOUtils.isMovedGroup(info.mFlags, options)) continue;
-                ArrayList<WeightedString> shortcutTargets = info.mShortcutTargets;
-                ArrayList<WeightedString> bigrams = null;
-                if (null != info.mBigrams) {
-                    bigrams = new ArrayList<WeightedString>();
-                    for (PendingAttribute bigram : info.mBigrams) {
-                        final WeightedString word = getWordAtAddress(
-                                buffer, headerSize, bigram.mAddress, options);
-                        final int reconstructedFrequency =
-                                reconstructBigramFrequency(word.mFrequency, bigram.mFrequency);
-                        bigrams.add(new WeightedString(word.mWord, reconstructedFrequency));
-                    }
-                }
-                if (BinaryDictIOUtils.hasChildrenAddress(info.mChildrenAddress)) {
-                    Node children = reverseNodeMap.get(info.mChildrenAddress);
-                    if (null == children) {
-                        final int currentPosition = buffer.position();
-                        buffer.position(info.mChildrenAddress + headerSize);
-                        children = readNode(
-                                buffer, headerSize, reverseNodeMap, reverseGroupMap, options);
-                        buffer.position(currentPosition);
-                    }
-                    nodeContents.add(
-                            new CharGroup(info.mCharacters, shortcutTargets, bigrams,
-                                    info.mFrequency,
-                                    0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
-                                    0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED), children));
-                } else {
-                    nodeContents.add(
-                            new CharGroup(info.mCharacters, shortcutTargets, bigrams,
-                                    info.mFrequency,
-                                    0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
-                                    0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED)));
-                }
-                groupOffset = info.mEndAddress;
-            }
-
-            // reach the end of the array.
-            if (options.mSupportsDynamicUpdate) {
-                final int nextAddress = buffer.readUnsignedInt24();
-                if (nextAddress >= 0 && nextAddress < buffer.limit()) {
-                    buffer.position(nextAddress);
-                } else {
-                    break;
-                }
-            }
-        } while (options.mSupportsDynamicUpdate &&
-                buffer.position() != FormatSpec.NO_FORWARD_LINK_ADDRESS);
-
-        final Node node = new Node(nodeContents);
-        node.mCachedAddressBeforeUpdate = nodeOrigin;
-        node.mCachedAddressAfterUpdate = nodeOrigin;
-        reverseNodeMap.put(node.mCachedAddressAfterUpdate, node);
-        return node;
-    }
-
-    /**
-     * Helper function to get the binary format version from the header.
-     * @throws IOException
-     */
-    private static int getFormatVersion(final FusionDictionaryBufferInterface buffer)
-            throws IOException {
-        final int magic = buffer.readInt();
-        if (FormatSpec.MAGIC_NUMBER == magic) return buffer.readUnsignedShort();
-        return FormatSpec.NOT_A_VERSION_NUMBER;
-    }
-
-    /**
-     * Helper function to get and validate the binary format version.
-     * @throws UnsupportedFormatException
-     * @throws IOException
-     */
-    private static int checkFormatVersion(final FusionDictionaryBufferInterface buffer)
-            throws IOException, UnsupportedFormatException {
-        final int version = getFormatVersion(buffer);
-        if (version < FormatSpec.MINIMUM_SUPPORTED_VERSION
-                || version > FormatSpec.MAXIMUM_SUPPORTED_VERSION) {
-            throw new UnsupportedFormatException("This file has version " + version
-                    + ", but this implementation does not support versions above "
-                    + FormatSpec.MAXIMUM_SUPPORTED_VERSION);
-        }
-        return version;
-    }
-
-    /**
-     * Reads a header from a buffer.
-     * @param buffer the buffer to read.
-     * @throws IOException
-     * @throws UnsupportedFormatException
-     */
-    public static FileHeader readHeader(final FusionDictionaryBufferInterface buffer)
-            throws IOException, UnsupportedFormatException {
-        final int version = checkFormatVersion(buffer);
-        final int optionsFlags = buffer.readUnsignedShort();
-
-        final HashMap<String, String> attributes = new HashMap<String, String>();
-        final int headerSize;
-        headerSize = buffer.readInt();
-
-        if (headerSize < 0) {
-            throw new UnsupportedFormatException("header size can't be negative.");
-        }
-
-        populateOptions(buffer, headerSize, attributes);
-        buffer.position(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 options from a buffer and populate a map with their contents.
-     *
-     * The buffer is read at the current position, so the caller must take care the pointer
-     * is in the right place before calling this.
-     */
-    public static void populateOptions(final FusionDictionaryBufferInterface buffer,
-            final int headerSize, final HashMap<String, String> options) {
-        while (buffer.position() < headerSize) {
-            final String key = CharEncoding.readString(buffer);
-            final String value = CharEncoding.readString(buffer);
-            options.put(key, value);
-        }
-    }
-
-    /**
-     * Reads a buffer and returns the memory representation of the dictionary.
-     *
-     * This high-level method takes a buffer and reads its contents, populating a
-     * FusionDictionary structure. The optional dict argument is an existing dictionary to
-     * which words from the buffer should be added. If it is null, a new dictionary is created.
-     *
-     * @param reader the reader.
-     * @param dict an optional dictionary to add words to, or null.
-     * @return the created (or merged) dictionary.
-     */
-    @UsedForTesting
-    public static FusionDictionary readDictionaryBinary(final BinaryDictReader reader,
-            final FusionDictionary dict) throws FileNotFoundException, IOException,
-            UnsupportedFormatException {
-        // clear cache
-        wordCache.clear();
-
-        // if the buffer has not been opened, open the buffer with bytebuffer.
-        if (reader.getBuffer() == null) reader.openBuffer(
-                new BinaryDictReader.FusionDictionaryBufferFromByteBufferFactory());
-        if (reader.getBuffer() == null) {
-            MakedictLog.e("Cannot open the buffer");
-        }
-
-        // Read header
-        final FileHeader header = readHeader(reader.getBuffer());
-
-        Map<Integer, Node> reverseNodeMapping = new TreeMap<Integer, Node>();
-        Map<Integer, CharGroup> reverseGroupMapping = new TreeMap<Integer, CharGroup>();
-        final Node root = readNode(reader.getBuffer(), header.mHeaderSize, reverseNodeMapping,
-                reverseGroupMapping, header.mFormatOptions);
-
-        FusionDictionary newDict = new FusionDictionary(root, header.mDictionaryOptions);
-        if (null != dict) {
-            for (final Word w : dict) {
-                if (w.mIsBlacklistEntry) {
-                    newDict.addBlacklistEntry(w.mWord, w.mShortcutTargets, w.mIsNotAWord);
-                } else {
-                    newDict.add(w.mWord, w.mFrequency, w.mShortcutTargets, w.mIsNotAWord);
-                }
-            }
-            for (final Word w : dict) {
-                // By construction a binary dictionary may not have bigrams pointing to
-                // words that are not also registered as unigrams so we don't have to avoid
-                // them explicitly here.
-                for (final WeightedString bigram : w.mBigrams) {
-                    newDict.setBigram(w.mWord, bigram.mWord, bigram.mFrequency);
-                }
-            }
-        }
-
-        return newDict;
-    }
-
-    /**
-     * Helper method to pass a file name instead of a File object to isBinaryDictionary.
-     */
-    public static boolean isBinaryDictionary(final String filename) {
-        final File file = new File(filename);
-        return isBinaryDictionary(file);
-    }
-
-    /**
-     * Basic test to find out whether the file is a binary dictionary or not.
-     *
-     * Concretely this only tests the magic number.
-     *
-     * @param file The file to test.
-     * @return true if it's a binary dictionary, false otherwise
-     */
-    public static boolean isBinaryDictionary(final File file) {
-        FileInputStream inStream = null;
-        try {
-            inStream = new FileInputStream(file);
-            final ByteBuffer buffer = inStream.getChannel().map(
-                    FileChannel.MapMode.READ_ONLY, 0, file.length());
-            final int version = getFormatVersion(new ByteBufferWrapper(buffer));
-            return (version >= FormatSpec.MINIMUM_SUPPORTED_VERSION
-                    && version <= FormatSpec.MAXIMUM_SUPPORTED_VERSION);
-        } catch (FileNotFoundException e) {
-            return false;
-        } catch (IOException e) {
-            return false;
-        } finally {
-            if (inStream != null) {
-                try {
-                    inStream.close();
-                } catch (IOException e) {
-                    // do nothing
-                }
-            }
-        }
-    }
-
-    /**
-     * Calculate bigram frequency from compressed value
-     *
-     * @see #makeBigramFlags
-     *
-     * @param unigramFrequency
-     * @param bigramFrequency compressed frequency
-     * @return approximate bigram frequency
-     */
-    public static int reconstructBigramFrequency(final int unigramFrequency,
-            final int bigramFrequency) {
-        final float stepSize = (FormatSpec.MAX_TERMINAL_FREQUENCY - unigramFrequency)
-                / (1.5f + FormatSpec.MAX_BIGRAM_FREQUENCY);
-        final float resultFreqFloat = unigramFrequency + stepSize * (bigramFrequency + 1.0f);
-        return (int)resultFreqFloat;
-    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
index 2e6c4b2f8..c013013e6 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
@@ -18,8 +18,8 @@ package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.Constants;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.CharEncoding;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.CharEncoding;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.FusionDictionaryBufferInterface;
 import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary.CharGroup;
@@ -86,7 +86,7 @@ public final class BinaryDictIOUtils {
             if (index != p.mLength) index = p.mLength;
 
             if (p.mNumOfCharGroup == Position.NOT_READ_GROUPCOUNT) {
-                p.mNumOfCharGroup = BinaryDictInputOutput.readCharGroupCount(buffer);
+                p.mNumOfCharGroup = BinaryDictDecoder.readCharGroupCount(buffer);
                 p.mAddress += getGroupCountSize(p.mNumOfCharGroup);
                 p.mPosition = 0;
             }
@@ -94,7 +94,7 @@ public final class BinaryDictIOUtils {
                 stack.pop();
                 continue;
             }
-            CharGroupInfo info = BinaryDictInputOutput.readCharGroup(buffer,
+            CharGroupInfo info = BinaryDictDecoder.readCharGroup(buffer,
                     p.mAddress - headerSize, formatOptions);
             for (int i = 0; i < info.mCharacters.length; ++i) {
                 pushedChars[index++] = info.mCharacters[i];
@@ -153,7 +153,7 @@ public final class BinaryDictIOUtils {
             final Map<Integer, ArrayList<PendingAttribute>> bigrams) throws IOException,
             UnsupportedFormatException {
         // Read header
-        final FileHeader header = BinaryDictInputOutput.readHeader(reader.getBuffer());
+        final FileHeader header = BinaryDictDecoder.readHeader(reader.getBuffer());
         readUnigramsAndBigramsBinaryInner(reader.getBuffer(), header.mHeaderSize, words,
                 frequencies, bigrams, header.mFormatOptions);
     }
@@ -174,18 +174,18 @@ public final class BinaryDictIOUtils {
         if (word == null) return FormatSpec.NOT_VALID_WORD;
         if (buffer.position() != 0) buffer.position(0);
 
-        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
         int wordPos = 0;
         final int wordLen = word.codePointCount(0, word.length());
         for (int depth = 0; depth < Constants.DICTIONARY_MAX_WORD_LENGTH; ++depth) {
             if (wordPos >= wordLen) return FormatSpec.NOT_VALID_WORD;
 
             do {
-                final int charGroupCount = BinaryDictInputOutput.readCharGroupCount(buffer);
+                final int charGroupCount = BinaryDictDecoder.readCharGroupCount(buffer);
                 boolean foundNextCharGroup = false;
                 for (int i = 0; i < charGroupCount; ++i) {
                     final int charGroupPos = buffer.position();
-                    final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
+                    final CharGroupInfo currentInfo = BinaryDictDecoder.readCharGroup(buffer,
                             buffer.position(), header.mFormatOptions);
                     final boolean isMovedGroup = isMovedGroup(currentInfo.mFlags,
                             header.mFormatOptions);
@@ -271,7 +271,7 @@ public final class BinaryDictIOUtils {
      */
     private static int writeVariableAddress(final OutputStream destination, final int value)
             throws IOException {
-        switch (BinaryDictInputOutput.getByteSize(value)) {
+        switch (BinaryDictEncoder.getByteSize(value)) {
         case 1:
             destination.write((byte)value);
             break;
@@ -285,15 +285,15 @@ public final class BinaryDictIOUtils {
             destination.write((byte)(0xFF & value));
             break;
         }
-        return BinaryDictInputOutput.getByteSize(value);
+        return BinaryDictEncoder.getByteSize(value);
     }
 
     static void skipCharGroup(final FusionDictionaryBufferInterface buffer,
             final FormatOptions formatOptions) {
         final int flags = buffer.readUnsignedByte();
-        BinaryDictInputOutput.readParentAddress(buffer, formatOptions);
+        BinaryDictDecoder.readParentAddress(buffer, formatOptions);
         skipString(buffer, (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS) != 0);
-        BinaryDictInputOutput.readChildrenAddress(buffer, flags, formatOptions);
+        BinaryDictDecoder.readChildrenAddress(buffer, flags, formatOptions);
         if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) buffer.readUnsignedByte();
         if ((flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS) != 0) {
             final int shortcutsSize = buffer.readUnsignedShort();
@@ -411,14 +411,14 @@ public final class BinaryDictIOUtils {
 
         if (info.mShortcutTargets != null && info.mShortcutTargets.size() > 0) {
             final int shortcutListSize =
-                    BinaryDictInputOutput.getShortcutListSize(info.mShortcutTargets);
+                    BinaryDictEncoder.getShortcutListSize(info.mShortcutTargets);
             destination.write((byte)(shortcutListSize >> 8));
             destination.write((byte)(shortcutListSize & 0xFF));
             size += 2;
             final Iterator<WeightedString> shortcutIterator = info.mShortcutTargets.iterator();
             while (shortcutIterator.hasNext()) {
                 final WeightedString target = shortcutIterator.next();
-                destination.write((byte)BinaryDictInputOutput.makeShortcutFlags(
+                destination.write((byte)BinaryDictEncoder.makeShortcutFlags(
                         shortcutIterator.hasNext(), target.mFrequency));
                 size++;
                 size += writeString(destination, target.mWord);
@@ -427,7 +427,7 @@ public final class BinaryDictIOUtils {
 
         if (info.mBigrams != null) {
             // TODO: Consolidate this code with the code that computes the size of the bigram list
-            //        in BinaryDictionaryInputOutput#computeActualNodeSize
+            //        in BinaryDictEncoder#computeActualNodeSize
             for (int i = 0; i < info.mBigrams.size(); ++i) {
 
                 final int bigramFrequency = info.mBigrams.get(i).mFrequency;
@@ -437,7 +437,7 @@ public final class BinaryDictIOUtils {
                 final int bigramOffset = info.mBigrams.get(i).mAddress - (info.mOriginalAddress
                         + size);
                 bigramFlags |= (bigramOffset < 0) ? FormatSpec.FLAG_ATTRIBUTE_OFFSET_NEGATIVE : 0;
-                switch (BinaryDictInputOutput.getByteSize(bigramOffset)) {
+                switch (BinaryDictEncoder.getByteSize(bigramOffset)) {
                 case 1:
                     bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE;
                     break;
@@ -461,18 +461,18 @@ public final class BinaryDictIOUtils {
      */
     static int computeGroupSize(final CharGroupInfo info, final FormatOptions formatOptions) {
         int size = FormatSpec.GROUP_FLAGS_SIZE + FormatSpec.PARENT_ADDRESS_SIZE
-                + BinaryDictInputOutput.getGroupCharactersSize(info.mCharacters)
-                + BinaryDictInputOutput.getChildrenAddressSize(info.mFlags, formatOptions);
+                + BinaryDictEncoder.getGroupCharactersSize(info.mCharacters)
+                + getChildrenAddressSize(info.mFlags, formatOptions);
         if ((info.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0) {
             size += FormatSpec.GROUP_FREQUENCY_SIZE;
         }
         if (info.mShortcutTargets != null && !info.mShortcutTargets.isEmpty()) {
-            size += BinaryDictInputOutput.getShortcutListSize(info.mShortcutTargets);
+            size += BinaryDictEncoder.getShortcutListSize(info.mShortcutTargets);
         }
         if (info.mBigrams != null) {
             for (final PendingAttribute attr : info.mBigrams) {
                 size += FormatSpec.GROUP_FLAGS_SIZE;
-                size += BinaryDictInputOutput.getByteSize(attr.mAddress);
+                size += BinaryDictEncoder.getByteSize(attr.mAddress);
             }
         }
         return size;
@@ -520,9 +520,9 @@ public final class BinaryDictIOUtils {
         int position = getTerminalPosition(buffer, word);
         if (position != FormatSpec.NOT_VALID_WORD) {
             buffer.position(0);
-            final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+            final FileHeader header = BinaryDictDecoder.readHeader(buffer);
             buffer.position(position);
-            return BinaryDictInputOutput.readCharGroup(buffer, position, header.mFormatOptions);
+            return BinaryDictDecoder.readCharGroup(buffer, position, header.mFormatOptions);
         }
         return null;
     }
@@ -544,10 +544,10 @@ public final class BinaryDictIOUtils {
         final FileInputStream inStream = new FileInputStream(file);
         try {
             inStream.read(buffer);
-            final BinaryDictInputOutput.ByteBufferWrapper wrapper =
-                    new BinaryDictInputOutput.ByteBufferWrapper(inStream.getChannel().map(
+            final BinaryDictDecoder.ByteBufferWrapper wrapper =
+                    new BinaryDictDecoder.ByteBufferWrapper(inStream.getChannel().map(
                             FileChannel.MapMode.READ_ONLY, offset, length));
-            return BinaryDictInputOutput.readHeader(wrapper);
+            return BinaryDictDecoder.readHeader(wrapper);
         } finally {
             inStream.close();
         }
@@ -612,4 +612,20 @@ public final class BinaryDictIOUtils {
                     + ")");
         }
     }
+
+    static int getChildrenAddressSize(final int optionFlags,
+            final FormatOptions formatOptions) {
+        if (formatOptions.mSupportsDynamicUpdate) return FormatSpec.SIGNED_CHILDREN_ADDRESS_SIZE;
+        switch (optionFlags & FormatSpec.MASK_GROUP_ADDRESS_TYPE) {
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
+                return 1;
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
+                return 2;
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
+                return 3;
+            case FormatSpec.FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
+            default:
+                return 0;
+        }
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
index a4a7ce458..f2f3c465d 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictReader.java
@@ -17,7 +17,7 @@
 package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.annotations.UsedForTesting;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.FusionDictionaryBufferInterface;
 import com.android.inputmethod.latin.utils.ByteArrayWrapper;
 
 import java.io.File;
@@ -55,7 +55,7 @@ public class BinaryDictReader {
                 }
             }
             if (buffer != null) {
-                return new BinaryDictInputOutput.ByteBufferWrapper(buffer);
+                return new BinaryDictDecoder.ByteBufferWrapper(buffer);
             }
             return null;
         }
@@ -103,7 +103,7 @@ public class BinaryDictReader {
                 }
             }
             if (buffer != null) {
-                return new BinaryDictInputOutput.ByteBufferWrapper(buffer);
+                return new BinaryDictDecoder.ByteBufferWrapper(buffer);
             }
             return null;
         }
diff --git a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
index 5b10912ea..4dbfcb77d 100644
--- a/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/DynamicBinaryDictIOUtils.java
@@ -18,7 +18,7 @@ package com.android.inputmethod.latin.makedict;
 
 import com.android.inputmethod.annotations.UsedForTesting;
 import com.android.inputmethod.latin.Constants;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.FusionDictionaryBufferInterface;
 import com.android.inputmethod.latin.makedict.FormatSpec.FileHeader;
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
@@ -58,7 +58,7 @@ public final class DynamicBinaryDictIOUtils {
     public static void deleteWord(final FusionDictionaryBufferInterface buffer,
             final String word) throws IOException, UnsupportedFormatException {
         buffer.position(0);
-        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
         final int wordPosition = BinaryDictIOUtils.getTerminalPosition(buffer, word);
         if (wordPosition == FormatSpec.NOT_VALID_WORD) return;
 
@@ -114,7 +114,7 @@ public final class DynamicBinaryDictIOUtils {
         final int originalPosition = buffer.position();
         buffer.position(nodeOriginAddress);
         do {
-            final int count = BinaryDictInputOutput.readCharGroupCount(buffer);
+            final int count = BinaryDictDecoder.readCharGroupCount(buffer);
             for (int i = 0; i < count; ++i) {
                 updateParentAddress(buffer, buffer.position(), newParentAddress, formatOptions);
                 BinaryDictIOUtils.skipCharGroup(buffer, formatOptions);
@@ -140,7 +140,7 @@ public final class DynamicBinaryDictIOUtils {
         final int originalPosition = buffer.position();
         buffer.position(groupOriginAddress);
         final int flags = buffer.readUnsignedByte();
-        final int parentAddress = BinaryDictInputOutput.readParentAddress(buffer, formatOptions);
+        final int parentAddress = BinaryDictDecoder.readParentAddress(buffer, formatOptions);
         BinaryDictIOUtils.skipString(buffer, (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS) != 0);
         if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) buffer.readUnsignedByte();
         final int childrenOffset = newChildrenAddress == FormatSpec.NO_CHILDREN_ADDRESS
@@ -174,7 +174,7 @@ public final class DynamicBinaryDictIOUtils {
         buffer.position(nodeOriginAddress);
         int jumpCount = 0;
         while (jumpCount++ < MAX_JUMPS) {
-            final int count = BinaryDictInputOutput.readCharGroupCount(buffer);
+            final int count = BinaryDictDecoder.readCharGroupCount(buffer);
             for (int i = 0; i < count; ++i) BinaryDictIOUtils.skipCharGroup(buffer, formatOptions);
             final int forwardLinkAddress = buffer.readUnsignedInt24();
             if (forwardLinkAddress == FormatSpec.NO_FORWARD_LINK_ADDRESS) {
@@ -269,7 +269,7 @@ public final class DynamicBinaryDictIOUtils {
 
         // find the insert position of the word.
         if (buffer.position() != 0) buffer.position(0);
-        final FileHeader header = BinaryDictInputOutput.readHeader(buffer);
+        final FileHeader header = BinaryDictDecoder.readHeader(buffer);
 
         int wordPos = 0, address = buffer.position(), nodeOriginAddress = buffer.position();
         final int[] codePoints = FusionDictionary.getCodePoints(word);
@@ -279,12 +279,12 @@ public final class DynamicBinaryDictIOUtils {
             if (wordPos >= wordLen) break;
             nodeOriginAddress = buffer.position();
             int nodeParentAddress = -1;
-            final int charGroupCount = BinaryDictInputOutput.readCharGroupCount(buffer);
+            final int charGroupCount = BinaryDictDecoder.readCharGroupCount(buffer);
             boolean foundNextGroup = false;
 
             for (int i = 0; i < charGroupCount; ++i) {
                 address = buffer.position();
-                final CharGroupInfo currentInfo = BinaryDictInputOutput.readCharGroup(buffer,
+                final CharGroupInfo currentInfo = BinaryDictDecoder.readCharGroup(buffer,
                         buffer.position(), header.mFormatOptions);
                 final boolean isMovedGroup = BinaryDictIOUtils.isMovedGroup(currentInfo.mFlags,
                         header.mFormatOptions);
@@ -305,7 +305,7 @@ public final class DynamicBinaryDictIOUtils {
                          *  abc - d - ef
                          */
                         final int newNodeAddress = buffer.limit();
-                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
+                        final int flags = BinaryDictEncoder.makeCharGroupFlags(p > 1,
                                 isTerminal, 0, hasShortcuts, hasBigrams, false /* isNotAWord */,
                                 false /* isBlackListEntry */, header.mFormatOptions);
                         int written = moveGroup(newNodeAddress, currentInfo.mCharacters, p, flags,
@@ -344,7 +344,7 @@ public final class DynamicBinaryDictIOUtils {
                             final int childrenAddress = currentInfo.mChildrenAddress;
 
                             // move prefix
-                            final int prefixFlags = BinaryDictInputOutput.makeCharGroupFlags(p > 1,
+                            final int prefixFlags = BinaryDictEncoder.makeCharGroupFlags(p > 1,
                                     false /* isTerminal */, 0 /* childrenAddressSize*/,
                                     false /* hasShortcut */, false /* hasBigrams */,
                                     false /* isNotAWord */, false /* isBlackListEntry */,
@@ -360,7 +360,7 @@ public final class DynamicBinaryDictIOUtils {
                                 updateParentAddresses(buffer, currentInfo.mChildrenAddress,
                                         newNodeAddress + written + 1, header.mFormatOptions);
                             }
-                            final int suffixFlags = BinaryDictInputOutput.makeCharGroupFlags(
+                            final int suffixFlags = BinaryDictEncoder.makeCharGroupFlags(
                                     suffixCharacters.length > 1,
                                     (currentInfo.mFlags & FormatSpec.FLAG_IS_TERMINAL) != 0,
                                     0 /* childrenAddressSize */,
@@ -378,7 +378,7 @@ public final class DynamicBinaryDictIOUtils {
 
                             final int[] newCharacters = Arrays.copyOfRange(codePoints, wordPos + p,
                                     codePoints.length);
-                            final int flags = BinaryDictInputOutput.makeCharGroupFlags(
+                            final int flags = BinaryDictEncoder.makeCharGroupFlags(
                                     newCharacters.length > 1, isTerminal,
                                     0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                     isNotAWord, isBlackListEntry, header.mFormatOptions);
@@ -401,7 +401,7 @@ public final class DynamicBinaryDictIOUtils {
                         // only update group.
                         final int newNodeAddress = buffer.limit();
                         final boolean hasMultipleChars = currentInfo.mCharacters.length > 1;
-                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
+                        final int flags = BinaryDictEncoder.makeCharGroupFlags(hasMultipleChars,
                                 isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                 isNotAWord, isBlackListEntry, header.mFormatOptions);
                         final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
@@ -431,7 +431,7 @@ public final class DynamicBinaryDictIOUtils {
                                 header.mFormatOptions);
                         final int newGroupAddress = newNodeAddress + 1;
                         final boolean hasMultipleChars = (wordLen - wordPos) > 1;
-                        final int flags = BinaryDictInputOutput.makeCharGroupFlags(hasMultipleChars,
+                        final int flags = BinaryDictEncoder.makeCharGroupFlags(hasMultipleChars,
                                 isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                                 isNotAWord, isBlackListEntry, header.mFormatOptions);
                         final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
@@ -476,7 +476,7 @@ public final class DynamicBinaryDictIOUtils {
                 BinaryDictIOUtils.writeSInt24ToBuffer(buffer, newNodeAddress);
 
                 final int[] characters = Arrays.copyOfRange(codePoints, wordPos, wordLen);
-                final int flags = BinaryDictInputOutput.makeCharGroupFlags(characters.length > 1,
+                final int flags = BinaryDictEncoder.makeCharGroupFlags(characters.length > 1,
                         isTerminal, 0 /* childrenAddressSize */, hasShortcuts, hasBigrams,
                         isNotAWord, isBlackListEntry, header.mFormatOptions);
                 final CharGroupInfo newInfo = new CharGroupInfo(newNodeAddress + 1,
diff --git a/java/src/com/android/inputmethod/latin/utils/ByteArrayWrapper.java b/java/src/com/android/inputmethod/latin/utils/ByteArrayWrapper.java
index 1bb27aa2b..d93b61451 100644
--- a/java/src/com/android/inputmethod/latin/utils/ByteArrayWrapper.java
+++ b/java/src/com/android/inputmethod/latin/utils/ByteArrayWrapper.java
@@ -16,7 +16,7 @@
 
 package com.android.inputmethod.latin.utils;
 
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput.FusionDictionaryBufferInterface;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder.FusionDictionaryBufferInterface;
 
 /**
  * This class provides an implementation for the FusionDictionary buffer interface that is backed
diff --git a/java/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtils.java b/java/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtils.java
index a0ad27cfb..aed07fd16 100644
--- a/java/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/utils/UserHistoryDictIOUtils.java
@@ -19,8 +19,9 @@ package com.android.inputmethod.latin.utils;
 import android.util.Log;
 
 import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoder;
+import com.android.inputmethod.latin.makedict.BinaryDictEncoder;
 import com.android.inputmethod.latin.makedict.BinaryDictIOUtils;
-import com.android.inputmethod.latin.makedict.BinaryDictInputOutput;
 import com.android.inputmethod.latin.makedict.BinaryDictReader;
 import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
 import com.android.inputmethod.latin.makedict.FusionDictionary;
@@ -62,7 +63,7 @@ public final class UserHistoryDictIOUtils {
             final FormatOptions formatOptions) {
         final FusionDictionary fusionDict = constructFusionDictionary(dict, bigrams);
         try {
-            BinaryDictInputOutput.writeDictionaryBinary(destination, fusionDict, formatOptions);
+            BinaryDictEncoder.writeDictionaryBinary(destination, fusionDict, formatOptions);
             Log.d(TAG, "end writing");
         } catch (IOException e) {
             Log.e(TAG, "IO exception while writing file", e);
@@ -156,7 +157,7 @@ public final class UserHistoryDictIOUtils {
                         continue;
                     }
                     to.setBigram(word1, word2,
-                            BinaryDictInputOutput.reconstructBigramFrequency(unigramFrequency,
+                            BinaryDictDecoder.reconstructBigramFrequency(unigramFrequency,
                                     attr.mFrequency));
                 }
             }