Revert "[Refactor] Divide BinaryDictInputOutput into BinaryDictInputUtils and BinaryDictOutputUtils."

This reverts commit 4c63d0614e7ed7aea4bcbab3a17090d841661d92.

Change-Id: I1fa277d720bab4d895259df7d6d82eebfa5eb6c5

1 files changed, 1775 insertions, 0 deletions

diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
new file mode 100644
index 000000000..a54661058
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -0,0 +1,1775 @@
+/*
+ * Copyright (C) 2011 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.DictionaryOptions;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+
+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.
+ *
+ * All the methods in this class are static.
+ */
+public final class BinaryDictInputOutput {
+
+    private static final boolean DBG = MakedictLog.DBG;
+
+    // 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.
+     *
+     * If only one character, this is the size of this character. If many, it's the sum of their
+     * sizes + 1 byte for the terminator.
+     *
+     * @param characters the character array
+     * @return the size of the char array, including the terminator if any
+     */
+    static int getGroupCharactersSize(final int[] characters) {
+        int size = CharEncoding.getCharArraySize(characters);
+        if (characters.length > 1) size += FormatSpec.GROUP_TERMINATOR_SIZE;
+        return size;
+    }
+
+    /**
+     * Compute the binary size of the character array in a group
+     *
+     * If only one character, this is the size of this character. If many, it's the sum of their
+     * sizes + 1 byte for the terminator.
+     *
+     * @param group the group
+     * @return the size of the char array, including the terminator if any
+     */
+    private static int getGroupCharactersSize(final CharGroup group) {
+        return getGroupCharactersSize(group.mChars);
+    }
+
+    /**
+     * Compute the binary size of the group count for a node
+     * @param node the node
+     * @return the size of the group count, either 1 or 2 bytes.
+     */
+    private static int getGroupCountSize(final Node node) {
+        return BinaryDictIOUtils.getGroupCountSize(node.mData.size());
+    }
+
+    /**
+     * Compute the size of a shortcut in bytes.
+     */
+    private static int getShortcutSize(final WeightedString shortcut) {
+        int size = FormatSpec.GROUP_ATTRIBUTE_FLAGS_SIZE;
+        final String word = shortcut.mWord;
+        final int length = word.length();
+        for (int i = 0; i < length; i = word.offsetByCodePoints(i, 1)) {
+            final int codePoint = word.codePointAt(i);
+            size += CharEncoding.getCharSize(codePoint);
+        }
+        size += FormatSpec.GROUP_TERMINATOR_SIZE;
+        return size;
+    }
+
+    /**
+     * Compute the size of a shortcut list in bytes.
+     *
+     * This is known in advance and does not change according to position in the file
+     * like address lists do.
+     */
+    static int getShortcutListSize(final ArrayList<WeightedString> shortcutList) {
+        if (null == shortcutList) return 0;
+        int size = FormatSpec.GROUP_SHORTCUT_LIST_SIZE_SIZE;
+        for (final WeightedString shortcut : shortcutList) {
+            size += getShortcutSize(shortcut);
+        }
+        return size;
+    }
+
+    /**
+     * Compute the maximum size of a CharGroup, assuming 3-byte addresses for everything.
+     *
+     * @param group the CharGroup to compute the size of.
+     * @param options file format options.
+     * @return the maximum size of the group.
+     */
+    private static int getCharGroupMaximumSize(final CharGroup group, final FormatOptions options) {
+        int size = getGroupHeaderSize(group, options);
+        // If terminal, one byte for the frequency
+        if (group.isTerminal()) size += FormatSpec.GROUP_FREQUENCY_SIZE;
+        size += FormatSpec.GROUP_MAX_ADDRESS_SIZE; // For children address
+        size += getShortcutListSize(group.mShortcutTargets);
+        if (null != group.mBigrams) {
+            size += (FormatSpec.GROUP_ATTRIBUTE_FLAGS_SIZE
+                    + FormatSpec.GROUP_ATTRIBUTE_MAX_ADDRESS_SIZE)
+                    * group.mBigrams.size();
+        }
+        return size;
+    }
+
+    /**
+     * Compute the maximum size of a node, assuming 3-byte addresses for everything, and caches
+     * it in the 'actualSize' member of the node.
+     *
+     * @param node the node to compute the maximum size of.
+     * @param options file format options.
+     */
+    private static void calculateNodeMaximumSize(final Node node, final FormatOptions options) {
+        int size = getGroupCountSize(node);
+        for (CharGroup g : node.mData) {
+            final int groupSize = getCharGroupMaximumSize(g, options);
+            g.mCachedSize = groupSize;
+            size += groupSize;
+        }
+        if (options.mSupportsDynamicUpdate) {
+            size += FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
+        }
+        node.mCachedSize = size;
+    }
+
+    /**
+     * Compute the size of the header (flag + [parent address] + characters size) of a CharGroup.
+     *
+     * @param group the group of which to compute the size of the header
+     * @param options file format options.
+     */
+    private static int getGroupHeaderSize(final CharGroup group, final FormatOptions options) {
+        if (BinaryDictIOUtils.supportsDynamicUpdate(options)) {
+            return FormatSpec.GROUP_FLAGS_SIZE + FormatSpec.PARENT_ADDRESS_SIZE
+                    + getGroupCharactersSize(group);
+        } else {
+            return FormatSpec.GROUP_FLAGS_SIZE + getGroupCharactersSize(group);
+        }
+    }
+
+    /**
+     * Compute the size, in bytes, that an address will occupy.
+     *
+     * This can be used either for children addresses (which are always positive) or for
+     * attribute, which may be positive or negative but
+     * store their sign bit separately.
+     *
+     * @param address the address
+     * @return the byte size.
+     */
+    static int getByteSize(final int address) {
+        assert(address <= FormatSpec.UINT24_MAX);
+        if (!BinaryDictIOUtils.hasChildrenAddress(address)) {
+            return 0;
+        } else if (Math.abs(address) <= FormatSpec.UINT8_MAX) {
+            return 1;
+        } else if (Math.abs(address) <= FormatSpec.UINT16_MAX) {
+            return 2;
+        } else {
+            return 3;
+        }
+    }
+
+    // End utility methods.
+
+    // This method is responsible for finding a nice ordering of the nodes that favors run-time
+    // cache performance and dictionary size.
+    /* package for tests */ static ArrayList<Node> flattenTree(final Node root) {
+        final int treeSize = FusionDictionary.countCharGroups(root);
+        MakedictLog.i("Counted nodes : " + treeSize);
+        final ArrayList<Node> flatTree = new ArrayList<Node>(treeSize);
+        return flattenTreeInner(flatTree, root);
+    }
+
+    private static ArrayList<Node> flattenTreeInner(final ArrayList<Node> list, final Node node) {
+        // Removing the node is necessary if the tails are merged, because we would then
+        // add the same node several times when we only want it once. A number of places in
+        // the code also depends on any node being only once in the list.
+        // Merging tails can only be done if there are no attributes. Searching for attributes
+        // in LatinIME code depends on a total breadth-first ordering, which merging tails
+        // breaks. If there are no attributes, it should be fine (and reduce the file size)
+        // to merge tails, and removing the node from the list would be necessary. However,
+        // we don't merge tails because breaking the breadth-first ordering would result in
+        // extreme overhead at bigram lookup time (it would make the search function O(n) instead
+        // of the current O(log(n)), where n=number of nodes in the dictionary which is pretty
+        // high).
+        // If no nodes are ever merged, we can't have the same node twice in the list, hence
+        // searching for duplicates in unnecessary. It is also very performance consuming,
+        // since `list' is an ArrayList so it's an O(n) operation that runs on all nodes, making
+        // this simple list.remove operation O(n*n) overall. On Android this overhead is very
+        // high.
+        // For future reference, the code to remove duplicate is a simple : list.remove(node);
+        list.add(node);
+        final ArrayList<CharGroup> branches = node.mData;
+        final int nodeSize = branches.size();
+        for (CharGroup group : branches) {
+            if (null != group.mChildren) flattenTreeInner(list, group.mChildren);
+        }
+        return list;
+    }
+
+    /**
+     * Get the offset from a position inside a current node to a target node, during update.
+     *
+     * If the current node is before the target node, the target node has not been updated yet,
+     * so we should return the offset from the old position of the current node to the old position
+     * of the target node. If on the other hand the target is before the current node, it already
+     * has been updated, so we should return the offset from the new position in the current node
+     * to the new position in the target node.
+     * @param currentNode the node containing the CharGroup where the offset will be written
+     * @param offsetFromStartOfCurrentNode the offset, in bytes, from the start of currentNode
+     * @param targetNode the target node to get the offset to
+     * @return the offset to the target node
+     */
+    private static int getOffsetToTargetNodeDuringUpdate(final Node currentNode,
+            final int offsetFromStartOfCurrentNode, final Node targetNode) {
+        final boolean isTargetBeforeCurrent = (targetNode.mCachedAddressBeforeUpdate
+                < currentNode.mCachedAddressBeforeUpdate);
+        if (isTargetBeforeCurrent) {
+            return targetNode.mCachedAddressAfterUpdate
+                    - (currentNode.mCachedAddressAfterUpdate + offsetFromStartOfCurrentNode);
+        } else {
+            return targetNode.mCachedAddressBeforeUpdate
+                    - (currentNode.mCachedAddressBeforeUpdate + offsetFromStartOfCurrentNode);
+        }
+    }
+
+    /**
+     * Get the offset from a position inside a current node to a target CharGroup, during update.
+     * @param currentNode the node containing the CharGroup where the offset will be written
+     * @param offsetFromStartOfCurrentNode the offset, in bytes, from the start of currentNode
+     * @param targetCharGroup the target CharGroup to get the offset to
+     * @return the offset to the target CharGroup
+     */
+    // TODO: is there any way to factorize this method with the one above?
+    private static int getOffsetToTargetCharGroupDuringUpdate(final Node currentNode,
+            final int offsetFromStartOfCurrentNode, final CharGroup targetCharGroup) {
+        final int oldOffsetBasePoint = currentNode.mCachedAddressBeforeUpdate
+                + offsetFromStartOfCurrentNode;
+        final boolean isTargetBeforeCurrent = (targetCharGroup.mCachedAddressBeforeUpdate
+                < oldOffsetBasePoint);
+        // If the target is before the current node, then its address has already been updated.
+        // We can use the AfterUpdate member, and compare it to our own member after update.
+        // Otherwise, the AfterUpdate member is not updated yet, so we need to use the BeforeUpdate
+        // member, and of course we have to compare this to our own address before update.
+        if (isTargetBeforeCurrent) {
+            final int newOffsetBasePoint = currentNode.mCachedAddressAfterUpdate
+                    + offsetFromStartOfCurrentNode;
+            return targetCharGroup.mCachedAddressAfterUpdate - newOffsetBasePoint;
+        } else {
+            return targetCharGroup.mCachedAddressBeforeUpdate - oldOffsetBasePoint;
+        }
+    }
+
+    /**
+     * Computes the actual node size, based on the cached addresses of the children nodes.
+     *
+     * Each node stores its tentative address. During dictionary address computing, these
+     * are not final, but they can be used to compute the node size (the node size depends
+     * on the address of the children because the number of bytes necessary to store an
+     * address depends on its numeric value. The return value indicates whether the node
+     * contents (as in, any of the addresses stored in the cache fields) have changed with
+     * respect to their previous value.
+     *
+     * @param node the node to compute the size of.
+     * @param dict the dictionary in which the word/attributes are to be found.
+     * @param formatOptions file format options.
+     * @return false if none of the cached addresses inside the node changed, true otherwise.
+     */
+    private static boolean computeActualNodeSize(final Node node, final FusionDictionary dict,
+            final FormatOptions formatOptions) {
+        boolean changed = false;
+        int size = getGroupCountSize(node);
+        for (CharGroup group : node.mData) {
+            group.mCachedAddressAfterUpdate = node.mCachedAddressAfterUpdate + size;
+            if (group.mCachedAddressAfterUpdate != group.mCachedAddressBeforeUpdate) {
+                changed = true;
+            }
+            int groupSize = getGroupHeaderSize(group, formatOptions);
+            if (group.isTerminal()) groupSize += FormatSpec.GROUP_FREQUENCY_SIZE;
+            if (null == group.mChildren && formatOptions.mSupportsDynamicUpdate) {
+                groupSize += FormatSpec.SIGNED_CHILDREN_ADDRESS_SIZE;
+            } else if (null != group.mChildren) {
+                if (formatOptions.mSupportsDynamicUpdate) {
+                    groupSize += FormatSpec.SIGNED_CHILDREN_ADDRESS_SIZE;
+                } else {
+                    groupSize += getByteSize(getOffsetToTargetNodeDuringUpdate(node,
+                            groupSize + size, group.mChildren));
+                }
+            }
+            groupSize += getShortcutListSize(group.mShortcutTargets);
+            if (null != group.mBigrams) {
+                for (WeightedString bigram : group.mBigrams) {
+                    final int offset = getOffsetToTargetCharGroupDuringUpdate(node,
+                            groupSize + size + FormatSpec.GROUP_FLAGS_SIZE,
+                            FusionDictionary.findWordInTree(dict.mRoot, bigram.mWord));
+                    groupSize += getByteSize(offset) + FormatSpec.GROUP_FLAGS_SIZE;
+                }
+            }
+            group.mCachedSize = groupSize;
+            size += groupSize;
+        }
+        if (formatOptions.mSupportsDynamicUpdate) {
+            size += FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
+        }
+        if (node.mCachedSize != size) {
+            node.mCachedSize = size;
+            changed = true;
+        }
+        return changed;
+    }
+
+    /**
+     * Initializes the cached addresses of nodes from their size.
+     *
+     * @param flatNodes the array of nodes.
+     * @param formatOptions file format options.
+     * @return the byte size of the entire stack.
+     */
+    private static int initializeNodesCachedAddresses(final ArrayList<Node> flatNodes,
+            final FormatOptions formatOptions) {
+        int nodeOffset = 0;
+        for (final Node n : flatNodes) {
+            n.mCachedAddressBeforeUpdate = nodeOffset;
+            int groupCountSize = getGroupCountSize(n);
+            int groupOffset = 0;
+            for (final CharGroup g : n.mData) {
+                g.mCachedAddressBeforeUpdate = g.mCachedAddressAfterUpdate =
+                        groupCountSize + nodeOffset + groupOffset;
+                groupOffset += g.mCachedSize;
+            }
+            final int nodeSize = groupCountSize + groupOffset
+                    + (formatOptions.mSupportsDynamicUpdate
+                            ? FormatSpec.FORWARD_LINK_ADDRESS_SIZE : 0);
+            nodeOffset += n.mCachedSize;
+        }
+        return nodeOffset;
+    }
+
+    /**
+     * Updates the cached addresses of nodes after recomputing their new positions.
+     *
+     * @param flatNodes the array of nodes.
+     */
+    private static void updateNodeCachedAddresses(final ArrayList<Node> flatNodes) {
+        for (final Node n : flatNodes) {
+            n.mCachedAddressBeforeUpdate = n.mCachedAddressAfterUpdate;
+            for (final CharGroup g : n.mData) {
+                g.mCachedAddressBeforeUpdate = g.mCachedAddressAfterUpdate;
+            }
+        }
+    }
+
+    /**
+     * Compute the cached parent addresses after all has been updated.
+     *
+     * The parent addresses are used by some binary formats at write-to-disk time. Not all formats
+     * need them. In particular, version 2 does not need them, and version 3 does.
+     *
+     * @param flatNodes the flat array of nodes to fill in
+     */
+    private static void computeParentAddresses(final ArrayList<Node> flatNodes) {
+        for (final Node node : flatNodes) {
+            for (final CharGroup group : node.mData) {
+                if (null != group.mChildren) {
+                    // Assign my address to children's parent address
+                    // Here BeforeUpdate and AfterUpdate addresses have the same value, so it
+                    // does not matter which we use.
+                    group.mChildren.mCachedParentAddress = group.mCachedAddressAfterUpdate
+                            - group.mChildren.mCachedAddressAfterUpdate;
+                }
+            }
+        }
+    }
+
+    /**
+     * Compute the addresses and sizes of an ordered node array.
+     *
+     * This method takes a node array and will update its cached address and size values
+     * so that they can be written into a file. It determines the smallest size each of the
+     * nodes can be given the addresses of its children and attributes, and store that into
+     * each node.
+     * The order of the node is given by the order of the array. This method makes no effort
+     * to find a good order; it only mechanically computes the size this order results in.
+     *
+     * @param dict the dictionary
+     * @param flatNodes the ordered array of nodes
+     * @param formatOptions file format options.
+     * @return the same array it was passed. The nodes have been updated for address and size.
+     */
+    private static ArrayList<Node> computeAddresses(final FusionDictionary dict,
+            final ArrayList<Node> flatNodes, final FormatOptions formatOptions) {
+        // First get the worst possible sizes and offsets
+        for (final Node n : flatNodes) calculateNodeMaximumSize(n, formatOptions);
+        final int offset = initializeNodesCachedAddresses(flatNodes, formatOptions);
+
+        MakedictLog.i("Compressing the array addresses. Original size : " + offset);
+        MakedictLog.i("(Recursively seen size : " + offset + ")");
+
+        int passes = 0;
+        boolean changesDone = false;
+        do {
+            changesDone = false;
+            int nodeStartOffset = 0;
+            for (final Node n : flatNodes) {
+                n.mCachedAddressAfterUpdate = nodeStartOffset;
+                final int oldNodeSize = n.mCachedSize;
+                final boolean changed = computeActualNodeSize(n, dict, formatOptions);
+                final int newNodeSize = n.mCachedSize;
+                if (oldNodeSize < newNodeSize) throw new RuntimeException("Increased size ?!");
+                nodeStartOffset += newNodeSize;
+                changesDone |= changed;
+            }
+            updateNodeCachedAddresses(flatNodes);
+            ++passes;
+            if (passes > MAX_PASSES) throw new RuntimeException("Too many passes - probably a bug");
+        } while (changesDone);
+
+        if (formatOptions.mSupportsDynamicUpdate) {
+            computeParentAddresses(flatNodes);
+        }
+        final Node lastNode = flatNodes.get(flatNodes.size() - 1);
+        MakedictLog.i("Compression complete in " + passes + " passes.");
+        MakedictLog.i("After address compression : "
+                + (lastNode.mCachedAddressAfterUpdate + lastNode.mCachedSize));
+
+        return flatNodes;
+    }
+
+    /**
+     * Sanity-checking method.
+     *
+     * This method checks an array of node for juxtaposition, that is, it will do
+     * nothing if each node's cached address is actually the previous node's address
+     * plus the previous node's size.
+     * If this is not the case, it will throw an exception.
+     *
+     * @param array the array node to check
+     */
+    private static void checkFlatNodeArray(final ArrayList<Node> array) {
+        int offset = 0;
+        int index = 0;
+        for (final Node n : array) {
+            // BeforeUpdate and AfterUpdate addresses are the same here, so it does not matter
+            // which we use.
+            if (n.mCachedAddressAfterUpdate != offset) {
+                throw new RuntimeException("Wrong address for node " + index
+                        + " : expected " + offset + ", got " + n.mCachedAddressAfterUpdate);
+            }
+            ++index;
+            offset += n.mCachedSize;
+        }
+    }
+
+    /**
+     * Helper method to write a variable-size address to a file.
+     *
+     * @param buffer the buffer to write to.
+     * @param index the index in the buffer to write the address to.
+     * @param address the address to write.
+     * @return the size in bytes the address actually took.
+     */
+    private static int writeVariableAddress(final byte[] buffer, int index, final int address) {
+        switch (getByteSize(address)) {
+        case 1:
+            buffer[index++] = (byte)address;
+            return 1;
+        case 2:
+            buffer[index++] = (byte)(0xFF & (address >> 8));
+            buffer[index++] = (byte)(0xFF & address);
+            return 2;
+        case 3:
+            buffer[index++] = (byte)(0xFF & (address >> 16));
+            buffer[index++] = (byte)(0xFF & (address >> 8));
+            buffer[index++] = (byte)(0xFF & address);
+            return 3;
+        case 0:
+            return 0;
+        default:
+            throw new RuntimeException("Address " + address + " has a strange size");
+        }
+    }
+
+    /**
+     * Helper method to write a variable-size signed address to a file.
+     *
+     * @param buffer the buffer to write to.
+     * @param index the index in the buffer to write the address to.
+     * @param address the address to write.
+     * @return the size in bytes the address actually took.
+     */
+    private static int writeVariableSignedAddress(final byte[] buffer, int index,
+            final int address) {
+        if (!BinaryDictIOUtils.hasChildrenAddress(address)) {
+            buffer[index] = buffer[index + 1] = buffer[index + 2] = 0;
+        } else {
+            final int absAddress = Math.abs(address);
+            buffer[index++] =
+                    (byte)((address < 0 ? FormatSpec.MSB8 : 0) | (0xFF & (absAddress >> 16)));
+            buffer[index++] = (byte)(0xFF & (absAddress >> 8));
+            buffer[index++] = (byte)(0xFF & absAddress);
+        }
+        return 3;
+    }
+
+    /**
+     * Makes the flag value for a char group.
+     *
+     * @param hasMultipleChars whether the group has multiple chars.
+     * @param isTerminal whether the group is terminal.
+     * @param childrenAddressSize the size of a children address.
+     * @param hasShortcuts whether the group has shortcuts.
+     * @param hasBigrams whether the group has bigrams.
+     * @param isNotAWord whether the group is not a word.
+     * @param isBlackListEntry whether the group is a blacklist entry.
+     * @param formatOptions file format options.
+     * @return the flags
+     */
+    static int makeCharGroupFlags(final boolean hasMultipleChars, final boolean isTerminal,
+            final int childrenAddressSize, final boolean hasShortcuts, final boolean hasBigrams,
+            final boolean isNotAWord, final boolean isBlackListEntry,
+            final FormatOptions formatOptions) {
+        byte flags = 0;
+        if (hasMultipleChars) flags |= FormatSpec.FLAG_HAS_MULTIPLE_CHARS;
+        if (isTerminal) flags |= FormatSpec.FLAG_IS_TERMINAL;
+        if (formatOptions.mSupportsDynamicUpdate) {
+            flags |= FormatSpec.FLAG_IS_NOT_MOVED;
+        } else if (true) {
+            switch (childrenAddressSize) {
+                case 1:
+                    flags |= FormatSpec.FLAG_GROUP_ADDRESS_TYPE_ONEBYTE;
+                    break;
+                case 2:
+                    flags |= FormatSpec.FLAG_GROUP_ADDRESS_TYPE_TWOBYTES;
+                    break;
+                case 3:
+                    flags |= FormatSpec.FLAG_GROUP_ADDRESS_TYPE_THREEBYTES;
+                    break;
+                case 0:
+                    flags |= FormatSpec.FLAG_GROUP_ADDRESS_TYPE_NOADDRESS;
+                    break;
+                default:
+                    throw new RuntimeException("Node with a strange address");
+            }
+        }
+        if (hasShortcuts) flags |= FormatSpec.FLAG_HAS_SHORTCUT_TARGETS;
+        if (hasBigrams) flags |= FormatSpec.FLAG_HAS_BIGRAMS;
+        if (isNotAWord) flags |= FormatSpec.FLAG_IS_NOT_A_WORD;
+        if (isBlackListEntry) flags |= FormatSpec.FLAG_IS_BLACKLISTED;
+        return flags;
+    }
+
+    private static byte makeCharGroupFlags(final CharGroup group, final int groupAddress,
+            final int childrenOffset, final FormatOptions formatOptions) {
+        return (byte) makeCharGroupFlags(group.mChars.length > 1, group.mFrequency >= 0,
+                getByteSize(childrenOffset), group.mShortcutTargets != null, group.mBigrams != null,
+                group.mIsNotAWord, group.mIsBlacklistEntry, formatOptions);
+    }
+
+    /**
+     * Makes the flag value for a bigram.
+     *
+     * @param more whether there are more bigrams after this one.
+     * @param offset the offset of the bigram.
+     * @param bigramFrequency the frequency of the bigram, 0..255.
+     * @param unigramFrequency the unigram frequency of the same word, 0..255.
+     * @param word the second bigram, for debugging purposes
+     * @return the flags
+     */
+    private static final int makeBigramFlags(final boolean more, final int offset,
+            int bigramFrequency, final int unigramFrequency, final String word) {
+        int bigramFlags = (more ? FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT : 0)
+                + (offset < 0 ? FormatSpec.FLAG_ATTRIBUTE_OFFSET_NEGATIVE : 0);
+        switch (getByteSize(offset)) {
+        case 1:
+            bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE;
+            break;
+        case 2:
+            bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES;
+            break;
+        case 3:
+            bigramFlags |= FormatSpec.FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES;
+            break;
+        default:
+            throw new RuntimeException("Strange offset size");
+        }
+        if (unigramFrequency > bigramFrequency) {
+            MakedictLog.e("Unigram freq is superior to bigram freq for \"" + word
+                    + "\". Bigram freq is " + bigramFrequency + ", unigram freq for "
+                    + word + " is " + unigramFrequency);
+            bigramFrequency = unigramFrequency;
+        }
+        // We compute the difference between 255 (which means probability = 1) and the
+        // unigram score. We split this into a number of discrete steps.
+        // Now, the steps are numbered 0~15; 0 represents an increase of 1 step while 15
+        // represents an increase of 16 steps: a value of 15 will be interpreted as the median
+        // value of the 16th step. In all justice, if the bigram frequency is low enough to be
+        // rounded below the first step (which means it is less than half a step higher than the
+        // unigram frequency) then the unigram frequency itself is the best approximation of the
+        // bigram freq that we could possibly supply, hence we should *not* include this bigram
+        // in the file at all.
+        // until this is done, we'll write 0 and slightly overestimate this case.
+        // In other words, 0 means "between 0.5 step and 1.5 step", 1 means "between 1.5 step
+        // and 2.5 steps", and 15 means "between 15.5 steps and 16.5 steps". So we want to
+        // divide our range [unigramFreq..MAX_TERMINAL_FREQUENCY] in 16.5 steps to get the
+        // step size. Then we compute the start of the first step (the one where value 0 starts)
+        // by adding half-a-step to the unigramFrequency. From there, we compute the integer
+        // number of steps to the bigramFrequency. One last thing: we want our steps to include
+        // their lower bound and exclude their higher bound so we need to have the first step
+        // start at exactly 1 unit higher than floor(unigramFreq + half a step).
+        // Note : to reconstruct the score, the dictionary reader will need to divide
+        // MAX_TERMINAL_FREQUENCY - unigramFreq by 16.5 likewise to get the value of the step,
+        // and add (discretizedFrequency + 0.5 + 0.5) times this value to get the best
+        // approximation. (0.5 to get the first step start, and 0.5 to get the middle of the
+        // step pointed by the discretized frequency.
+        final float stepSize =
+                (FormatSpec.MAX_TERMINAL_FREQUENCY - unigramFrequency)
+                / (1.5f + FormatSpec.MAX_BIGRAM_FREQUENCY);
+        final float firstStepStart = 1 + unigramFrequency + (stepSize / 2.0f);
+        final int discretizedFrequency = (int)((bigramFrequency - firstStepStart) / stepSize);
+        // If the bigram freq is less than half-a-step higher than the unigram freq, we get -1
+        // here. The best approximation would be the unigram freq itself, so we should not
+        // include this bigram in the dictionary. For now, register as 0, and live with the
+        // small over-estimation that we get in this case. TODO: actually remove this bigram
+        // if discretizedFrequency < 0.
+        final int finalBigramFrequency = discretizedFrequency > 0 ? discretizedFrequency : 0;
+        bigramFlags += finalBigramFrequency & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY;
+        return bigramFlags;
+    }
+
+    /**
+     * Makes the 2-byte value for options flags.
+     */
+    private static final int makeOptionsValue(final FusionDictionary dictionary,
+            final FormatOptions formatOptions) {
+        final DictionaryOptions options = dictionary.mOptions;
+        final boolean hasBigrams = dictionary.hasBigrams();
+        return (options.mFrenchLigatureProcessing ? FormatSpec.FRENCH_LIGATURE_PROCESSING_FLAG : 0)
+                + (options.mGermanUmlautProcessing ? FormatSpec.GERMAN_UMLAUT_PROCESSING_FLAG : 0)
+                + (hasBigrams ? FormatSpec.CONTAINS_BIGRAMS_FLAG : 0)
+                + (formatOptions.mSupportsDynamicUpdate ? FormatSpec.SUPPORTS_DYNAMIC_UPDATE : 0);
+    }
+
+    /**
+     * Makes the flag value for a shortcut.
+     *
+     * @param more whether there are more attributes after this one.
+     * @param frequency the frequency of the attribute, 0..15
+     * @return the flags
+     */
+    static final int makeShortcutFlags(final boolean more, final int frequency) {
+        return (more ? FormatSpec.FLAG_ATTRIBUTE_HAS_NEXT : 0)
+                + (frequency & FormatSpec.FLAG_ATTRIBUTE_FREQUENCY);
+    }
+
+    private static final int writeParentAddress(final byte[] buffer, final int index,
+            final int address, final FormatOptions formatOptions) {
+        if (BinaryDictIOUtils.supportsDynamicUpdate(formatOptions)) {
+            if (address == FormatSpec.NO_PARENT_ADDRESS) {
+                buffer[index] = buffer[index + 1] = buffer[index + 2] = 0;
+            } else {
+                final int absAddress = Math.abs(address);
+                assert(absAddress <= FormatSpec.SINT24_MAX);
+                buffer[index] = (byte)((address < 0 ? FormatSpec.MSB8 : 0)
+                        | ((absAddress >> 16) & 0xFF));
+                buffer[index + 1] = (byte)((absAddress >> 8) & 0xFF);
+                buffer[index + 2] = (byte)(absAddress & 0xFF);
+            }
+            return index + 3;
+        } else {
+            return index;
+        }
+    }
+
+    /**
+     * Write a node to memory. The node is expected to have its final position cached.
+     *
+     * This can be an empty map, but the more is inside the faster the lookups will be. It can
+     * be carried on as long as nodes do not move.
+     *
+     * @param dict the dictionary the node is a part of (for relative offsets).
+     * @param buffer the memory buffer to write to.
+     * @param node the node to write.
+     * @param formatOptions file format options.
+     * @return the address of the END of the node.
+     */
+    @SuppressWarnings("unused")
+    private static int writePlacedNode(final FusionDictionary dict, byte[] buffer,
+            final Node node, final FormatOptions formatOptions) {
+        // TODO: Make the code in common with BinaryDictIOUtils#writeCharGroup
+        int index = node.mCachedAddressAfterUpdate;
+
+        final int groupCount = node.mData.size();
+        final int countSize = getGroupCountSize(node);
+        final int parentAddress = node.mCachedParentAddress;
+        if (1 == countSize) {
+            buffer[index++] = (byte)groupCount;
+        } else if (2 == countSize) {
+            // We need to signal 2-byte size by setting the top bit of the MSB to 1, so
+            // we | 0x80 to do this.
+            buffer[index++] = (byte)((groupCount >> 8) | 0x80);
+            buffer[index++] = (byte)(groupCount & 0xFF);
+        } else {
+            throw new RuntimeException("Strange size from getGroupCountSize : " + countSize);
+        }
+        int groupAddress = index;
+        for (int i = 0; i < groupCount; ++i) {
+            final CharGroup group = node.mData.get(i);
+            if (index != group.mCachedAddressAfterUpdate) {
+                throw new RuntimeException("Bug: write index is not the same as the cached address "
+                        + "of the group : " + index + " <> " + group.mCachedAddressAfterUpdate);
+            }
+            groupAddress += getGroupHeaderSize(group, formatOptions);
+            // Sanity checks.
+            if (DBG && group.mFrequency > FormatSpec.MAX_TERMINAL_FREQUENCY) {
+                throw new RuntimeException("A node has a frequency > "
+                        + FormatSpec.MAX_TERMINAL_FREQUENCY
+                        + " : " + group.mFrequency);
+            }
+            if (group.mFrequency >= 0) groupAddress += FormatSpec.GROUP_FREQUENCY_SIZE;
+            final int childrenOffset = null == group.mChildren
+                    ? FormatSpec.NO_CHILDREN_ADDRESS
+                            : group.mChildren.mCachedAddressAfterUpdate - groupAddress;
+            buffer[index++] =
+                    makeCharGroupFlags(group, groupAddress, childrenOffset, formatOptions);
+
+            if (parentAddress == FormatSpec.NO_PARENT_ADDRESS) {
+                index = writeParentAddress(buffer, index, parentAddress, formatOptions);
+            } else {
+                index = writeParentAddress(buffer, index, parentAddress
+                        + (node.mCachedAddressAfterUpdate - group.mCachedAddressAfterUpdate),
+                        formatOptions);
+            }
+
+            index = CharEncoding.writeCharArray(group.mChars, buffer, index);
+            if (group.hasSeveralChars()) {
+                buffer[index++] = FormatSpec.GROUP_CHARACTERS_TERMINATOR;
+            }
+            if (group.mFrequency >= 0) {
+                buffer[index++] = (byte) group.mFrequency;
+            }
+
+            final int shift;
+            if (formatOptions.mSupportsDynamicUpdate) {
+                shift = writeVariableSignedAddress(buffer, index, childrenOffset);
+            } else {
+                shift = writeVariableAddress(buffer, index, childrenOffset);
+            }
+            index += shift;
+            groupAddress += shift;
+
+            // Write shortcuts
+            if (null != group.mShortcutTargets) {
+                final int indexOfShortcutByteSize = index;
+                index += FormatSpec.GROUP_SHORTCUT_LIST_SIZE_SIZE;
+                groupAddress += FormatSpec.GROUP_SHORTCUT_LIST_SIZE_SIZE;
+                final Iterator<WeightedString> shortcutIterator = group.mShortcutTargets.iterator();
+                while (shortcutIterator.hasNext()) {
+                    final WeightedString target = shortcutIterator.next();
+                    ++groupAddress;
+                    int shortcutFlags = makeShortcutFlags(shortcutIterator.hasNext(),
+                            target.mFrequency);
+                    buffer[index++] = (byte)shortcutFlags;
+                    final int shortcutShift = CharEncoding.writeString(buffer, index, target.mWord);
+                    index += shortcutShift;
+                    groupAddress += shortcutShift;
+                }
+                final int shortcutByteSize = index - indexOfShortcutByteSize;
+                if (shortcutByteSize > 0xFFFF) {
+                    throw new RuntimeException("Shortcut list too large");
+                }
+                buffer[indexOfShortcutByteSize] = (byte)(shortcutByteSize >> 8);
+                buffer[indexOfShortcutByteSize + 1] = (byte)(shortcutByteSize & 0xFF);
+            }
+            // Write bigrams
+            if (null != group.mBigrams) {
+                final Iterator<WeightedString> bigramIterator = group.mBigrams.iterator();
+                while (bigramIterator.hasNext()) {
+                    final WeightedString bigram = bigramIterator.next();
+                    final CharGroup target =
+                            FusionDictionary.findWordInTree(dict.mRoot, bigram.mWord);
+                    final int addressOfBigram = target.mCachedAddressAfterUpdate;
+                    final int unigramFrequencyForThisWord = target.mFrequency;
+                    ++groupAddress;
+                    final int offset = addressOfBigram - groupAddress;
+                    int bigramFlags = makeBigramFlags(bigramIterator.hasNext(), offset,
+                            bigram.mFrequency, unigramFrequencyForThisWord, bigram.mWord);
+                    buffer[index++] = (byte)bigramFlags;
+                    final int bigramShift = writeVariableAddress(buffer, index, Math.abs(offset));
+                    index += bigramShift;
+                    groupAddress += bigramShift;
+                }
+            }
+
+        }
+        if (formatOptions.mSupportsDynamicUpdate) {
+            buffer[index] = buffer[index + 1] = buffer[index + 2]
+                    = FormatSpec.NO_FORWARD_LINK_ADDRESS;
+            index += FormatSpec.FORWARD_LINK_ADDRESS_SIZE;
+        }
+        if (index != node.mCachedAddressAfterUpdate + node.mCachedSize) throw new RuntimeException(
+                "Not the same size : written "
+                + (index - node.mCachedAddressAfterUpdate) + " bytes from a node that should have "
+                + node.mCachedSize + " bytes");
+        return index;
+    }
+
+    /**
+     * Dumps a collection of useful statistics about a node array.
+     *
+     * This prints purely informative stuff, like the total estimated file size, the
+     * number of nodes, of character groups, the repartition of each address size, etc
+     *
+     * @param nodes the node array.
+     */
+    private static void showStatistics(ArrayList<Node> nodes) {
+        int firstTerminalAddress = Integer.MAX_VALUE;
+        int lastTerminalAddress = Integer.MIN_VALUE;
+        int size = 0;
+        int charGroups = 0;
+        int maxGroups = 0;
+        int maxRuns = 0;
+        for (final Node n : nodes) {
+            if (maxGroups < n.mData.size()) maxGroups = n.mData.size();
+            for (final CharGroup cg : n.mData) {
+                ++charGroups;
+                if (cg.mChars.length > maxRuns) maxRuns = cg.mChars.length;
+                if (cg.mFrequency >= 0) {
+                    if (n.mCachedAddressAfterUpdate < firstTerminalAddress)
+                        firstTerminalAddress = n.mCachedAddressAfterUpdate;
+                    if (n.mCachedAddressAfterUpdate > lastTerminalAddress)
+                        lastTerminalAddress = n.mCachedAddressAfterUpdate;
+                }
+            }
+            if (n.mCachedAddressAfterUpdate + n.mCachedSize > size) {
+                size = n.mCachedAddressAfterUpdate + n.mCachedSize;
+            }
+        }
+        final int[] groupCounts = new int[maxGroups + 1];
+        final int[] runCounts = new int[maxRuns + 1];
+        for (final Node n : nodes) {
+            ++groupCounts[n.mData.size()];
+            for (final CharGroup cg : n.mData) {
+                ++runCounts[cg.mChars.length];
+            }
+        }
+
+        MakedictLog.i("Statistics:\n"
+                + "  total file size " + size + "\n"
+                + "  " + nodes.size() + " nodes\n"
+                + "  " + charGroups + " groups (" + ((float)charGroups / nodes.size())
+                        + " groups per node)\n"
+                + "  first terminal at " + firstTerminalAddress + "\n"
+                + "  last terminal at " + lastTerminalAddress + "\n"
+                + "  Group stats : max = " + maxGroups);
+        for (int i = 0; i < groupCounts.length; ++i) {
+            MakedictLog.i("    " + i + " : " + groupCounts[i]);
+        }
+        MakedictLog.i("  Character run stats : max = " + maxRuns);
+        for (int i = 0; i < runCounts.length; ++i) {
+            MakedictLog.i("    " + i + " : " + runCounts[i]);
+        }
+    }
+
+    /**
+     * Dumps a FusionDictionary to a file.
+     *
+     * This is the public entry point to write a dictionary to a file.
+     *
+     * @param destination the stream to write the binary data to.
+     * @param dict the dictionary to write.
+     * @param formatOptions file format options.
+     */
+    public static void writeDictionaryBinary(final OutputStream destination,
+            final FusionDictionary dict, final FormatOptions formatOptions)
+            throws IOException, UnsupportedFormatException {
+
+        // Addresses are limited to 3 bytes, but since addresses can be relative to each node, the
+        // structure itself is not limited to 16MB. However, if it is over 16MB deciding the order
+        // of the nodes becomes a quite complicated problem, because though the dictionary itself
+        // does not have a size limit, each node must still be within 16MB of all its children and
+        // parents. As long as this is ensured, the dictionary file may grow to any size.
+
+        final int version = formatOptions.mVersion;
+        if (version < FormatSpec.MINIMUM_SUPPORTED_VERSION
+                || version > FormatSpec.MAXIMUM_SUPPORTED_VERSION) {
+            throw new UnsupportedFormatException("Requested file format version " + version
+                    + ", but this implementation only supports versions "
+                    + FormatSpec.MINIMUM_SUPPORTED_VERSION + " through "
+                    + FormatSpec.MAXIMUM_SUPPORTED_VERSION);
+        }
+
+        ByteArrayOutputStream headerBuffer = new ByteArrayOutputStream(256);
+
+        // The magic number in big-endian order.
+        // Magic number for all versions.
+        headerBuffer.write((byte) (0xFF & (FormatSpec.MAGIC_NUMBER >> 24)));
+        headerBuffer.write((byte) (0xFF & (FormatSpec.MAGIC_NUMBER >> 16)));
+        headerBuffer.write((byte) (0xFF & (FormatSpec.MAGIC_NUMBER >> 8)));
+        headerBuffer.write((byte) (0xFF & FormatSpec.MAGIC_NUMBER));
+        // Dictionary version.
+        headerBuffer.write((byte) (0xFF & (version >> 8)));
+        headerBuffer.write((byte) (0xFF & version));
+
+        // Options flags
+        final int options = makeOptionsValue(dict, formatOptions);
+        headerBuffer.write((byte) (0xFF & (options >> 8)));
+        headerBuffer.write((byte) (0xFF & options));
+        final int headerSizeOffset = headerBuffer.size();
+        // Placeholder to be written later with header size.
+        for (int i = 0; i < 4; ++i) {
+            headerBuffer.write(0);
+        }
+        // Write out the options.
+        for (final String key : dict.mOptions.mAttributes.keySet()) {
+            final String value = dict.mOptions.mAttributes.get(key);
+            CharEncoding.writeString(headerBuffer, key);
+            CharEncoding.writeString(headerBuffer, value);
+        }
+        final int size = headerBuffer.size();
+        final byte[] bytes = headerBuffer.toByteArray();
+        // Write out the header size.
+        bytes[headerSizeOffset] = (byte) (0xFF & (size >> 24));
+        bytes[headerSizeOffset + 1] = (byte) (0xFF & (size >> 16));
+        bytes[headerSizeOffset + 2] = (byte) (0xFF & (size >> 8));
+        bytes[headerSizeOffset + 3] = (byte) (0xFF & (size >> 0));
+        destination.write(bytes);
+
+        headerBuffer.close();
+
+        // Leave the choice of the optimal node order to the flattenTree function.
+        MakedictLog.i("Flattening the tree...");
+        ArrayList<Node> flatNodes = flattenTree(dict.mRoot);
+
+        MakedictLog.i("Computing addresses...");
+        computeAddresses(dict, flatNodes, formatOptions);
+        MakedictLog.i("Checking array...");
+        if (DBG) checkFlatNodeArray(flatNodes);
+
+        // Create a buffer that matches the final dictionary size.
+        final Node lastNode = flatNodes.get(flatNodes.size() - 1);
+        final int bufferSize = lastNode.mCachedAddressAfterUpdate + lastNode.mCachedSize;
+        final byte[] buffer = new byte[bufferSize];
+        int index = 0;
+
+        MakedictLog.i("Writing file...");
+        int dataEndOffset = 0;
+        for (Node n : flatNodes) {
+            dataEndOffset = writePlacedNode(dict, buffer, n, formatOptions);
+        }
+
+        if (DBG) showStatistics(flatNodes);
+
+        destination.write(buffer, 0, dataEndOffset);
+
+        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;
+    }
+}