Move makedict to LatinIME android keyboard.

Bug: 6188977
Change-Id: I4d2ef504bb983abbda3cb52ee450cb46f58d95cf

1 files changed, 1208 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..42dd4df34
--- /dev/null
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictInputOutput.java
@@ -0,0 +1,1208 @@
+/*
+ * 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.latin.makedict.FusionDictionary.CharGroup;
+import com.android.inputmethod.latin.makedict.FusionDictionary.Node;
+import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.RandomAccessFile;
+import java.util.ArrayList;
+import java.util.Arrays;
+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 class BinaryDictInputOutput {
+
+    /* Node layout is as follows:
+     *   | addressType                         xx     : mask with MASK_GROUP_ADDRESS_TYPE
+     *                                 2 bits, 00 = no children : FLAG_GROUP_ADDRESS_TYPE_NOADDRESS
+     * f |                                     01 = 1 byte      : FLAG_GROUP_ADDRESS_TYPE_ONEBYTE
+     * l |                                     10 = 2 bytes     : FLAG_GROUP_ADDRESS_TYPE_TWOBYTES
+     * a |                                     11 = 3 bytes     : FLAG_GROUP_ADDRESS_TYPE_THREEBYTES
+     * g | has several chars ?         1 bit, 1 = yes, 0 = no   : FLAG_HAS_MULTIPLE_CHARS
+     * s | has a terminal ?            1 bit, 1 = yes, 0 = no   : FLAG_IS_TERMINAL
+     *   | has shortcut targets ?      1 bit, 1 = yes, 0 = no   : FLAG_HAS_SHORTCUT_TARGETS
+     *   | has bigrams ?               1 bit, 1 = yes, 0 = no   : FLAG_HAS_BIGRAMS
+     *   | is shortcut only ?          1 bit, 1 = yes, 0 = no   : FLAG_IS_SHORTCUT_ONLY
+     *
+     * c | IF FLAG_HAS_MULTIPLE_CHARS
+     * h |   char, char, char, char    n * (1 or 3 bytes) : use CharGroupInfo for i/o helpers
+     * a |   end                       1 byte, = 0
+     * r | ELSE
+     * s |   char                      1 or 3 bytes
+     *   | END
+     *
+     * f |
+     * r | IF FLAG_IS_TERMINAL
+     * e |   frequency                 1 byte
+     * q |
+     *
+     * c | IF 00 = FLAG_GROUP_ADDRESS_TYPE_NOADDRESS = addressType
+     * h |   // nothing
+     * i | ELSIF 01 = FLAG_GROUP_ADDRESS_TYPE_ONEBYTE == addressType
+     * l |   children address, 1 byte
+     * d | ELSIF 10 = FLAG_GROUP_ADDRESS_TYPE_TWOBYTES == addressType
+     * r |   children address, 2 bytes
+     * e | ELSE // 11 = FLAG_GROUP_ADDRESS_TYPE_THREEBYTES = addressType
+     * n |   children address, 3 bytes
+     * A | END
+     * d
+     * dress
+     *
+     *   | IF FLAG_IS_TERMINAL && FLAG_HAS_SHORTCUT_TARGETS
+     *   | shortcut targets address list
+     *   | IF FLAG_IS_TERMINAL && FLAG_HAS_BIGRAMS
+     *   | bigrams address list
+     *
+     * 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).
+     *
+     * bigram and shortcut address list is:
+     * <flags> = | hasNext = 1 bit, 1 = yes, 0 = no     : FLAG_ATTRIBUTE_HAS_NEXT
+     *           | addressSign = 1 bit,                 : FLAG_ATTRIBUTE_OFFSET_NEGATIVE
+     *           |                      1 = must take -address, 0 = must take +address
+     *           |                         xx : mask with MASK_ATTRIBUTE_ADDRESS_TYPE
+     *           | addressFormat = 2 bits, 00 = unused  : FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE
+     *           |                         01 = 1 byte  : FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE
+     *           |                         10 = 2 bytes : FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES
+     *           |                         11 = 3 bytes : FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES
+     *           | 4 bits : frequency         : mask with FLAG_ATTRIBUTE_FREQUENCY
+     * <address> | IF (01 == FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE == addressFormat)
+     *           |   read 1 byte, add top 4 bits
+     *           | ELSIF (10 == FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES == addressFormat)
+     *           |   read 2 bytes, add top 4 bits
+     *           | ELSE // 11 == FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES == addressFormat
+     *           |   read 3 bytes, add top 4 bits
+     *           | END
+     *           | if (FLAG_ATTRIBUTE_OFFSET_NEGATIVE) then address = -address
+     * if (FLAG_ATTRIBUTE_HAS_NET) goto bigram_and_shortcut_address_list_is
+     *
+     */
+
+    private static final int VERSION_1_MAGIC_NUMBER = 0x78B1;
+    private static final int VERSION_2_MAGIC_NUMBER = 0x9BC13AFE;
+    private static final int MINIMUM_SUPPORTED_VERSION = 1;
+    private static final int MAXIMUM_SUPPORTED_VERSION = 2;
+    private static final int NOT_A_VERSION_NUMBER = -1;
+    private static final int FIRST_VERSION_WITH_HEADER_SIZE = 2;
+
+    // No options yet, reserved for future use.
+    private static final int OPTIONS = 0;
+
+    // TODO: Make this value adaptative to content data, store it in the header, and
+    // use it in the reading code.
+    private static final int MAX_WORD_LENGTH = 48;
+
+    private static final int MASK_GROUP_ADDRESS_TYPE = 0xC0;
+    private static final int FLAG_GROUP_ADDRESS_TYPE_NOADDRESS = 0x00;
+    private static final int FLAG_GROUP_ADDRESS_TYPE_ONEBYTE = 0x40;
+    private static final int FLAG_GROUP_ADDRESS_TYPE_TWOBYTES = 0x80;
+    private static final int FLAG_GROUP_ADDRESS_TYPE_THREEBYTES = 0xC0;
+
+    private static final int FLAG_HAS_MULTIPLE_CHARS = 0x20;
+
+    private static final int FLAG_IS_TERMINAL = 0x10;
+    private static final int FLAG_HAS_SHORTCUT_TARGETS = 0x08;
+    private static final int FLAG_HAS_BIGRAMS = 0x04;
+    private static final int FLAG_IS_SHORTCUT_ONLY = 0x02;
+
+    private static final int FLAG_ATTRIBUTE_HAS_NEXT = 0x80;
+    private static final int FLAG_ATTRIBUTE_OFFSET_NEGATIVE = 0x40;
+    private static final int MASK_ATTRIBUTE_ADDRESS_TYPE = 0x30;
+    private static final int FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE = 0x10;
+    private static final int FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES = 0x20;
+    private static final int FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES = 0x30;
+    private static final int FLAG_ATTRIBUTE_FREQUENCY = 0x0F;
+
+    private static final int GROUP_CHARACTERS_TERMINATOR = 0x1F;
+
+    private static final int GROUP_TERMINATOR_SIZE = 1;
+    private static final int GROUP_FLAGS_SIZE = 1;
+    private static final int GROUP_FREQUENCY_SIZE = 1;
+    private static final int GROUP_MAX_ADDRESS_SIZE = 3;
+    private static final int GROUP_ATTRIBUTE_FLAGS_SIZE = 1;
+    private static final int GROUP_ATTRIBUTE_MAX_ADDRESS_SIZE = 3;
+
+    private static final int NO_CHILDREN_ADDRESS = Integer.MIN_VALUE;
+    private static final int INVALID_CHARACTER = -1;
+
+    private static final int MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT = 0x7F; // 127
+    private static final int MAX_CHARGROUPS_IN_A_NODE = 0x7FFF; // 32767
+
+    private static final int MAX_TERMINAL_FREQUENCY = 255;
+
+    /**
+     * A class grouping utility function for our specific character encoding.
+     */
+    private static 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(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.
+         */
+        private static int getCharSize(int character) {
+            // See char encoding in FusionDictionary.java
+            if (fitsOnOneByte(character)) return 1;
+            if (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 characters the character 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(int[] characters, byte[] buffer, int index) {
+            for (int character : characters) {
+                if (1 == getCharSize(character)) {
+                    buffer[index++] = (byte)character;
+                } else {
+                    buffer[index++] = (byte)(0xFF & (character >> 16));
+                    buffer[index++] = (byte)(0xFF & (character >> 8));
+                    buffer[index++] = (byte)(0xFF & character);
+                }
+            }
+            return index;
+        }
+
+        /**
+         * Reads a character from the file.
+         *
+         * This follows the character format documented earlier in this source file.
+         *
+         * @param source the file, positioned over an encoded character.
+         * @return the character code.
+         */
+        private static int readChar(RandomAccessFile source) throws IOException {
+            int character = source.readUnsignedByte();
+            if (!fitsOnOneByte(character)) {
+                if (GROUP_CHARACTERS_TERMINATOR == character)
+                    return INVALID_CHARACTER;
+                character <<= 16;
+                character += source.readUnsignedShort();
+            }
+            return character;
+        }
+    }
+
+    /**
+     * 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(CharGroup group) {
+        int size = CharEncoding.getCharArraySize(group.mChars);
+        if (group.hasSeveralChars()) size += GROUP_TERMINATOR_SIZE;
+        return size;
+    }
+
+    /**
+     * Compute the binary size of the group count
+     * @param count the group count
+     * @return the size of the group count, either 1 or 2 bytes.
+     */
+    private static int getGroupCountSize(final int count) {
+        if (MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT >= count) {
+            return 1;
+        } else if (MAX_CHARGROUPS_IN_A_NODE >= count) {
+            return 2;
+        } else {
+            throw new RuntimeException("Can't have more than " + MAX_CHARGROUPS_IN_A_NODE
+                    + " groups in a node (found " + count +")");
+        }
+    }
+
+    /**
+     * 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 getGroupCountSize(node.mData.size());
+    }
+
+    /**
+     * Compute the maximum size of a CharGroup, assuming 3-byte addresses for everything.
+     *
+     * @param group the CharGroup to compute the size of.
+     * @return the maximum size of the group.
+     */
+    private static int getCharGroupMaximumSize(CharGroup group) {
+        int size = getGroupCharactersSize(group) + GROUP_FLAGS_SIZE;
+        // If terminal, one byte for the frequency
+        if (group.isTerminal()) size += GROUP_FREQUENCY_SIZE;
+        size += GROUP_MAX_ADDRESS_SIZE; // For children address
+        if (null != group.mShortcutTargets) {
+            size += (GROUP_ATTRIBUTE_FLAGS_SIZE + GROUP_ATTRIBUTE_MAX_ADDRESS_SIZE)
+                    * group.mShortcutTargets.size();
+        }
+        if (null != group.mBigrams) {
+            size += (GROUP_ATTRIBUTE_FLAGS_SIZE + 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.
+     */
+    private static void setNodeMaximumSize(Node node) {
+        int size = getGroupCountSize(node);
+        for (CharGroup g : node.mData) {
+            final int groupSize = getCharGroupMaximumSize(g);
+            g.mCachedSize = groupSize;
+            size += groupSize;
+        }
+        node.mCachedSize = size;
+    }
+
+    /**
+     * Helper method to hide the actual value of the no children address.
+     */
+    private static boolean hasChildrenAddress(int address) {
+        return NO_CHILDREN_ADDRESS != address;
+    }
+
+    /**
+     * Helper method to find out if a character info is a shortcut only.
+     */
+    private static boolean isShortcutOnly(final CharGroupInfo info) {
+        return 0 != (info.mFlags & FLAG_IS_SHORTCUT_ONLY);
+    }
+
+    /**
+     * 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.
+     */
+    private static int getByteSize(int address) {
+        assert(address < 0x1000000);
+        if (!hasChildrenAddress(address)) {
+            return 0;
+        } else if (Math.abs(address) < 0x100) {
+            return 1;
+        } else if (Math.abs(address) < 0x10000) {
+            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(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(ArrayList<Node> list, 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 the following step would be necessary.
+        // If eventually the code runs on Android, searching through the whole array each time
+        // may be a performance concern.
+        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;
+    }
+
+    /**
+     * Finds the absolute address of a word in the dictionary.
+     *
+     * @param dict the dictionary in which to search.
+     * @param word the word we are searching for.
+     * @return the word address. If it is not found, an exception is thrown.
+     */
+    private static int findAddressOfWord(final FusionDictionary dict, final String word) {
+        return FusionDictionary.findWordInTree(dict.mRoot, word).mCachedAddress;
+    }
+
+    /**
+     * 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.
+     *
+     * @param node the node to compute the size of.
+     * @param dict the dictionary in which the word/attributes are to be found.
+     */
+    private static void computeActualNodeSize(Node node, FusionDictionary dict) {
+        int size = getGroupCountSize(node);
+        for (CharGroup group : node.mData) {
+            int groupSize = GROUP_FLAGS_SIZE + getGroupCharactersSize(group);
+            if (group.isTerminal()) groupSize += GROUP_FREQUENCY_SIZE;
+            if (null != group.mChildren) {
+                final int offsetBasePoint= groupSize + node.mCachedAddress + size;
+                final int offset = group.mChildren.mCachedAddress - offsetBasePoint;
+                groupSize += getByteSize(offset);
+            }
+            if (null != group.mShortcutTargets) {
+                for (WeightedString target : group.mShortcutTargets) {
+                    final int offsetBasePoint = groupSize + node.mCachedAddress + size
+                            + GROUP_FLAGS_SIZE;
+                    final int addressOfTarget = findAddressOfWord(dict, target.mWord);
+                    final int offset = addressOfTarget - offsetBasePoint;
+                    groupSize += getByteSize(offset) + GROUP_FLAGS_SIZE;
+                }
+            }
+            if (null != group.mBigrams) {
+                for (WeightedString bigram : group.mBigrams) {
+                    final int offsetBasePoint = groupSize + node.mCachedAddress + size
+                            + GROUP_FLAGS_SIZE;
+                    final int addressOfBigram = findAddressOfWord(dict, bigram.mWord);
+                    final int offset = addressOfBigram - offsetBasePoint;
+                    groupSize += getByteSize(offset) + GROUP_FLAGS_SIZE;
+                }
+            }
+            group.mCachedSize = groupSize;
+            size += groupSize;
+        }
+        node.mCachedSize = size;
+    }
+
+    /**
+     * Computes the byte size of a list of nodes and updates each node cached position.
+     *
+     * @param flatNodes the array of nodes.
+     * @return the byte size of the entire stack.
+     */
+    private static int stackNodes(ArrayList<Node> flatNodes) {
+        int nodeOffset = 0;
+        for (Node n : flatNodes) {
+            n.mCachedAddress = nodeOffset;
+            int groupCountSize = getGroupCountSize(n);
+            int groupOffset = 0;
+            for (CharGroup g : n.mData) {
+                g.mCachedAddress = groupCountSize + nodeOffset + groupOffset;
+                groupOffset += g.mCachedSize;
+            }
+            if (groupOffset + groupCountSize != n.mCachedSize) {
+                throw new RuntimeException("Bug : Stored and computed node size differ");
+            }
+            nodeOffset += n.mCachedSize;
+        }
+        return nodeOffset;
+    }
+
+    /**
+     * 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
+     * @return the same array it was passed. The nodes have been updated for address and size.
+     */
+    private static ArrayList<Node> computeAddresses(FusionDictionary dict,
+            ArrayList<Node> flatNodes) {
+        // First get the worst sizes and offsets
+        for (Node n : flatNodes) setNodeMaximumSize(n);
+        final int offset = stackNodes(flatNodes);
+
+        MakedictLog.i("Compressing the array addresses. Original size : " + offset);
+        MakedictLog.i("(Recursively seen size : " + offset + ")");
+
+        int passes = 0;
+        boolean changesDone = false;
+        do {
+            changesDone = false;
+            for (Node n : flatNodes) {
+                final int oldNodeSize = n.mCachedSize;
+                computeActualNodeSize(n, dict);
+                final int newNodeSize = n.mCachedSize;
+                if (oldNodeSize < newNodeSize) throw new RuntimeException("Increased size ?!");
+                if (oldNodeSize != newNodeSize) changesDone = true;
+            }
+            stackNodes(flatNodes);
+            ++passes;
+        } while (changesDone);
+
+        final Node lastNode = flatNodes.get(flatNodes.size() - 1);
+        MakedictLog.i("Compression complete in " + passes + " passes.");
+        MakedictLog.i("After address compression : "
+                + (lastNode.mCachedAddress + 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(ArrayList<Node> array) {
+        int offset = 0;
+        int index = 0;
+        for (Node n : array) {
+            if (n.mCachedAddress != offset) {
+                throw new RuntimeException("Wrong address for node " + index
+                        + " : expected " + offset + ", got " + n.mCachedAddress);
+            }
+            ++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(byte[] buffer, int index, 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");
+        }
+    }
+
+    private static byte makeCharGroupFlags(final CharGroup group, final int groupAddress,
+            final int childrenOffset) {
+        byte flags = 0;
+        if (group.mChars.length > 1) flags |= FLAG_HAS_MULTIPLE_CHARS;
+        if (group.mFrequency >= 0) {
+            flags |= FLAG_IS_TERMINAL;
+        }
+        if (null != group.mChildren) {
+            switch (getByteSize(childrenOffset)) {
+             case 1:
+                 flags |= FLAG_GROUP_ADDRESS_TYPE_ONEBYTE;
+                 break;
+             case 2:
+                 flags |= FLAG_GROUP_ADDRESS_TYPE_TWOBYTES;
+                 break;
+             case 3:
+                 flags |= FLAG_GROUP_ADDRESS_TYPE_THREEBYTES;
+                 break;
+             default:
+                 throw new RuntimeException("Node with a strange address");
+             }
+        }
+        if (null != group.mShortcutTargets) {
+            if (0 == group.mShortcutTargets.size()) {
+                throw new RuntimeException("0-sized shortcut list must be null");
+            }
+            flags |= FLAG_HAS_SHORTCUT_TARGETS;
+        }
+        if (null != group.mBigrams) {
+            if (0 == group.mBigrams.size()) {
+                throw new RuntimeException("0-sized bigram list must be null");
+            }
+            flags |= FLAG_HAS_BIGRAMS;
+        }
+        if (group.mIsShortcutOnly) {
+            flags |= FLAG_IS_SHORTCUT_ONLY;
+        }
+        return flags;
+    }
+
+    /**
+     * Makes the flag value for an attribute.
+     *
+     * @param more whether there are more attributes after this one.
+     * @param offset the offset of the attribute.
+     * @param frequency the frequency of the attribute, 0..15
+     * @return the flags
+     */
+    private static final int makeAttributeFlags(final boolean more, final int offset,
+            final int frequency) {
+        int bigramFlags = (more ? FLAG_ATTRIBUTE_HAS_NEXT : 0)
+                + (offset < 0 ? FLAG_ATTRIBUTE_OFFSET_NEGATIVE : 0);
+        switch (getByteSize(offset)) {
+        case 1:
+            bigramFlags |= FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE;
+            break;
+        case 2:
+            bigramFlags |= FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES;
+            break;
+        case 3:
+            bigramFlags |= FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES;
+            break;
+        default:
+            throw new RuntimeException("Strange offset size");
+        }
+        bigramFlags += frequency & FLAG_ATTRIBUTE_FREQUENCY;
+        return bigramFlags;
+    }
+
+    /**
+     * 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.
+     * @return the address of the END of the node.
+     */
+    private static int writePlacedNode(FusionDictionary dict, byte[] buffer, Node node) {
+        int index = node.mCachedAddress;
+
+        final int groupCount = node.mData.size();
+        final int countSize = getGroupCountSize(node);
+        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) {
+            CharGroup group = node.mData.get(i);
+            if (index != group.mCachedAddress) throw new RuntimeException("Bug: write index is not "
+                    + "the same as the cached address of the group");
+            groupAddress += GROUP_FLAGS_SIZE + getGroupCharactersSize(group);
+            // Sanity checks.
+            if (group.mFrequency > MAX_TERMINAL_FREQUENCY) {
+                throw new RuntimeException("A node has a frequency > " + MAX_TERMINAL_FREQUENCY
+                        + " : " + group.mFrequency);
+            }
+            if (group.mFrequency >= 0) groupAddress += GROUP_FREQUENCY_SIZE;
+            final int childrenOffset = null == group.mChildren
+                    ? NO_CHILDREN_ADDRESS : group.mChildren.mCachedAddress - groupAddress;
+            byte flags = makeCharGroupFlags(group, groupAddress, childrenOffset);
+            buffer[index++] = flags;
+            index = CharEncoding.writeCharArray(group.mChars, buffer, index);
+            if (group.hasSeveralChars()) {
+                buffer[index++] = GROUP_CHARACTERS_TERMINATOR;
+            }
+            if (group.mFrequency >= 0) {
+                buffer[index++] = (byte) group.mFrequency;
+            }
+            final int shift = writeVariableAddress(buffer, index, childrenOffset);
+            index += shift;
+            groupAddress += shift;
+
+            // Write shortcuts
+            if (null != group.mShortcutTargets) {
+                final Iterator shortcutIterator = group.mShortcutTargets.iterator();
+                while (shortcutIterator.hasNext()) {
+                    final WeightedString target = (WeightedString)shortcutIterator.next();
+                    final int addressOfTarget = findAddressOfWord(dict, target.mWord);
+                    ++groupAddress;
+                    final int offset = addressOfTarget - groupAddress;
+                    int shortcutFlags = makeAttributeFlags(shortcutIterator.hasNext(), offset,
+                            target.mFrequency);
+                    buffer[index++] = (byte)shortcutFlags;
+                    final int shortcutShift = writeVariableAddress(buffer, index, Math.abs(offset));
+                    index += shortcutShift;
+                    groupAddress += shortcutShift;
+                }
+            }
+            // Write bigrams
+            if (null != group.mBigrams) {
+                final Iterator bigramIterator = group.mBigrams.iterator();
+                while (bigramIterator.hasNext()) {
+                    final WeightedString bigram = (WeightedString)bigramIterator.next();
+                    final int addressOfBigram = findAddressOfWord(dict, bigram.mWord);
+                    ++groupAddress;
+                    final int offset = addressOfBigram - groupAddress;
+                    int bigramFlags = makeAttributeFlags(bigramIterator.hasNext(), offset,
+                            bigram.mFrequency);
+                    buffer[index++] = (byte)bigramFlags;
+                    final int bigramShift = writeVariableAddress(buffer, index, Math.abs(offset));
+                    index += bigramShift;
+                    groupAddress += bigramShift;
+                }
+            }
+
+        }
+        if (index != node.mCachedAddress + node.mCachedSize) throw new RuntimeException(
+                "Not the same size : written "
+                + (index - node.mCachedAddress) + " bytes out of 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 (Node n : nodes) {
+            if (maxGroups < n.mData.size()) maxGroups = n.mData.size();
+            for (CharGroup cg : n.mData) {
+                ++charGroups;
+                if (cg.mChars.length > maxRuns) maxRuns = cg.mChars.length;
+                if (cg.mFrequency >= 0) {
+                    if (n.mCachedAddress < firstTerminalAddress)
+                        firstTerminalAddress = n.mCachedAddress;
+                    if (n.mCachedAddress > lastTerminalAddress)
+                        lastTerminalAddress = n.mCachedAddress;
+                }
+            }
+            if (n.mCachedAddress + n.mCachedSize > size) size = n.mCachedAddress + n.mCachedSize;
+        }
+        final int[] groupCounts = new int[maxGroups + 1];
+        final int[] runCounts = new int[maxRuns + 1];
+        for (Node n : nodes) {
+            ++groupCounts[n.mData.size()];
+            for (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 version the version of the format to write, currently either 1 or 2.
+     */
+    public static void writeDictionaryBinary(final OutputStream destination,
+            final FusionDictionary dict, final int version)
+            throws IOException, UnsupportedFormatException {
+
+        // Addresses are limited to 3 bytes, so we'll just make a 16MB buffer. Since addresses
+        // can be relative to each node, the structure itself is not limited to 16MB at all, but
+        // I doubt this will ever be shot. If it is, 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.
+        // Anyway, to make a dictionary bigger than 16MB just increase the size of this buffer.
+        final byte[] buffer = new byte[1 << 24];
+        int index = 0;
+
+        if (version < MINIMUM_SUPPORTED_VERSION || version > MAXIMUM_SUPPORTED_VERSION) {
+            throw new UnsupportedFormatException("Requested file format version " + version
+                    + ", but this implementation only supports versions "
+                    + MINIMUM_SUPPORTED_VERSION + " through " + MAXIMUM_SUPPORTED_VERSION);
+        }
+
+        // The magic number in big-endian order.
+        if (version >= FIRST_VERSION_WITH_HEADER_SIZE) {
+            // Magic number for version 2+.
+            buffer[index++] = (byte) (0xFF & (VERSION_2_MAGIC_NUMBER >> 24));
+            buffer[index++] = (byte) (0xFF & (VERSION_2_MAGIC_NUMBER >> 16));
+            buffer[index++] = (byte) (0xFF & (VERSION_2_MAGIC_NUMBER >> 8));
+            buffer[index++] = (byte) (0xFF & VERSION_2_MAGIC_NUMBER);
+            // Dictionary version.
+            buffer[index++] = (byte) (0xFF & (version >> 8));
+            buffer[index++] = (byte) (0xFF & version);
+        } else {
+            // Magic number for version 1.
+            buffer[index++] = (byte) (0xFF & (VERSION_1_MAGIC_NUMBER >> 8));
+            buffer[index++] = (byte) (0xFF & VERSION_1_MAGIC_NUMBER);
+            // Dictionary version.
+            buffer[index++] = (byte) (0xFF & version);
+        }
+        // Options flags
+        buffer[index++] = (byte) (0xFF & (OPTIONS >> 8));
+        buffer[index++] = (byte) (0xFF & OPTIONS);
+        if (version >= FIRST_VERSION_WITH_HEADER_SIZE) {
+            final int headerSizeOffset = index;
+            index += 4; // Size of the header size
+            // TODO: Write out the header contents here.
+            // Write out the header size.
+            buffer[headerSizeOffset] = (byte) (0xFF & (index >> 24));
+            buffer[headerSizeOffset + 1] = (byte) (0xFF & (index >> 16));
+            buffer[headerSizeOffset + 2] = (byte) (0xFF & (index >> 8));
+            buffer[headerSizeOffset + 3] = (byte) (0xFF & (index >> 0));
+        }
+
+        destination.write(buffer, 0, index);
+        index = 0;
+
+        // 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);
+        MakedictLog.i("Checking array...");
+        checkFlatNodeArray(flatNodes);
+
+        MakedictLog.i("Writing file...");
+        int dataEndOffset = 0;
+        for (Node n : flatNodes) {
+            dataEndOffset = writePlacedNode(dict, buffer, n);
+        }
+
+        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 final int[] characterBuffer = new int[MAX_WORD_LENGTH];
+    private static CharGroupInfo readCharGroup(RandomAccessFile source,
+            final int originalGroupAddress) throws IOException {
+        int addressPointer = originalGroupAddress;
+        final int flags = source.readUnsignedByte();
+        ++addressPointer;
+        final int characters[];
+        if (0 != (flags & FLAG_HAS_MULTIPLE_CHARS)) {
+            int index = 0;
+            int character = CharEncoding.readChar(source);
+            addressPointer += CharEncoding.getCharSize(character);
+            while (-1 != character) {
+                characterBuffer[index++] = character;
+                character = CharEncoding.readChar(source);
+                addressPointer += CharEncoding.getCharSize(character);
+            }
+            characters = Arrays.copyOfRange(characterBuffer, 0, index);
+        } else {
+            final int character = CharEncoding.readChar(source);
+            addressPointer += CharEncoding.getCharSize(character);
+            characters = new int[] { character };
+        }
+        final int frequency;
+        if (0 != (FLAG_IS_TERMINAL & flags)) {
+            ++addressPointer;
+            frequency = source.readUnsignedByte();
+        } else {
+            frequency = CharGroup.NOT_A_TERMINAL;
+        }
+        int childrenAddress = addressPointer;
+        switch (flags & MASK_GROUP_ADDRESS_TYPE) {
+        case FLAG_GROUP_ADDRESS_TYPE_ONEBYTE:
+            childrenAddress += source.readUnsignedByte();
+            addressPointer += 1;
+            break;
+        case FLAG_GROUP_ADDRESS_TYPE_TWOBYTES:
+            childrenAddress += source.readUnsignedShort();
+            addressPointer += 2;
+            break;
+        case FLAG_GROUP_ADDRESS_TYPE_THREEBYTES:
+            childrenAddress += (source.readUnsignedByte() << 16) + source.readUnsignedShort();
+            addressPointer += 3;
+            break;
+        case FLAG_GROUP_ADDRESS_TYPE_NOADDRESS:
+        default:
+            childrenAddress = NO_CHILDREN_ADDRESS;
+            break;
+        }
+        ArrayList<PendingAttribute> shortcutTargets = null;
+        if (0 != (flags & FLAG_HAS_SHORTCUT_TARGETS)) {
+            shortcutTargets = new ArrayList<PendingAttribute>();
+            while (true) {
+                final int targetFlags = source.readUnsignedByte();
+                ++addressPointer;
+                final int sign = 0 == (targetFlags & FLAG_ATTRIBUTE_OFFSET_NEGATIVE) ? 1 : -1;
+                int targetAddress = addressPointer;
+                switch (targetFlags & MASK_ATTRIBUTE_ADDRESS_TYPE) {
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
+                    targetAddress += sign * source.readUnsignedByte();
+                    addressPointer += 1;
+                    break;
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
+                    targetAddress += sign * source.readUnsignedShort();
+                    addressPointer += 2;
+                    break;
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
+                    final int offset = ((source.readUnsignedByte() << 16)
+                            + source.readUnsignedShort());
+                    targetAddress += sign * offset;
+                    addressPointer += 3;
+                    break;
+                default:
+                    throw new RuntimeException("Has shortcut targets with no address");
+                }
+                shortcutTargets.add(new PendingAttribute(targetFlags & FLAG_ATTRIBUTE_FREQUENCY,
+                        targetAddress));
+                if (0 == (targetFlags & FLAG_ATTRIBUTE_HAS_NEXT)) break;
+            }
+        }
+        ArrayList<PendingAttribute> bigrams = null;
+        if (0 != (flags & FLAG_HAS_BIGRAMS)) {
+            bigrams = new ArrayList<PendingAttribute>();
+            while (true) {
+                final int bigramFlags = source.readUnsignedByte();
+                ++addressPointer;
+                final int sign = 0 == (bigramFlags & FLAG_ATTRIBUTE_OFFSET_NEGATIVE) ? 1 : -1;
+                int bigramAddress = addressPointer;
+                switch (bigramFlags & MASK_ATTRIBUTE_ADDRESS_TYPE) {
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_ONEBYTE:
+                    bigramAddress += sign * source.readUnsignedByte();
+                    addressPointer += 1;
+                    break;
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_TWOBYTES:
+                    bigramAddress += sign * source.readUnsignedShort();
+                    addressPointer += 2;
+                    break;
+                case FLAG_ATTRIBUTE_ADDRESS_TYPE_THREEBYTES:
+                    final int offset = ((source.readUnsignedByte() << 16)
+                            + source.readUnsignedShort());
+                    bigramAddress += sign * offset;
+                    addressPointer += 3;
+                    break;
+                default:
+                    throw new RuntimeException("Has bigrams with no address");
+                }
+                bigrams.add(new PendingAttribute(bigramFlags & FLAG_ATTRIBUTE_FREQUENCY,
+                        bigramAddress));
+                if (0 == (bigramFlags & FLAG_ATTRIBUTE_HAS_NEXT)) break;
+            }
+        }
+        return new CharGroupInfo(originalGroupAddress, addressPointer, flags, characters, frequency,
+                childrenAddress, shortcutTargets, bigrams);
+    }
+
+    /**
+     * Reads and returns the char group count out of a file and forwards the pointer.
+     */
+    private static int readCharGroupCount(RandomAccessFile source) throws IOException {
+        final int msb = source.readUnsignedByte();
+        if (MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT >= msb) {
+            return msb;
+        } else {
+            return ((MAX_CHARGROUPS_FOR_ONE_BYTE_CHARGROUP_COUNT & msb) << 8)
+                    + source.readUnsignedByte();
+        }
+    }
+
+    /**
+     * Finds, as a string, the word at the address passed as an argument.
+     *
+     * @param source the file to read from.
+     * @param headerSize the size of the header.
+     * @param address the address to seek.
+     * @return the word, as a string.
+     * @throws IOException if the file can't be read.
+     */
+    private static String getWordAtAddress(RandomAccessFile source, long headerSize,
+            int address) throws IOException {
+        final long originalPointer = source.getFilePointer();
+        source.seek(headerSize);
+        final int count = readCharGroupCount(source);
+        int groupOffset = getGroupCountSize(count);
+        final StringBuilder builder = new StringBuilder();
+        String result = null;
+
+        CharGroupInfo last = null;
+        for (int i = count - 1; i >= 0; --i) {
+            CharGroupInfo info = readCharGroup(source, groupOffset);
+            groupOffset = info.mEndAddress;
+            if (info.mOriginalAddress == address) {
+                builder.append(new String(info.mCharacters, 0, info.mCharacters.length));
+                result = builder.toString();
+                break; // and return
+            }
+            if (hasChildrenAddress(info.mChildrenAddress)) {
+                if (info.mChildrenAddress > address) {
+                    if (null == last) continue;
+                    builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
+                    source.seek(last.mChildrenAddress + headerSize);
+                    groupOffset = last.mChildrenAddress + 1;
+                    i = source.readUnsignedByte();
+                    last = null;
+                    continue;
+                }
+                last = info;
+            }
+            if (0 == i && hasChildrenAddress(last.mChildrenAddress)) {
+                builder.append(new String(last.mCharacters, 0, last.mCharacters.length));
+                source.seek(last.mChildrenAddress + headerSize);
+                groupOffset = last.mChildrenAddress + 1;
+                i = source.readUnsignedByte();
+                last = null;
+                continue;
+            }
+        }
+        source.seek(originalPointer);
+        return result;
+    }
+
+    /**
+     * Reads a single node from a binary file.
+     *
+     * This methods reads the file at the current position of its file pointer. 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 source the data file, 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.
+     * @return the read node with all his children already read.
+     */
+    private static Node readNode(RandomAccessFile source, long headerSize,
+            Map<Integer, Node> reverseNodeMap, Map<Integer, CharGroup> reverseGroupMap)
+            throws IOException {
+        final int nodeOrigin = (int)(source.getFilePointer() - headerSize);
+        final int count = readCharGroupCount(source);
+        final ArrayList<CharGroup> nodeContents = new ArrayList<CharGroup>();
+        int groupOffset = nodeOrigin + getGroupCountSize(count);
+        for (int i = count; i > 0; --i) {
+            CharGroupInfo info = readCharGroup(source, groupOffset);
+            ArrayList<WeightedString> shortcutTargets = null;
+            if (null != info.mShortcutTargets) {
+                shortcutTargets = new ArrayList<WeightedString>();
+                for (PendingAttribute target : info.mShortcutTargets) {
+                    final String word = getWordAtAddress(source, headerSize, target.mAddress);
+                    shortcutTargets.add(new WeightedString(word, target.mFrequency));
+                }
+            }
+            ArrayList<WeightedString> bigrams = null;
+            if (null != info.mBigrams) {
+                bigrams = new ArrayList<WeightedString>();
+                for (PendingAttribute bigram : info.mBigrams) {
+                    final String word = getWordAtAddress(source, headerSize, bigram.mAddress);
+                    bigrams.add(new WeightedString(word, bigram.mFrequency));
+                }
+            }
+            if (hasChildrenAddress(info.mChildrenAddress)) {
+                Node children = reverseNodeMap.get(info.mChildrenAddress);
+                if (null == children) {
+                    final long currentPosition = source.getFilePointer();
+                    source.seek(info.mChildrenAddress + headerSize);
+                    children = readNode(source, headerSize, reverseNodeMap, reverseGroupMap);
+                    source.seek(currentPosition);
+                }
+                nodeContents.add(
+                        new CharGroup(info.mCharacters, shortcutTargets, bigrams, info.mFrequency,
+                                children, isShortcutOnly(info)));
+            } else {
+                nodeContents.add(
+                        new CharGroup(info.mCharacters, shortcutTargets, bigrams, info.mFrequency,
+                                isShortcutOnly(info)));
+            }
+            groupOffset = info.mEndAddress;
+        }
+        final Node node = new Node(nodeContents);
+        node.mCachedAddress = nodeOrigin;
+        reverseNodeMap.put(node.mCachedAddress, node);
+        return node;
+    }
+
+    /**
+     * Helper function to get the binary format version from the header.
+     */
+    private static int getFormatVersion(final RandomAccessFile source) throws IOException {
+        final int magic_v1 = source.readUnsignedShort();
+        if (VERSION_1_MAGIC_NUMBER == magic_v1) return source.readUnsignedByte();
+        final int magic_v2 = (magic_v1 << 16) + source.readUnsignedShort();
+        if (VERSION_2_MAGIC_NUMBER == magic_v2) return source.readUnsignedShort();
+        return NOT_A_VERSION_NUMBER;
+    }
+
+    /**
+     * Reads a random access file and returns the memory representation of the dictionary.
+     *
+     * This high-level method takes a binary file and reads its contents, populating a
+     * FusionDictionary structure. The optional dict argument is an existing dictionary to
+     * which words from the file should be added. If it is null, a new dictionary is created.
+     *
+     * @param source the file to read.
+     * @param dict an optional dictionary to add words to, or null.
+     * @return the created (or merged) dictionary.
+     */
+    public static FusionDictionary readDictionaryBinary(final RandomAccessFile source,
+            final FusionDictionary dict) throws IOException, UnsupportedFormatException {
+        // Check file version
+        final int version = getFormatVersion(source);
+        if (version < MINIMUM_SUPPORTED_VERSION || version > MAXIMUM_SUPPORTED_VERSION ) {
+            throw new UnsupportedFormatException("This file has version " + version
+                    + ", but this implementation does not support versions above "
+                    + MAXIMUM_SUPPORTED_VERSION);
+        }
+
+        // Read options
+        source.readUnsignedShort();
+
+        final long headerSize;
+        if (version < FIRST_VERSION_WITH_HEADER_SIZE) {
+            headerSize = source.getFilePointer();
+        } else {
+            headerSize = (source.readUnsignedByte() << 24) + (source.readUnsignedByte() << 16)
+                    + (source.readUnsignedByte() << 8) + source.readUnsignedByte();
+            // read the header body
+            source.seek(headerSize);
+        }
+
+        Map<Integer, Node> reverseNodeMapping = new TreeMap<Integer, Node>();
+        Map<Integer, CharGroup> reverseGroupMapping = new TreeMap<Integer, CharGroup>();
+        final Node root = readNode(source, headerSize, reverseNodeMapping, reverseGroupMapping);
+
+        FusionDictionary newDict = new FusionDictionary(root,
+                new FusionDictionary.DictionaryOptions());
+        if (null != dict) {
+            for (Word w : dict) {
+                newDict.add(w.mWord, w.mFrequency, w.mShortcutTargets, w.mBigrams);
+            }
+        }
+
+        return newDict;
+    }
+
+    /**
+     * Basic test to find out whether the file is a binary dictionary or not.
+     *
+     * Concretely this only tests the magic number.
+     *
+     * @param filename The name of the file to test.
+     * @return true if it's a binary dictionary, false otherwise
+     */
+    public static boolean isBinaryDictionary(final String filename) {
+        try {
+            RandomAccessFile f = new RandomAccessFile(filename, "r");
+            final int version = getFormatVersion(f);
+            return (version >= MINIMUM_SUPPORTED_VERSION && version <= MAXIMUM_SUPPORTED_VERSION);
+        } catch (FileNotFoundException e) {
+            return false;
+        } catch (IOException e) {
+            return false;
+        }
+    }
+}