Move code only used for dicttool and tests under tests.

Bug: 13035567
Change-Id: I13c6df013ef2b67c9bf67455d9c32d283bf9ea2e

1 files changed, 881 insertions, 0 deletions

diff --git a/tests/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
new file mode 100644
index 000000000..39bd98bad
--- /dev/null
+++ b/tests/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
@@ -0,0 +1,881 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.inputmethod.latin.makedict;
+
+import com.android.inputmethod.annotations.UsedForTesting;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.CharEncoding;
+import com.android.inputmethod.latin.makedict.BinaryDictDecoderUtils.DictBuffer;
+import com.android.inputmethod.latin.makedict.FormatSpec.FormatOptions;
+import com.android.inputmethod.latin.makedict.FusionDictionary.PtNode;
+import com.android.inputmethod.latin.makedict.FusionDictionary.PtNodeArray;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.util.ArrayList;
+
+/**
+ * Encodes binary files for a FusionDictionary.
+ *
+ * All the methods in this class are static.
+ *
+ * TODO: Rename this class to DictEncoderUtils.
+ */
+public class BinaryDictEncoderUtils {
+
+    private static final boolean DBG = MakedictLog.DBG;
+
+    private BinaryDictEncoderUtils() {
+        // This utility class is not publicly instantiable.
+    }
+
+    // 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;
+
+    /**
+     * 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 getPtNodeCharactersSize(final int[] characters) {
+        int size = CharEncoding.getCharArraySize(characters);
+        if (characters.length > 1) size += FormatSpec.PTNODE_TERMINATOR_SIZE;
+        return size;
+    }
+
+    /**
+     * Compute the binary size of the character array in a PtNode
+     *
+     * 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 ptNode the PtNode
+     * @return the size of the char array, including the terminator if any
+     */
+    private static int getPtNodeCharactersSize(final PtNode ptNode) {
+        return getPtNodeCharactersSize(ptNode.mChars);
+    }
+
+    /**
+     * Compute the binary size of the PtNode count for a node array.
+     * @param nodeArray the nodeArray
+     * @return the size of the PtNode count, either 1 or 2 bytes.
+     */
+    private static int getPtNodeCountSize(final PtNodeArray nodeArray) {
+        return BinaryDictIOUtils.getPtNodeCountSize(nodeArray.mData.size());
+    }
+
+    /**
+     * Compute the size of a shortcut in bytes.
+     */
+    private static int getShortcutSize(final WeightedString shortcut) {
+        int size = FormatSpec.PTNODE_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.PTNODE_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 || shortcutList.isEmpty()) return 0;
+        int size = FormatSpec.PTNODE_SHORTCUT_LIST_SIZE_SIZE;
+        for (final WeightedString shortcut : shortcutList) {
+            size += getShortcutSize(shortcut);
+        }
+        return size;
+    }
+
+    /**
+     * Compute the maximum size of a PtNode, assuming 3-byte addresses for everything.
+     *
+     * @param ptNode the PtNode to compute the size of.
+     * @return the maximum size of the PtNode.
+     */
+    private static int getPtNodeMaximumSize(final PtNode ptNode) {
+        int size = getNodeHeaderSize(ptNode);
+        if (ptNode.isTerminal()) {
+            // If terminal, one byte for the frequency.
+            size += FormatSpec.PTNODE_FREQUENCY_SIZE;
+        }
+        size += FormatSpec.PTNODE_MAX_ADDRESS_SIZE; // For children address
+        size += getShortcutListSize(ptNode.mShortcutTargets);
+        if (null != ptNode.mBigrams) {
+            size += (FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE
+                    + FormatSpec.PTNODE_ATTRIBUTE_MAX_ADDRESS_SIZE)
+                    * ptNode.mBigrams.size();
+        }
+        return size;
+    }
+
+    /**
+     * Compute the maximum size of each PtNode of a PtNode array, assuming 3-byte addresses for
+     * everything, and caches it in the `mCachedSize' member of the nodes; deduce the size of
+     * the containing node array, and cache it it its 'mCachedSize' member.
+     *
+     * @param ptNodeArray the node array to compute the maximum size of.
+     */
+    private static void calculatePtNodeArrayMaximumSize(final PtNodeArray ptNodeArray) {
+        int size = getPtNodeCountSize(ptNodeArray);
+        for (PtNode node : ptNodeArray.mData) {
+            final int nodeSize = getPtNodeMaximumSize(node);
+            node.mCachedSize = nodeSize;
+            size += nodeSize;
+        }
+        ptNodeArray.mCachedSize = size;
+    }
+
+    /**
+     * Compute the size of the header (flag + [parent address] + characters size) of a PtNode.
+     *
+     * @param ptNode the PtNode of which to compute the size of the header
+     */
+    private static int getNodeHeaderSize(final PtNode ptNode) {
+        return FormatSpec.PTNODE_FLAGS_SIZE + getPtNodeCharactersSize(ptNode);
+    }
+
+    /**
+     * 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;
+        }
+    }
+
+    static int writeUIntToBuffer(final byte[] buffer, int position, final int value,
+            final int size) {
+        switch(size) {
+            case 4:
+                buffer[position++] = (byte) ((value >> 24) & 0xFF);
+                /* fall through */
+            case 3:
+                buffer[position++] = (byte) ((value >> 16) & 0xFF);
+                /* fall through */
+            case 2:
+                buffer[position++] = (byte) ((value >> 8) & 0xFF);
+                /* fall through */
+            case 1:
+                buffer[position++] = (byte) (value & 0xFF);
+                break;
+            default:
+                /* nop */
+        }
+        return position;
+    }
+
+    static void writeUIntToStream(final OutputStream stream, final int value, final int size)
+            throws IOException {
+        switch(size) {
+            case 4:
+                stream.write((value >> 24) & 0xFF);
+                /* fall through */
+            case 3:
+                stream.write((value >> 16) & 0xFF);
+                /* fall through */
+            case 2:
+                stream.write((value >> 8) & 0xFF);
+                /* fall through */
+            case 1:
+                stream.write(value & 0xFF);
+                break;
+            default:
+                /* nop */
+        }
+    }
+
+    @UsedForTesting
+    static void writeUIntToDictBuffer(final DictBuffer dictBuffer, final int value,
+            final int size) {
+        switch(size) {
+            case 4:
+                dictBuffer.put((byte) ((value >> 24) & 0xFF));
+                /* fall through */
+            case 3:
+                dictBuffer.put((byte) ((value >> 16) & 0xFF));
+                /* fall through */
+            case 2:
+                dictBuffer.put((byte) ((value >> 8) & 0xFF));
+                /* fall through */
+            case 1:
+                dictBuffer.put((byte) (value & 0xFF));
+                break;
+            default:
+                /* nop */
+        }
+    }
+
+    // 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<PtNodeArray> flattenTree(
+            final PtNodeArray rootNodeArray) {
+        final int treeSize = FusionDictionary.countPtNodes(rootNodeArray);
+        MakedictLog.i("Counted nodes : " + treeSize);
+        final ArrayList<PtNodeArray> flatTree = new ArrayList<PtNodeArray>(treeSize);
+        return flattenTreeInner(flatTree, rootNodeArray);
+    }
+
+    private static ArrayList<PtNodeArray> flattenTreeInner(final ArrayList<PtNodeArray> list,
+            final PtNodeArray ptNodeArray) {
+        // 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(ptNodeArray);
+        final ArrayList<PtNode> branches = ptNodeArray.mData;
+        for (PtNode ptNode : branches) {
+            if (null != ptNode.mChildren) flattenTreeInner(list, ptNode.mChildren);
+        }
+        return list;
+    }
+
+    /**
+     * Get the offset from a position inside a current node array to a target node array, during
+     * update.
+     *
+     * If the current node array is before the target node array, the target node array has not
+     * been updated yet, so we should return the offset from the old position of the current node
+     * array to the old position of the target node array. If on the other hand the target is
+     * before the current node array, it already has been updated, so we should return the offset
+     * from the new position in the current node array to the new position in the target node
+     * array.
+     *
+     * @param currentNodeArray node array containing the PtNode where the offset will be written
+     * @param offsetFromStartOfCurrentNodeArray offset, in bytes, from the start of currentNodeArray
+     * @param targetNodeArray the target node array to get the offset to
+     * @return the offset to the target node array
+     */
+    private static int getOffsetToTargetNodeArrayDuringUpdate(final PtNodeArray currentNodeArray,
+            final int offsetFromStartOfCurrentNodeArray, final PtNodeArray targetNodeArray) {
+        final boolean isTargetBeforeCurrent = (targetNodeArray.mCachedAddressBeforeUpdate
+                < currentNodeArray.mCachedAddressBeforeUpdate);
+        if (isTargetBeforeCurrent) {
+            return targetNodeArray.mCachedAddressAfterUpdate
+                    - (currentNodeArray.mCachedAddressAfterUpdate
+                            + offsetFromStartOfCurrentNodeArray);
+        } else {
+            return targetNodeArray.mCachedAddressBeforeUpdate
+                    - (currentNodeArray.mCachedAddressBeforeUpdate
+                            + offsetFromStartOfCurrentNodeArray);
+        }
+    }
+
+    /**
+     * Get the offset from a position inside a current node array to a target PtNode, during
+     * update.
+     *
+     * @param currentNodeArray node array containing the PtNode where the offset will be written
+     * @param offsetFromStartOfCurrentNodeArray offset, in bytes, from the start of currentNodeArray
+     * @param targetPtNode the target PtNode to get the offset to
+     * @return the offset to the target PtNode
+     */
+    // TODO: is there any way to factorize this method with the one above?
+    private static int getOffsetToTargetPtNodeDuringUpdate(final PtNodeArray currentNodeArray,
+            final int offsetFromStartOfCurrentNodeArray, final PtNode targetPtNode) {
+        final int oldOffsetBasePoint = currentNodeArray.mCachedAddressBeforeUpdate
+                + offsetFromStartOfCurrentNodeArray;
+        final boolean isTargetBeforeCurrent = (targetPtNode.mCachedAddressBeforeUpdate
+                < oldOffsetBasePoint);
+        // If the target is before the current node array, 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 = currentNodeArray.mCachedAddressAfterUpdate
+                    + offsetFromStartOfCurrentNodeArray;
+            return targetPtNode.mCachedAddressAfterUpdate - newOffsetBasePoint;
+        } else {
+            return targetPtNode.mCachedAddressBeforeUpdate - oldOffsetBasePoint;
+        }
+    }
+
+    /**
+     * Computes the actual node array size, based on the cached addresses of the children nodes.
+     *
+     * Each node array stores its tentative address. During dictionary address computing, these
+     * are not final, but they can be used to compute the node array size (the node array 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 array
+     * contents (as in, any of the addresses stored in the cache fields) have changed with
+     * respect to their previous value.
+     *
+     * @param ptNodeArray the node array to compute the size of.
+     * @param dict the dictionary in which the word/attributes are to be found.
+     * @return false if none of the cached addresses inside the node array changed, true otherwise.
+     */
+    private static boolean computeActualPtNodeArraySize(final PtNodeArray ptNodeArray,
+            final FusionDictionary dict) {
+        boolean changed = false;
+        int size = getPtNodeCountSize(ptNodeArray);
+        for (PtNode ptNode : ptNodeArray.mData) {
+            ptNode.mCachedAddressAfterUpdate = ptNodeArray.mCachedAddressAfterUpdate + size;
+            if (ptNode.mCachedAddressAfterUpdate != ptNode.mCachedAddressBeforeUpdate) {
+                changed = true;
+            }
+            int nodeSize = getNodeHeaderSize(ptNode);
+            if (ptNode.isTerminal()) {
+                nodeSize += FormatSpec.PTNODE_FREQUENCY_SIZE;
+            }
+            if (null != ptNode.mChildren) {
+                nodeSize += getByteSize(getOffsetToTargetNodeArrayDuringUpdate(ptNodeArray,
+                        nodeSize + size, ptNode.mChildren));
+            }
+            nodeSize += getShortcutListSize(ptNode.mShortcutTargets);
+            if (null != ptNode.mBigrams) {
+                for (WeightedString bigram : ptNode.mBigrams) {
+                    final int offset = getOffsetToTargetPtNodeDuringUpdate(ptNodeArray,
+                            nodeSize + size + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE,
+                            FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord));
+                    nodeSize += getByteSize(offset) + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE;
+                }
+            }
+            ptNode.mCachedSize = nodeSize;
+            size += nodeSize;
+        }
+        if (ptNodeArray.mCachedSize != size) {
+            ptNodeArray.mCachedSize = size;
+            changed = true;
+        }
+        return changed;
+    }
+
+    /**
+     * Initializes the cached addresses of node arrays and their containing nodes from their size.
+     *
+     * @param flatNodes the list of node arrays.
+     * @return the byte size of the entire stack.
+     */
+    private static int initializePtNodeArraysCachedAddresses(
+            final ArrayList<PtNodeArray> flatNodes) {
+        int nodeArrayOffset = 0;
+        for (final PtNodeArray nodeArray : flatNodes) {
+            nodeArray.mCachedAddressBeforeUpdate = nodeArrayOffset;
+            int nodeCountSize = getPtNodeCountSize(nodeArray);
+            int nodeffset = 0;
+            for (final PtNode ptNode : nodeArray.mData) {
+                ptNode.mCachedAddressBeforeUpdate = ptNode.mCachedAddressAfterUpdate =
+                        nodeCountSize + nodeArrayOffset + nodeffset;
+                nodeffset += ptNode.mCachedSize;
+            }
+            nodeArrayOffset += nodeArray.mCachedSize;
+        }
+        return nodeArrayOffset;
+    }
+
+    /**
+     * Updates the cached addresses of node arrays after recomputing their new positions.
+     *
+     * @param flatNodes the list of node arrays.
+     */
+    private static void updatePtNodeArraysCachedAddresses(final ArrayList<PtNodeArray> flatNodes) {
+        for (final PtNodeArray nodeArray : flatNodes) {
+            nodeArray.mCachedAddressBeforeUpdate = nodeArray.mCachedAddressAfterUpdate;
+            for (final PtNode ptNode : nodeArray.mData) {
+                ptNode.mCachedAddressBeforeUpdate = ptNode.mCachedAddressAfterUpdate;
+            }
+        }
+    }
+
+    /**
+     * Compute the addresses and sizes of an ordered list of PtNode arrays.
+     *
+     * This method takes a list of PtNode arrays and will update their cached address and size
+     * values so that they can be written into a file. It determines the smallest size each of the
+     * PtNode arrays can be given the addresses of its children and attributes, and store that into
+     * each PtNode.
+     * The order of the PtNode 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 list of PtNode arrays
+     * @return the same array it was passed. The nodes have been updated for address and size.
+     */
+    /* package */ static ArrayList<PtNodeArray> computeAddresses(final FusionDictionary dict,
+            final ArrayList<PtNodeArray> flatNodes) {
+        // First get the worst possible sizes and offsets
+        for (final PtNodeArray n : flatNodes) {
+            calculatePtNodeArrayMaximumSize(n);
+        }
+        final int offset = initializePtNodeArraysCachedAddresses(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;
+            int ptNodeArrayStartOffset = 0;
+            for (final PtNodeArray ptNodeArray : flatNodes) {
+                ptNodeArray.mCachedAddressAfterUpdate = ptNodeArrayStartOffset;
+                final int oldNodeArraySize = ptNodeArray.mCachedSize;
+                final boolean changed = computeActualPtNodeArraySize(ptNodeArray, dict);
+                final int newNodeArraySize = ptNodeArray.mCachedSize;
+                if (oldNodeArraySize < newNodeArraySize) {
+                    throw new RuntimeException("Increased size ?!");
+                }
+                ptNodeArrayStartOffset += newNodeArraySize;
+                changesDone |= changed;
+            }
+            updatePtNodeArraysCachedAddresses(flatNodes);
+            ++passes;
+            if (passes > MAX_PASSES) throw new RuntimeException("Too many passes - probably a bug");
+        } while (changesDone);
+
+        final PtNodeArray lastPtNodeArray = flatNodes.get(flatNodes.size() - 1);
+        MakedictLog.i("Compression complete in " + passes + " passes.");
+        MakedictLog.i("After address compression : "
+                + (lastPtNodeArray.mCachedAddressAfterUpdate + lastPtNodeArray.mCachedSize));
+
+        return flatNodes;
+    }
+
+    /**
+     * Sanity-checking method.
+     *
+     * This method checks a list of PtNode arrays for juxtaposition, that is, it will do
+     * nothing if each node array's cached address is actually the previous node array's address
+     * plus the previous node's size.
+     * If this is not the case, it will throw an exception.
+     *
+     * @param arrays the list of node arrays to check
+     */
+    /* package */ static void checkFlatPtNodeArrayList(final ArrayList<PtNodeArray> arrays) {
+        int offset = 0;
+        int index = 0;
+        for (final PtNodeArray ptNodeArray : arrays) {
+            // BeforeUpdate and AfterUpdate addresses are the same here, so it does not matter
+            // which we use.
+            if (ptNodeArray.mCachedAddressAfterUpdate != offset) {
+                throw new RuntimeException("Wrong address for node " + index
+                        + " : expected " + offset + ", got " +
+                        ptNodeArray.mCachedAddressAfterUpdate);
+            }
+            ++index;
+            offset += ptNodeArray.mCachedSize;
+        }
+    }
+
+    /**
+     * Helper method to write a children position to a file.
+     *
+     * @param buffer the buffer to write to.
+     * @param index the index in the buffer to write the address to.
+     * @param position the position to write.
+     * @return the size in bytes the address actually took.
+     */
+    /* package */ static int writeChildrenPosition(final byte[] buffer, int index,
+            final int position) {
+        switch (getByteSize(position)) {
+        case 1:
+            buffer[index++] = (byte)position;
+            return 1;
+        case 2:
+            buffer[index++] = (byte)(0xFF & (position >> 8));
+            buffer[index++] = (byte)(0xFF & position);
+            return 2;
+        case 3:
+            buffer[index++] = (byte)(0xFF & (position >> 16));
+            buffer[index++] = (byte)(0xFF & (position >> 8));
+            buffer[index++] = (byte)(0xFF & position);
+            return 3;
+        case 0:
+            return 0;
+        default:
+            throw new RuntimeException("Position " + position + " has a strange size");
+        }
+    }
+
+    /**
+     * Helper method to write a signed children position to a file.
+     *
+     * @param buffer the buffer to write to.
+     * @param index the index in the buffer to write the address to.
+     * @param position the position to write.
+     * @return the size in bytes the address actually took.
+     */
+    /* package */ static int writeSignedChildrenPosition(final byte[] buffer, int index,
+            final int position) {
+        if (!BinaryDictIOUtils.hasChildrenAddress(position)) {
+            buffer[index] = buffer[index + 1] = buffer[index + 2] = 0;
+        } else {
+            final int absPosition = Math.abs(position);
+            buffer[index++] =
+                    (byte)((position < 0 ? FormatSpec.MSB8 : 0) | (0xFF & (absPosition >> 16)));
+            buffer[index++] = (byte)(0xFF & (absPosition >> 8));
+            buffer[index++] = (byte)(0xFF & absPosition);
+        }
+        return 3;
+    }
+
+    /**
+     * Makes the flag value for a PtNode.
+     *
+     * @param hasMultipleChars whether the PtNode has multiple chars.
+     * @param isTerminal whether the PtNode is terminal.
+     * @param childrenAddressSize the size of a children address.
+     * @param hasShortcuts whether the PtNode has shortcuts.
+     * @param hasBigrams whether the PtNode has bigrams.
+     * @param isNotAWord whether the PtNode is not a word.
+     * @param isBlackListEntry whether the PtNode is a blacklist entry.
+     * @return the flags
+     */
+    static int makePtNodeFlags(final boolean hasMultipleChars, final boolean isTerminal,
+            final int childrenAddressSize, final boolean hasShortcuts, final boolean hasBigrams,
+            final boolean isNotAWord, final boolean isBlackListEntry) {
+        byte flags = 0;
+        if (hasMultipleChars) flags |= FormatSpec.FLAG_HAS_MULTIPLE_CHARS;
+        if (isTerminal) flags |= FormatSpec.FLAG_IS_TERMINAL;
+        switch (childrenAddressSize) {
+            case 1:
+                flags |= FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_ONEBYTE;
+                break;
+            case 2:
+                flags |= FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_TWOBYTES;
+                break;
+            case 3:
+                flags |= FormatSpec.FLAG_CHILDREN_ADDRESS_TYPE_THREEBYTES;
+                break;
+            case 0:
+                flags |= FormatSpec.FLAG_CHILDREN_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;
+    }
+
+    /* package */ static byte makePtNodeFlags(final PtNode node, final int childrenOffset) {
+        return (byte) makePtNodeFlags(node.mChars.length > 1, node.isTerminal(),
+                getByteSize(childrenOffset),
+                node.mShortcutTargets != null && !node.mShortcutTargets.isEmpty(),
+                node.mBigrams != null && !node.mBigrams.isEmpty(),
+                node.mIsNotAWord, node.mIsBlacklistEntry);
+    }
+
+    /**
+     * 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
+     */
+    /* package */ static final int makeBigramFlags(final boolean more, final int offset,
+            int bigramFrequency, final int unigramFrequency, final String word) {
+        int bigramFlags = (more ? FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_HAS_NEXT : 0)
+                + (offset < 0 ? FormatSpec.FLAG_BIGRAM_ATTR_OFFSET_NEGATIVE : 0);
+        switch (getByteSize(offset)) {
+        case 1:
+            bigramFlags |= FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_ONEBYTE;
+            break;
+        case 2:
+            bigramFlags |= FormatSpec.FLAG_BIGRAM_ATTR_ADDRESS_TYPE_TWOBYTES;
+            break;
+        case 3:
+            bigramFlags |= FormatSpec.FLAG_BIGRAM_ATTR_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;
+        }
+        bigramFlags += getBigramFrequencyDiff(unigramFrequency, bigramFrequency)
+                & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY;
+        return bigramFlags;
+    }
+
+    public static int getBigramFrequencyDiff(final int unigramFrequency,
+            final int bigramFrequency) {
+        // 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.
+        return discretizedFrequency > 0 ? discretizedFrequency : 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_BIGRAM_SHORTCUT_ATTR_HAS_NEXT : 0)
+                + (frequency & FormatSpec.FLAG_BIGRAM_SHORTCUT_ATTR_FREQUENCY);
+    }
+
+    /* package */ static final int getChildrenPosition(final PtNode ptNode) {
+        int positionOfChildrenPosField = ptNode.mCachedAddressAfterUpdate
+                + getNodeHeaderSize(ptNode);
+        if (ptNode.isTerminal()) {
+            // A terminal node has the frequency.
+            // If positionOfChildrenPosField is incorrect, we may crash when jumping to the children
+            // position.
+            positionOfChildrenPosField += FormatSpec.PTNODE_FREQUENCY_SIZE;
+        }
+        return null == ptNode.mChildren ? FormatSpec.NO_CHILDREN_ADDRESS
+                : ptNode.mChildren.mCachedAddressAfterUpdate - positionOfChildrenPosField;
+    }
+
+    /**
+     * Write a PtNodeArray. The PtNodeArray is expected to have its final position cached.
+     *
+     * @param dict the dictionary the node array is a part of (for relative offsets).
+     * @param dictEncoder the dictionary encoder.
+     * @param ptNodeArray the node array to write.
+     */
+    @SuppressWarnings("unused")
+    /* package */ static void writePlacedPtNodeArray(final FusionDictionary dict,
+            final DictEncoder dictEncoder, final PtNodeArray ptNodeArray) {
+        // TODO: Make the code in common with BinaryDictIOUtils#writePtNode
+        dictEncoder.setPosition(ptNodeArray.mCachedAddressAfterUpdate);
+
+        final int ptNodeCount = ptNodeArray.mData.size();
+        dictEncoder.writePtNodeCount(ptNodeCount);
+        final int parentPosition =
+                (ptNodeArray.mCachedParentAddress == FormatSpec.NO_PARENT_ADDRESS)
+                ? FormatSpec.NO_PARENT_ADDRESS
+                : ptNodeArray.mCachedParentAddress + ptNodeArray.mCachedAddressAfterUpdate;
+        for (int i = 0; i < ptNodeCount; ++i) {
+            final PtNode ptNode = ptNodeArray.mData.get(i);
+            if (dictEncoder.getPosition() != ptNode.mCachedAddressAfterUpdate) {
+                throw new RuntimeException("Bug: write index is not the same as the cached address "
+                        + "of the node : " + dictEncoder.getPosition() + " <> "
+                        + ptNode.mCachedAddressAfterUpdate);
+            }
+            // Sanity checks.
+            if (DBG && ptNode.getProbability() > FormatSpec.MAX_TERMINAL_FREQUENCY) {
+                throw new RuntimeException("A node has a frequency > "
+                        + FormatSpec.MAX_TERMINAL_FREQUENCY
+                        + " : " + ptNode.mProbabilityInfo.toString());
+            }
+            dictEncoder.writePtNode(ptNode, dict);
+        }
+        if (dictEncoder.getPosition() != ptNodeArray.mCachedAddressAfterUpdate
+                + ptNodeArray.mCachedSize) {
+            throw new RuntimeException("Not the same size : written "
+                     + (dictEncoder.getPosition() - ptNodeArray.mCachedAddressAfterUpdate)
+                     + " bytes from a node that should have " + ptNodeArray.mCachedSize + " bytes");
+        }
+    }
+
+    /**
+     * Dumps a collection of useful statistics about a list of PtNode arrays.
+     *
+     * This prints purely informative stuff, like the total estimated file size, the
+     * number of PtNode arrays, of PtNodes, the repartition of each address size, etc
+     *
+     * @param ptNodeArrays the list of PtNode arrays.
+     */
+    /* package */ static void showStatistics(ArrayList<PtNodeArray> ptNodeArrays) {
+        int firstTerminalAddress = Integer.MAX_VALUE;
+        int lastTerminalAddress = Integer.MIN_VALUE;
+        int size = 0;
+        int ptNodes = 0;
+        int maxNodes = 0;
+        int maxRuns = 0;
+        for (final PtNodeArray ptNodeArray : ptNodeArrays) {
+            if (maxNodes < ptNodeArray.mData.size()) maxNodes = ptNodeArray.mData.size();
+            for (final PtNode ptNode : ptNodeArray.mData) {
+                ++ptNodes;
+                if (ptNode.mChars.length > maxRuns) maxRuns = ptNode.mChars.length;
+                if (ptNode.isTerminal()) {
+                    if (ptNodeArray.mCachedAddressAfterUpdate < firstTerminalAddress)
+                        firstTerminalAddress = ptNodeArray.mCachedAddressAfterUpdate;
+                    if (ptNodeArray.mCachedAddressAfterUpdate > lastTerminalAddress)
+                        lastTerminalAddress = ptNodeArray.mCachedAddressAfterUpdate;
+                }
+            }
+            if (ptNodeArray.mCachedAddressAfterUpdate + ptNodeArray.mCachedSize > size) {
+                size = ptNodeArray.mCachedAddressAfterUpdate + ptNodeArray.mCachedSize;
+            }
+        }
+        final int[] ptNodeCounts = new int[maxNodes + 1];
+        final int[] runCounts = new int[maxRuns + 1];
+        for (final PtNodeArray ptNodeArray : ptNodeArrays) {
+            ++ptNodeCounts[ptNodeArray.mData.size()];
+            for (final PtNode ptNode : ptNodeArray.mData) {
+                ++runCounts[ptNode.mChars.length];
+            }
+        }
+
+        MakedictLog.i("Statistics:\n"
+                + "  total file size " + size + "\n"
+                + "  " + ptNodeArrays.size() + " node arrays\n"
+                + "  " + ptNodes + " PtNodes (" + ((float)ptNodes / ptNodeArrays.size())
+                        + " PtNodes per node)\n"
+                + "  first terminal at " + firstTerminalAddress + "\n"
+                + "  last terminal at " + lastTerminalAddress + "\n"
+                + "  PtNode stats : max = " + maxNodes);
+        for (int i = 0; i < ptNodeCounts.length; ++i) {
+            MakedictLog.i("    " + i + " : " + ptNodeCounts[i]);
+        }
+        MakedictLog.i("  Character run stats : max = " + maxRuns);
+        for (int i = 0; i < runCounts.length; ++i) {
+            MakedictLog.i("    " + i + " : " + runCounts[i]);
+        }
+    }
+
+    /**
+     * Writes a file header to an output stream.
+     *
+     * @param destination the stream to write the file header to.
+     * @param dict the dictionary to write.
+     * @param formatOptions file format options.
+     * @return the size of the header.
+     */
+    /* package */ static int writeDictionaryHeader(final OutputStream destination,
+            final FusionDictionary dict, final FormatOptions formatOptions)
+                    throws IOException, UnsupportedFormatException {
+        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
+        // TODO: Remove this field.
+        final int options = 0;
+        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();
+        return size;
+    }
+}