Make PtNode have ProbabilityInfo instead of raw value.

Bug: 11281877
Bug: 12810574
Change-Id: Id1cda0afc74c4e30633c735729143491b2274a7b

11 files changed, 140 insertions, 104 deletions

diff --git a/java/src/com/android/inputmethod/latin/DictionaryWriter.java b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
index 84898680e..b931c66d1 100644
--- a/java/src/com/android/inputmethod/latin/DictionaryWriter.java
+++ b/java/src/com/android/inputmethod/latin/DictionaryWriter.java
@@ -21,6 +21,7 @@ import com.android.inputmethod.latin.makedict.FormatSpec;
 import com.android.inputmethod.latin.makedict.FusionDictionary;
 import com.android.inputmethod.latin.makedict.FusionDictionary.PtNodeArray;
 import com.android.inputmethod.latin.makedict.FusionDictionary.WeightedString;
+import com.android.inputmethod.latin.makedict.ProbabilityInfo;
 import com.android.inputmethod.latin.makedict.UnsupportedFormatException;
 import com.android.inputmethod.latin.utils.CollectionUtils;
 
@@ -56,22 +57,23 @@ public class DictionaryWriter extends AbstractDictionaryWriter {
     // TODO: Create "cache dictionary" to cache fresh words for frequently updated dictionaries,
     // considering performance regression.
     @Override
-    public void addUnigramWord(final String word, final String shortcutTarget, final int frequency,
-            final int shortcutFreq, final boolean isNotAWord) {
+    public void addUnigramWord(final String word, final String shortcutTarget,
+            final int probability, final int shortcutProbability, final boolean isNotAWord) {
         if (shortcutTarget == null) {
-            mFusionDictionary.add(word, frequency, null, isNotAWord);
+            mFusionDictionary.add(word, new ProbabilityInfo(probability), null, isNotAWord);
         } else {
             // TODO: Do this in the subclass, with this class taking an arraylist.
             final ArrayList<WeightedString> shortcutTargets = CollectionUtils.newArrayList();
-            shortcutTargets.add(new WeightedString(shortcutTarget, shortcutFreq));
-            mFusionDictionary.add(word, frequency, shortcutTargets, isNotAWord);
+            shortcutTargets.add(new WeightedString(shortcutTarget, shortcutProbability));
+            mFusionDictionary.add(word, new ProbabilityInfo(probability), shortcutTargets,
+                    isNotAWord);
         }
     }
 
     @Override
-    public void addBigramWords(final String word0, final String word1, final int frequency,
+    public void addBigramWords(final String word0, final String word1, final int probability,
             final boolean isValid, final long lastModifiedTime) {
-        mFusionDictionary.setBigram(word0, word1, frequency);
+        mFusionDictionary.setBigram(word0, word1, new ProbabilityInfo(probability));
     }
 
     @Override
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
index 782ada3f4..247d81ad3 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictDecoderUtils.java
@@ -408,7 +408,7 @@ public final class BinaryDictDecoderUtils {
     private static WeightedString getWordAtPositionWithParentAddress(final DictDecoder dictDecoder,
             final int pos, final FormatOptions options) {
         int currentPos = pos;
-        int frequency = Integer.MIN_VALUE;
+        ProbabilityInfo probabilityInfo = null;
         final StringBuilder builder = new StringBuilder();
         // the length of the path from the root to the leaf is limited by MAX_WORD_LENGTH
         for (int count = 0; count < FormatSpec.MAX_WORD_LENGTH; ++count) {
@@ -424,13 +424,15 @@ public final class BinaryDictDecoderUtils {
                     MakedictLog.d("Too many jumps - probably a bug");
                 }
             } while (BinaryDictIOUtils.isMovedPtNode(currentInfo.mFlags, options));
-            if (Integer.MIN_VALUE == frequency) frequency = currentInfo.mFrequency;
+            if (probabilityInfo == null) {
+                probabilityInfo = currentInfo.mProbabilityInfo;
+            }
             builder.insert(0,
                     new String(currentInfo.mCharacters, 0, currentInfo.mCharacters.length));
             if (currentInfo.mParentAddress == FormatSpec.NO_PARENT_ADDRESS) break;
             currentPos = currentInfo.mParentAddress + currentInfo.mOriginalAddress;
         }
-        return new WeightedString(builder.toString(), frequency);
+        return new WeightedString(builder.toString(), probabilityInfo);
     }
 
     private static WeightedString getWordAtPositionWithoutParentAddress(
@@ -448,7 +450,7 @@ public final class BinaryDictDecoderUtils {
             groupPos = info.mEndAddress;
             if (info.mOriginalAddress == pos) {
                 builder.append(new String(info.mCharacters, 0, info.mCharacters.length));
-                result = new WeightedString(builder.toString(), info.mFrequency);
+                result = new WeightedString(builder.toString(), info.mProbabilityInfo);
                 break; // and return
             }
             if (BinaryDictIOUtils.hasChildrenAddress(info.mChildrenAddress)) {
@@ -527,13 +529,13 @@ public final class BinaryDictDecoderUtils {
                     }
                     nodeArrayContents.add(
                             new PtNode(info.mCharacters, shortcutTargets, bigrams,
-                                    info.mFrequency,
+                                    info.mProbabilityInfo,
                                     0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
                                     0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED), children));
                 } else {
                     nodeArrayContents.add(
                             new PtNode(info.mCharacters, shortcutTargets, bigrams,
-                                    info.mFrequency,
+                                    info.mProbabilityInfo,
                                     0 != (info.mFlags & FormatSpec.FLAG_IS_NOT_A_WORD),
                                     0 != (info.mFlags & FormatSpec.FLAG_IS_BLACKLISTED)));
                 }
@@ -611,7 +613,7 @@ public final class BinaryDictDecoderUtils {
                     newDict.addBlacklistEntry(wordProperty.mWord, wordProperty.mShortcutTargets,
                             wordProperty.mIsNotAWord);
                 } else {
-                    newDict.add(wordProperty.mWord, wordProperty.getProbability(),
+                    newDict.add(wordProperty.mWord, wordProperty.mProbabilityInfo,
                             wordProperty.mShortcutTargets, wordProperty.mIsNotAWord);
                 }
             }
@@ -620,7 +622,7 @@ public final class BinaryDictDecoderUtils {
                 // words that are not also registered as unigrams so we don't have to avoid
                 // them explicitly here.
                 for (final WeightedString bigram : wordProperty.mBigrams) {
-                    newDict.setBigram(wordProperty.mWord, bigram.mWord, bigram.getProbability());
+                    newDict.setBigram(wordProperty.mWord, bigram.mWord, bigram.mProbabilityInfo);
                 }
             }
         }
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
index eff8fc375..9c5d1b9d7 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictEncoderUtils.java
@@ -673,7 +673,7 @@ public class BinaryDictEncoderUtils {
 
     /* package */ static byte makePtNodeFlags(final PtNode node, final int childrenOffset,
             final FormatOptions formatOptions) {
-        return (byte) makePtNodeFlags(node.mChars.length > 1, node.mFrequency >= 0,
+        return (byte) makePtNodeFlags(node.mChars.length > 1, node.isTerminal(),
                 getByteSize(childrenOffset),
                 node.mShortcutTargets != null && !node.mShortcutTargets.isEmpty(),
                 node.mBigrams != null, node.mIsNotAWord, node.mIsBlacklistEntry, formatOptions);
@@ -833,10 +833,10 @@ public class BinaryDictEncoderUtils {
                         + ptNode.mCachedAddressAfterUpdate);
             }
             // Sanity checks.
-            if (DBG && ptNode.mFrequency > FormatSpec.MAX_TERMINAL_FREQUENCY) {
+            if (DBG && ptNode.getProbability() > FormatSpec.MAX_TERMINAL_FREQUENCY) {
                 throw new RuntimeException("A node has a frequency > "
                         + FormatSpec.MAX_TERMINAL_FREQUENCY
-                        + " : " + ptNode.mFrequency);
+                        + " : " + ptNode.mProbabilityInfo.toString());
             }
             dictEncoder.writePtNode(ptNode, parentPosition, formatOptions, dict);
         }
@@ -871,7 +871,7 @@ public class BinaryDictEncoderUtils {
             for (final PtNode ptNode : ptNodeArray.mData) {
                 ++ptNodes;
                 if (ptNode.mChars.length > maxRuns) maxRuns = ptNode.mChars.length;
-                if (ptNode.mFrequency >= 0) {
+                if (ptNode.isTerminal()) {
                     if (ptNodeArray.mCachedAddressAfterUpdate < firstTerminalAddress)
                         firstTerminalAddress = ptNodeArray.mCachedAddressAfterUpdate;
                     if (ptNodeArray.mCachedAddressAfterUpdate > lastTerminalAddress)
diff --git a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
index dea9f2e28..67f86d44e 100644
--- a/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
+++ b/java/src/com/android/inputmethod/latin/makedict/BinaryDictIOUtils.java
@@ -91,21 +91,23 @@ public final class BinaryDictIOUtils {
                 stack.pop();
                 continue;
             }
-            PtNodeInfo info = dictDecoder.readPtNode(p.mAddress, formatOptions);
-            for (int i = 0; i < info.mCharacters.length; ++i) {
-                pushedChars[index++] = info.mCharacters[i];
+            final PtNodeInfo ptNodeInfo = dictDecoder.readPtNode(p.mAddress, formatOptions);
+            for (int i = 0; i < ptNodeInfo.mCharacters.length; ++i) {
+                pushedChars[index++] = ptNodeInfo.mCharacters[i];
             }
             p.mPosition++;
 
-            final boolean isMovedPtNode = isMovedPtNode(info.mFlags,
+            final boolean isMovedPtNode = isMovedPtNode(ptNodeInfo.mFlags,
                     formatOptions);
-            final boolean isDeletedPtNode = isDeletedPtNode(info.mFlags,
+            final boolean isDeletedPtNode = isDeletedPtNode(ptNodeInfo.mFlags,
                     formatOptions);
-            if (!isMovedPtNode && !isDeletedPtNode
-                    && info.mFrequency != FusionDictionary.PtNode.NOT_A_TERMINAL) {// found word
-                words.put(info.mOriginalAddress, new String(pushedChars, 0, index));
-                frequencies.put(info.mOriginalAddress, info.mFrequency);
-                if (info.mBigrams != null) bigrams.put(info.mOriginalAddress, info.mBigrams);
+            if (!isMovedPtNode && !isDeletedPtNode && ptNodeInfo.isTerminal()) {// found word
+                words.put(ptNodeInfo.mOriginalAddress, new String(pushedChars, 0, index));
+                frequencies.put(
+                        ptNodeInfo.mOriginalAddress, ptNodeInfo.mProbabilityInfo.mProbability);
+                if (ptNodeInfo.mBigrams != null) {
+                    bigrams.put(ptNodeInfo.mOriginalAddress, ptNodeInfo.mBigrams);
+                }
             }
 
             if (p.mPosition == p.mNumOfPtNode) {
@@ -127,8 +129,8 @@ public final class BinaryDictIOUtils {
                 p.mAddress = dictDecoder.getPosition();
             }
 
-            if (!isMovedPtNode && hasChildrenAddress(info.mChildrenAddress)) {
-                final Position childrenPos = new Position(info.mChildrenAddress, index);
+            if (!isMovedPtNode && hasChildrenAddress(ptNodeInfo.mChildrenAddress)) {
+                final Position childrenPos = new Position(ptNodeInfo.mChildrenAddress, index);
                 stack.push(childrenPos);
             }
         }
@@ -203,8 +205,7 @@ public final class BinaryDictIOUtils {
                     if (same) {
                         // found the PtNode matches the word.
                         if (wordPos + currentInfo.mCharacters.length == wordLen) {
-                            if (currentInfo.mFrequency == PtNode.NOT_A_TERMINAL
-                                    || isDeletedNode) {
+                            if (!currentInfo.isTerminal() || isDeletedNode) {
                                 return FormatSpec.NOT_VALID_WORD;
                             } else {
                                 return ptNodePos;
diff --git a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
index ca4a2e9bb..8f73b27b5 100644
--- a/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
+++ b/java/src/com/android/inputmethod/latin/makedict/FusionDictionary.java
@@ -107,24 +107,26 @@ public final class FusionDictionary implements Iterable<WordProperty> {
     }
 
     /**
-     * PtNode is a group of characters, with a frequency, shortcut targets, bigrams, and children
-     * (Pt means Patricia Trie).
+     * PtNode is a group of characters, with probability information, shortcut targets, bigrams,
+     * and children (Pt means Patricia Trie).
      *
      * This is the central class of the in-memory representation. A PtNode is what can
      * be seen as a traditional "trie node", except it can hold several characters at the
      * same time. A PtNode essentially represents one or several characters in the middle
      * of the trie tree; as such, it can be a terminal, and it can have children.
      * In this in-memory representation, whether the PtNode is a terminal or not is represented
-     * in the frequency, where NOT_A_TERMINAL (= -1) means this is not a terminal and any other
-     * value is the frequency of this terminal. A terminal may have non-null shortcuts and/or
-     * bigrams, but a non-terminal may not. Moreover, children, if present, are null.
+     * by mProbabilityInfo. The PtNode is a terminal when the mProbabilityInfo is not null and the
+     * PtNode is not a terminal when the mProbabilityInfo is null. A terminal may have non-null
+     * shortcuts and/or bigrams, but a non-terminal may not. Moreover, children, if present,
+     * are non-null.
      */
     public static final class PtNode {
-        public static final int NOT_A_TERMINAL = -1;
+        private static final int NOT_A_TERMINAL = -1;
         final int mChars[];
         ArrayList<WeightedString> mShortcutTargets;
         ArrayList<WeightedString> mBigrams;
-        int mFrequency; // NOT_A_TERMINAL == mFrequency indicates this is not a terminal.
+        // null == mProbabilityInfo indicates this is not a terminal.
+        ProbabilityInfo mProbabilityInfo;
         int mTerminalId; // NOT_A_TERMINAL == mTerminalId indicates this is not a terminal.
         PtNodeArray mChildren;
         boolean mIsNotAWord; // Only a shortcut
@@ -140,11 +142,11 @@ public final class FusionDictionary implements Iterable<WordProperty> {
         int mCachedAddressAfterUpdate; // The address of this PtNode (after update)
 
         public PtNode(final int[] chars, final ArrayList<WeightedString> shortcutTargets,
-                final ArrayList<WeightedString> bigrams, final int frequency,
+                final ArrayList<WeightedString> bigrams, final ProbabilityInfo probabilityInfo,
                 final boolean isNotAWord, final boolean isBlacklistEntry) {
             mChars = chars;
-            mFrequency = frequency;
-            mTerminalId = frequency;
+            mProbabilityInfo = probabilityInfo;
+            mTerminalId = probabilityInfo == null ? NOT_A_TERMINAL : probabilityInfo.mProbability;
             mShortcutTargets = shortcutTargets;
             mBigrams = bigrams;
             mChildren = null;
@@ -153,11 +155,11 @@ public final class FusionDictionary implements Iterable<WordProperty> {
         }
 
         public PtNode(final int[] chars, final ArrayList<WeightedString> shortcutTargets,
-                final ArrayList<WeightedString> bigrams, final int frequency,
+                final ArrayList<WeightedString> bigrams, final ProbabilityInfo probabilityInfo,
                 final boolean isNotAWord, final boolean isBlacklistEntry,
                 final PtNodeArray children) {
             mChars = chars;
-            mFrequency = frequency;
+            mProbabilityInfo = probabilityInfo;
             mShortcutTargets = shortcutTargets;
             mBigrams = bigrams;
             mChildren = children;
@@ -177,11 +179,15 @@ public final class FusionDictionary implements Iterable<WordProperty> {
         }
 
         public boolean isTerminal() {
-            return NOT_A_TERMINAL != mFrequency;
+            return mProbabilityInfo != null;
         }
 
-        public int getFrequency() {
-            return mFrequency;
+        public int getProbability() {
+            if (isTerminal()) {
+                return mProbabilityInfo.mProbability;
+            } else {
+                return NOT_A_TERMINAL;
+            }
         }
 
         public boolean getIsNotAWord() {
@@ -213,18 +219,18 @@ public final class FusionDictionary implements Iterable<WordProperty> {
         }
 
         /**
-         * Adds a word to the bigram list. Updates the probability if the word already
+         * Adds a word to the bigram list. Updates the probability information if the word already
          * exists.
          */
-        public void addBigram(final String word, final int probability) {
+        public void addBigram(final String word, final ProbabilityInfo probabilityInfo) {
             if (mBigrams == null) {
                 mBigrams = new ArrayList<WeightedString>();
             }
             WeightedString bigram = getBigram(word);
             if (bigram != null) {
-                bigram.setProbability(probability);
+                bigram.mProbabilityInfo = probabilityInfo;
             } else {
-                bigram = new WeightedString(word, probability);
+                bigram = new WeightedString(word, probabilityInfo);
                 mBigrams.add(bigram);
             }
         }
@@ -270,12 +276,11 @@ public final class FusionDictionary implements Iterable<WordProperty> {
          * the existing ones if any. Note: unigram, bigram, and shortcut frequencies are only
          * updated if they are higher than the existing ones.
          */
-        public void update(final int frequency, final ArrayList<WeightedString> shortcutTargets,
+        private void update(final ProbabilityInfo probabilityInfo,
+                final ArrayList<WeightedString> shortcutTargets,
                 final ArrayList<WeightedString> bigrams,
                 final boolean isNotAWord, final boolean isBlacklistEntry) {
-            if (frequency > mFrequency) {
-                mFrequency = frequency;
-            }
+            mProbabilityInfo = ProbabilityInfo.max(mProbabilityInfo, probabilityInfo);
             if (shortcutTargets != null) {
                 if (mShortcutTargets == null) {
                     mShortcutTargets = shortcutTargets;
@@ -286,8 +291,9 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                         final WeightedString existingShortcut = getShortcut(shortcut.mWord);
                         if (existingShortcut == null) {
                             mShortcutTargets.add(shortcut);
-                        } else if (existingShortcut.getProbability() < shortcut.getProbability()) {
-                            existingShortcut.setProbability(shortcut.getProbability());
+                        } else {
+                            existingShortcut.mProbabilityInfo = ProbabilityInfo.max(
+                                    existingShortcut.mProbabilityInfo, shortcut.mProbabilityInfo);
                         }
                     }
                 }
@@ -302,8 +308,9 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                         final WeightedString existingBigram = getBigram(bigram.mWord);
                         if (existingBigram == null) {
                             mBigrams.add(bigram);
-                        } else if (existingBigram.getProbability() < bigram.getProbability()) {
-                            existingBigram.setProbability(bigram.getProbability());
+                        } else {
+                            existingBigram.mProbabilityInfo = ProbabilityInfo.max(
+                                    existingBigram.mProbabilityInfo, bigram.mProbabilityInfo);
                         }
                     }
                 }
@@ -393,13 +400,13 @@ public final class FusionDictionary implements Iterable<WordProperty> {
      * they will be added to the dictionary as necessary.
      *
      * @param word the word to add.
-     * @param frequency the frequency of the word, in the range [0..255].
+     * @param probabilityInfo probability information of the word.
      * @param shortcutTargets a list of shortcut targets for this word, or null.
      * @param isNotAWord true if this should not be considered a word (e.g. shortcut only)
      */
-    public void add(final String word, final int frequency,
+    public void add(final String word, final ProbabilityInfo probabilityInfo,
             final ArrayList<WeightedString> shortcutTargets, final boolean isNotAWord) {
-        add(getCodePoints(word), frequency, shortcutTargets, isNotAWord,
+        add(getCodePoints(word), probabilityInfo, shortcutTargets, isNotAWord,
                 false /* isBlacklistEntry */);
     }
 
@@ -412,7 +419,8 @@ public final class FusionDictionary implements Iterable<WordProperty> {
      */
     public void addBlacklistEntry(final String word,
             final ArrayList<WeightedString> shortcutTargets, final boolean isNotAWord) {
-        add(getCodePoints(word), 0, shortcutTargets, isNotAWord, true /* isBlacklistEntry */);
+        add(getCodePoints(word), new ProbabilityInfo(0), shortcutTargets, isNotAWord,
+                true /* isBlacklistEntry */);
     }
 
     /**
@@ -438,21 +446,22 @@ public final class FusionDictionary implements Iterable<WordProperty> {
      *
      * @param word0 the previous word of the context
      * @param word1 the next word of the context
-     * @param frequency the bigram frequency
+     * @param probabilityInfo the bigram probability info
      */
-    public void setBigram(final String word0, final String word1, final int frequency) {
+    public void setBigram(final String word0, final String word1,
+            final ProbabilityInfo probabilityInfo) {
         PtNode ptNode0 = findWordInTree(mRootNodeArray, word0);
         if (ptNode0 != null) {
             final PtNode ptNode1 = findWordInTree(mRootNodeArray, word1);
             if (ptNode1 == null) {
-                add(getCodePoints(word1), 0, null, false /* isNotAWord */,
+                add(getCodePoints(word1), new ProbabilityInfo(0), null, false /* isNotAWord */,
                         false /* isBlacklistEntry */);
                 // The PtNode for the first word may have moved by the above insertion,
                 // if word1 and word2 share a common stem that happens not to have been
                 // a cutting point until now. In this case, we need to refresh ptNode.
                 ptNode0 = findWordInTree(mRootNodeArray, word0);
             }
-            ptNode0.addBigram(word1, frequency);
+            ptNode0.addBigram(word1, probabilityInfo);
         } else {
             throw new RuntimeException("First word of bigram not found " + word0);
         }
@@ -465,15 +474,15 @@ public final class FusionDictionary implements Iterable<WordProperty> {
      * an exception is thrown.
      *
      * @param word the word, as an int array.
-     * @param frequency the frequency of the word, in the range [0..255].
+     * @param probabilityInfo the probability information of the word.
      * @param shortcutTargets an optional list of shortcut targets for this word (null if none).
      * @param isNotAWord true if this is not a word for spellcheking purposes (shortcut only or so)
      * @param isBlacklistEntry true if this is a blacklisted word, false otherwise
      */
-    private void add(final int[] word, final int frequency,
+    private void add(final int[] word, final ProbabilityInfo probabilityInfo,
             final ArrayList<WeightedString> shortcutTargets,
             final boolean isNotAWord, final boolean isBlacklistEntry) {
-        assert(frequency >= 0 && frequency <= 255);
+        assert(probabilityInfo.mProbability <= FormatSpec.MAX_TERMINAL_FREQUENCY);
         if (word.length >= Constants.DICTIONARY_MAX_WORD_LENGTH) {
             MakedictLog.w("Ignoring a word that is too long: word.length = " + word.length);
             return;
@@ -501,7 +510,8 @@ public final class FusionDictionary implements Iterable<WordProperty> {
             // No node at this point to accept the word. Create one.
             final int insertionIndex = findInsertionIndex(currentNodeArray, word[charIndex]);
             final PtNode newPtNode = new PtNode(Arrays.copyOfRange(word, charIndex, word.length),
-                    shortcutTargets, null /* bigrams */, frequency, isNotAWord, isBlacklistEntry);
+                    shortcutTargets, null /* bigrams */, probabilityInfo, isNotAWord,
+                    isBlacklistEntry);
             currentNodeArray.mData.add(insertionIndex, newPtNode);
             if (DBG) checkStack(currentNodeArray);
         } else {
@@ -511,15 +521,15 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                     // The new word is a prefix of an existing word, but the node on which it
                     // should end already exists as is. Since the old PtNode was not a terminal,
                     // make it one by filling in its frequency and other attributes
-                    currentPtNode.update(frequency, shortcutTargets, null, isNotAWord,
+                    currentPtNode.update(probabilityInfo, shortcutTargets, null, isNotAWord,
                             isBlacklistEntry);
                 } else {
                     // The new word matches the full old word and extends past it.
                     // We only have to create a new node and add it to the end of this.
                     final PtNode newNode = new PtNode(
                             Arrays.copyOfRange(word, charIndex + differentCharIndex, word.length),
-                                    shortcutTargets, null /* bigrams */, frequency, isNotAWord,
-                                    isBlacklistEntry);
+                                    shortcutTargets, null /* bigrams */, probabilityInfo,
+                                    isNotAWord, isBlacklistEntry);
                     currentPtNode.mChildren = new PtNodeArray();
                     currentPtNode.mChildren.mData.add(newNode);
                 }
@@ -527,7 +537,7 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                 if (0 == differentCharIndex) {
                     // Exact same word. Update the frequency if higher. This will also add the
                     // new shortcuts to the existing shortcut list if it already exists.
-                    currentPtNode.update(frequency, shortcutTargets, null,
+                    currentPtNode.update(probabilityInfo, shortcutTargets, null,
                             currentPtNode.mIsNotAWord && isNotAWord,
                             currentPtNode.mIsBlacklistEntry || isBlacklistEntry);
                 } else {
@@ -537,7 +547,7 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                     final PtNode newOldWord = new PtNode(
                             Arrays.copyOfRange(currentPtNode.mChars, differentCharIndex,
                                     currentPtNode.mChars.length), currentPtNode.mShortcutTargets,
-                            currentPtNode.mBigrams, currentPtNode.mFrequency,
+                            currentPtNode.mBigrams, currentPtNode.mProbabilityInfo,
                             currentPtNode.mIsNotAWord, currentPtNode.mIsBlacklistEntry,
                             currentPtNode.mChildren);
                     newChildren.mData.add(newOldWord);
@@ -546,16 +556,17 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                     if (charIndex + differentCharIndex >= word.length) {
                         newParent = new PtNode(
                                 Arrays.copyOfRange(currentPtNode.mChars, 0, differentCharIndex),
-                                shortcutTargets, null /* bigrams */, frequency,
+                                shortcutTargets, null /* bigrams */, probabilityInfo,
                                 isNotAWord, isBlacklistEntry, newChildren);
                     } else {
                         newParent = new PtNode(
                                 Arrays.copyOfRange(currentPtNode.mChars, 0, differentCharIndex),
-                                null /* shortcutTargets */, null /* bigrams */, -1,
-                                false /* isNotAWord */, false /* isBlacklistEntry */, newChildren);
+                                null /* shortcutTargets */, null /* bigrams */,
+                                null /* probabilityInfo */, false /* isNotAWord */,
+                                false /* isBlacklistEntry */, newChildren);
                         final PtNode newWord = new PtNode(Arrays.copyOfRange(word,
                                 charIndex + differentCharIndex, word.length),
-                                shortcutTargets, null /* bigrams */, frequency,
+                                shortcutTargets, null /* bigrams */, probabilityInfo,
                                 isNotAWord, isBlacklistEntry);
                         final int addIndex = word[charIndex + differentCharIndex]
                                 > currentPtNode.mChars[differentCharIndex] ? 1 : 0;
@@ -617,8 +628,8 @@ public final class FusionDictionary implements Iterable<WordProperty> {
     private static int findInsertionIndex(final PtNodeArray nodeArray, int character) {
         final ArrayList<PtNode> data = nodeArray.mData;
         final PtNode reference = new PtNode(new int[] { character },
-                null /* shortcutTargets */, null /* bigrams */, 0, false /* isNotAWord */,
-                false /* isBlacklistEntry */);
+                null /* shortcutTargets */, null /* bigrams */, null /* probabilityInfo */,
+                false /* isNotAWord */, false /* isBlacklistEntry */);
         int result = Collections.binarySearch(data, reference, PTNODE_COMPARATOR);
         return result >= 0 ? result : -result - 1;
     }
@@ -752,8 +763,9 @@ public final class FusionDictionary implements Iterable<WordProperty> {
                         currentPos.length = mCurrentString.length();
                         mPositions.addLast(currentPos);
                     }
-                    if (currentPtNode.mFrequency >= 0) {
-                        return new WordProperty(mCurrentString.toString(), currentPtNode.mFrequency,
+                    if (currentPtNode.isTerminal()) {
+                        return new WordProperty(mCurrentString.toString(),
+                                currentPtNode.mProbabilityInfo,
                                 currentPtNode.mShortcutTargets, currentPtNode.mBigrams,
                                 currentPtNode.mIsNotAWord, currentPtNode.mIsBlacklistEntry);
                     }
diff --git a/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java b/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
index dafbc04b9..9dcd63f0c 100644
--- a/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
+++ b/java/src/com/android/inputmethod/latin/makedict/ProbabilityInfo.java
@@ -30,6 +30,21 @@ public final class ProbabilityInfo {
     public final int mLevel;
     public final int mCount;
 
+    public static ProbabilityInfo max(final ProbabilityInfo probabilityInfo1,
+            final ProbabilityInfo probabilityInfo2) {
+        if (probabilityInfo1 == null) {
+            return probabilityInfo2;
+        }
+        if (probabilityInfo2 == null) {
+            return probabilityInfo1;
+        }
+        if (probabilityInfo1.mProbability > probabilityInfo2.mProbability) {
+            return probabilityInfo1;
+        } else {
+            return probabilityInfo2;
+        }
+    }
+
     public ProbabilityInfo(final int probability) {
         this(probability, BinaryDictionary.NOT_A_VALID_TIMESTAMP, 0, 0);
     }
diff --git a/java/src/com/android/inputmethod/latin/makedict/PtNodeInfo.java b/java/src/com/android/inputmethod/latin/makedict/PtNodeInfo.java
index 188de7a0f..4760aa8d5 100644
--- a/java/src/com/android/inputmethod/latin/makedict/PtNodeInfo.java
+++ b/java/src/com/android/inputmethod/latin/makedict/PtNodeInfo.java
@@ -29,24 +29,28 @@ public final class PtNodeInfo {
     public final int mEndAddress;
     public final int mFlags;
     public final int[] mCharacters;
-    public final int mFrequency;
+    public final ProbabilityInfo mProbabilityInfo;
     public final int mChildrenAddress;
     public final int mParentAddress;
     public final ArrayList<WeightedString> mShortcutTargets;
     public final ArrayList<PendingAttribute> mBigrams;
 
     public PtNodeInfo(final int originalAddress, final int endAddress, final int flags,
-            final int[] characters, final int frequency, final int parentAddress,
+            final int[] characters, final ProbabilityInfo probabilityInfo, final int parentAddress,
             final int childrenAddress, final ArrayList<WeightedString> shortcutTargets,
             final ArrayList<PendingAttribute> bigrams) {
         mOriginalAddress = originalAddress;
         mEndAddress = endAddress;
         mFlags = flags;
         mCharacters = characters;
-        mFrequency = frequency;
+        mProbabilityInfo = probabilityInfo;
         mParentAddress = parentAddress;
         mChildrenAddress = childrenAddress;
         mShortcutTargets = shortcutTargets;
         mBigrams = bigrams;
     }
+
+    public boolean isTerminal() {
+        return mProbabilityInfo != null;
+    }
 }
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver2DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver2DictDecoder.java
index d35f780cf..f22b118d9 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver2DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver2DictDecoder.java
@@ -39,8 +39,9 @@ public class Ver2DictDecoder extends AbstractDictDecoder {
     private static final String TAG = Ver2DictDecoder.class.getSimpleName();
 
     protected static class PtNodeReader extends AbstractDictDecoder.PtNodeReader {
-        private static int readFrequency(final DictBuffer dictBuffer) {
-            return dictBuffer.readUnsignedByte();
+        private static ProbabilityInfo readProbabilityInfo(final DictBuffer dictBuffer) {
+            // Ver2 dicts don't contain historical information.
+            return new ProbabilityInfo(dictBuffer.readUnsignedByte());
         }
     }
 
@@ -133,12 +134,12 @@ public class Ver2DictDecoder extends AbstractDictDecoder {
             addressPointer += CharEncoding.getCharSize(character);
             characters = new int[] { character };
         }
-        final int frequency;
+        final ProbabilityInfo probabilityInfo;
         if (0 != (FormatSpec.FLAG_IS_TERMINAL & flags)) {
-            frequency = PtNodeReader.readFrequency(mDictBuffer);
+            probabilityInfo = PtNodeReader.readProbabilityInfo(mDictBuffer);
             addressPointer += FormatSpec.PTNODE_FREQUENCY_SIZE;
         } else {
-            frequency = PtNode.NOT_A_TERMINAL;
+            probabilityInfo = null;
         }
         int childrenAddress = PtNodeReader.readChildrenAddress(mDictBuffer, flags, options);
         if (childrenAddress != FormatSpec.NO_CHILDREN_ADDRESS) {
@@ -166,7 +167,7 @@ public class Ver2DictDecoder extends AbstractDictDecoder {
         } else {
             bigrams = null;
         }
-        return new PtNodeInfo(ptNodePos, addressPointer, flags, characters, frequency,
+        return new PtNodeInfo(ptNodePos, addressPointer, flags, characters, probabilityInfo,
                 parentAddress, childrenAddress, shortcutTargets, bigrams);
     }
 
@@ -231,7 +232,9 @@ public class Ver2DictDecoder extends AbstractDictDecoder {
         BinaryDictIOUtils.skipString(mDictBuffer,
                 (flags & FormatSpec.FLAG_HAS_MULTIPLE_CHARS) != 0);
         PtNodeReader.readChildrenAddress(mDictBuffer, flags, formatOptions);
-        if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) PtNodeReader.readFrequency(mDictBuffer);
+        if ((flags & FormatSpec.FLAG_IS_TERMINAL) != 0) {
+            PtNodeReader.readProbabilityInfo(mDictBuffer);
+        }
         if ((flags & FormatSpec.FLAG_HAS_SHORTCUT_TARGETS) != 0) {
             final int shortcutsSize = mDictBuffer.readUnsignedShort();
             mDictBuffer.position(mDictBuffer.position() + shortcutsSize
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
index 3de083ef3..634f63137 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver2DictEncoder.java
@@ -227,7 +227,7 @@ public class Ver2DictEncoder implements DictEncoder {
             final PtNode target =
                     FusionDictionary.findWordInTree(dict.mRootNodeArray, bigram.mWord);
             final int addressOfBigram = target.mCachedAddressAfterUpdate;
-            final int unigramFrequencyForThisWord = target.mFrequency;
+            final int unigramFrequencyForThisWord = target.getProbability();
             final int offset = addressOfBigram
                     - (mPosition + FormatSpec.PTNODE_ATTRIBUTE_FLAGS_SIZE);
             final int bigramFlags = BinaryDictEncoderUtils.makeBigramFlags(bigramIterator.hasNext(),
@@ -251,7 +251,7 @@ public class Ver2DictEncoder implements DictEncoder {
         writePtNodeFlags(ptNode, formatOptions);
         writeParentPosition(parentPosition, ptNode, formatOptions);
         writeCharacters(ptNode.mChars, ptNode.hasSeveralChars());
-        writeFrequency(ptNode.mFrequency);
+        writeFrequency(ptNode.getProbability());
         writeChildrenPosition(ptNode, formatOptions);
         writeShortcuts(ptNode.mShortcutTargets);
         writeBigrams(ptNode.mBigrams, dict);
diff --git a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
index 83707480d..1c74852fe 100644
--- a/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
+++ b/java/src/com/android/inputmethod/latin/makedict/Ver4DictDecoder.java
@@ -81,14 +81,11 @@ public class Ver4DictDecoder extends AbstractDictDecoder {
 
         // Insert unigrams to the fusion dictionary.
         for (final WordProperty wordProperty : wordProperties) {
-            // TODO: Support probability that is -1.
-            final int probability = wordProperty.getProbability() < 0 ?
-                    0 : wordProperty.getProbability();
             if (wordProperty.mIsBlacklistEntry) {
                 fusionDict.addBlacklistEntry(wordProperty.mWord, wordProperty.mShortcutTargets,
                         wordProperty.mIsNotAWord);
             } else {
-                fusionDict.add(wordProperty.mWord, probability,
+                fusionDict.add(wordProperty.mWord, wordProperty.mProbabilityInfo,
                         wordProperty.mShortcutTargets, wordProperty.mIsNotAWord);
             }
         }
@@ -99,7 +96,7 @@ public class Ver4DictDecoder extends AbstractDictDecoder {
             }
             final String word0 = wordProperty.mWord;
             for (final WeightedString bigram : wordProperty.mBigrams) {
-                fusionDict.setBigram(word0, bigram.mWord, bigram.getProbability());
+                fusionDict.setBigram(word0, bigram.mWord, bigram.mProbabilityInfo);
             }
         }
         return fusionDict;
diff --git a/java/src/com/android/inputmethod/latin/makedict/WordProperty.java b/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
index b93a0a525..1fc61e10a 100644
--- a/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
+++ b/java/src/com/android/inputmethod/latin/makedict/WordProperty.java
@@ -43,12 +43,12 @@ public final class WordProperty implements Comparable<WordProperty> {
 
     private int mHashCode = 0;
 
-    public WordProperty(final String word, final int probability,
+    public WordProperty(final String word, final ProbabilityInfo probabilityInfo,
             final ArrayList<WeightedString> shortcutTargets,
             final ArrayList<WeightedString> bigrams,
             final boolean isNotAWord, final boolean isBlacklistEntry) {
         mWord = word;
-        mProbabilityInfo = new ProbabilityInfo(probability);
+        mProbabilityInfo = probabilityInfo;
         mShortcutTargets = shortcutTargets;
         mBigrams = bigrams;
         mIsNotAWord = isNotAWord;