native/src/unigram_dictionary.cpp

/*
**
** Copyright 2010, 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.
*/

#include <assert.h>
#include <string.h>

#define LOG_TAG "LatinIME: unigram_dictionary.cpp"

#include "char_utils.h"
#include "dictionary.h"
#include "unigram_dictionary.h"

#include "binary_format.h"

namespace latinime {

const UnigramDictionary::digraph_t UnigramDictionary::GERMAN_UMLAUT_DIGRAPHS[] =
        { { 'a', 'e' },
        { 'o', 'e' },
        { 'u', 'e' } };

// TODO: check the header
UnigramDictionary::UnigramDictionary(const uint8_t* const streamStart, int typedLetterMultiplier,
        int fullWordMultiplier, int maxWordLength, int maxWords, int maxProximityChars,
        const bool isLatestDictVersion)
    : DICT_ROOT(streamStart + NEW_DICTIONARY_HEADER_SIZE),
    MAX_WORD_LENGTH(maxWordLength), MAX_WORDS(maxWords),
    MAX_PROXIMITY_CHARS(maxProximityChars), IS_LATEST_DICT_VERSION(isLatestDictVersion),
    TYPED_LETTER_MULTIPLIER(typedLetterMultiplier), FULL_WORD_MULTIPLIER(fullWordMultiplier),
      // TODO : remove this variable.
    ROOT_POS(0),
    BYTES_IN_ONE_CHAR(MAX_PROXIMITY_CHARS * sizeof(int)),
    MAX_UMLAUT_SEARCH_DEPTH(DEFAULT_MAX_UMLAUT_SEARCH_DEPTH) {
    if (DEBUG_DICT) {
        LOGI("UnigramDictionary - constructor");
    }
    mCorrection = new Correction(typedLetterMultiplier, fullWordMultiplier);
}

UnigramDictionary::~UnigramDictionary() {
    delete mCorrection;
}

static inline unsigned int getCodesBufferSize(const int* codes, const int codesSize,
        const int MAX_PROXIMITY_CHARS) {
    return sizeof(*codes) * MAX_PROXIMITY_CHARS * codesSize;
}

bool UnigramDictionary::isDigraph(const int* codes, const int i, const int codesSize) const {

    // There can't be a digraph if we don't have at least 2 characters to examine
    if (i + 2 > codesSize) return false;

    // Search for the first char of some digraph
    int lastDigraphIndex = -1;
    const int thisChar = codes[i * MAX_PROXIMITY_CHARS];
    for (lastDigraphIndex = sizeof(GERMAN_UMLAUT_DIGRAPHS) / sizeof(GERMAN_UMLAUT_DIGRAPHS[0]) - 1;
            lastDigraphIndex >= 0; --lastDigraphIndex) {
        if (thisChar == GERMAN_UMLAUT_DIGRAPHS[lastDigraphIndex].first) break;
    }
    // No match: return early
    if (lastDigraphIndex < 0) return false;

    // It's an interesting digraph if the second char matches too.
    return GERMAN_UMLAUT_DIGRAPHS[lastDigraphIndex].second == codes[(i + 1) * MAX_PROXIMITY_CHARS];
}

// Mostly the same arguments as the non-recursive version, except:
// codes is the original value. It points to the start of the work buffer, and gets passed as is.
// codesSize is the size of the user input (thus, it is the size of codesSrc).
// codesDest is the current point in the work buffer.
// codesSrc is the current point in the user-input, original, content-unmodified buffer.
// codesRemain is the remaining size in codesSrc.
void UnigramDictionary::getWordWithDigraphSuggestionsRec(ProximityInfo *proximityInfo,
        const int *xcoordinates, const int* ycoordinates, const int *codesBuffer,
        const int codesBufferSize, const int flags, const int* codesSrc, const int codesRemain,
        const int currentDepth, int* codesDest, unsigned short* outWords, int* frequencies) {

    if (currentDepth < MAX_UMLAUT_SEARCH_DEPTH) {
        for (int i = 0; i < codesRemain; ++i) {
            if (isDigraph(codesSrc, i, codesRemain)) {
                // Found a digraph. We will try both spellings. eg. the word is "pruefen"

                // Copy the word up to the first char of the digraph, then continue processing
                // on the remaining part of the word, skipping the second char of the digraph.
                // In our example, copy "pru" and continue running on "fen"
                // Make i the index of the second char of the digraph for simplicity. Forgetting
                // to do that results in an infinite recursion so take care!
                ++i;
                memcpy(codesDest, codesSrc, i * BYTES_IN_ONE_CHAR);
                getWordWithDigraphSuggestionsRec(proximityInfo, xcoordinates, ycoordinates,
                        codesBuffer, codesBufferSize, flags,
                        codesSrc + (i + 1) * MAX_PROXIMITY_CHARS, codesRemain - i - 1,
                        currentDepth + 1, codesDest + i * MAX_PROXIMITY_CHARS, outWords,
                        frequencies);

                // Copy the second char of the digraph in place, then continue processing on
                // the remaining part of the word.
                // In our example, after "pru" in the buffer copy the "e", and continue on "fen"
                memcpy(codesDest + i * MAX_PROXIMITY_CHARS, codesSrc + i * MAX_PROXIMITY_CHARS,
                        BYTES_IN_ONE_CHAR);
                getWordWithDigraphSuggestionsRec(proximityInfo, xcoordinates, ycoordinates,
                        codesBuffer, codesBufferSize, flags, codesSrc + i * MAX_PROXIMITY_CHARS,
                        codesRemain - i, currentDepth + 1, codesDest + i * MAX_PROXIMITY_CHARS,
                        outWords, frequencies);
                return;
            }
        }
    }

    // If we come here, we hit the end of the word: let's check it against the dictionary.
    // In our example, we'll come here once for "prufen" and then once for "pruefen".
    // If the word contains several digraphs, we'll come it for the product of them.
    // eg. if the word is "ueberpruefen" we'll test, in order, against
    // "uberprufen", "uberpruefen", "ueberprufen", "ueberpruefen".
    const unsigned int remainingBytes = BYTES_IN_ONE_CHAR * codesRemain;
    if (0 != remainingBytes)
        memcpy(codesDest, codesSrc, remainingBytes);

    getWordSuggestions(proximityInfo, xcoordinates, ycoordinates, codesBuffer,
            (codesDest - codesBuffer) / MAX_PROXIMITY_CHARS + codesRemain, outWords, frequencies);
}

int UnigramDictionary::getSuggestions(ProximityInfo *proximityInfo, const int *xcoordinates,
        const int *ycoordinates, const int *codes, const int codesSize, const int flags,
        unsigned short *outWords, int *frequencies) {

    if (REQUIRES_GERMAN_UMLAUT_PROCESSING & flags)
    { // Incrementally tune the word and try all possibilities
        int codesBuffer[getCodesBufferSize(codes, codesSize, MAX_PROXIMITY_CHARS)];
        getWordWithDigraphSuggestionsRec(proximityInfo, xcoordinates, ycoordinates, codesBuffer,
                codesSize, flags, codes, codesSize, 0, codesBuffer, outWords, frequencies);
    } else { // Normal processing
        getWordSuggestions(proximityInfo, xcoordinates, ycoordinates, codes, codesSize,
                outWords, frequencies);
    }

    PROF_START(20);
    // Get the word count
    int suggestedWordsCount = 0;
    while (suggestedWordsCount < MAX_WORDS && mFrequencies[suggestedWordsCount] > 0) {
        suggestedWordsCount++;
    }

    if (DEBUG_DICT) {
        LOGI("Returning %d words", suggestedWordsCount);
        /// Print the returned words
        for (int j = 0; j < suggestedWordsCount; ++j) {
#ifdef FLAG_DBG
            short unsigned int* w = mOutputChars + j * MAX_WORD_LENGTH;
            char s[MAX_WORD_LENGTH];
            for (int i = 0; i <= MAX_WORD_LENGTH; i++) s[i] = w[i];
            LOGI("%s %i", s, mFrequencies[j]);
#endif
        }
    }
    PROF_END(20);
    PROF_CLOSE;
    return suggestedWordsCount;
}

void UnigramDictionary::getWordSuggestions(ProximityInfo *proximityInfo,
        const int *xcoordinates, const int *ycoordinates, const int *codes, const int codesSize,
        unsigned short *outWords, int *frequencies) {

    PROF_OPEN;
    PROF_START(0);
    initSuggestions(
            proximityInfo, xcoordinates, ycoordinates, codes, codesSize, outWords, frequencies);
    if (DEBUG_DICT) assert(codesSize == mInputLength);

    const int maxDepth = min(mInputLength * MAX_DEPTH_MULTIPLIER, MAX_WORD_LENGTH);
    mCorrection->initCorrection(mProximityInfo, mInputLength, maxDepth);
    PROF_END(0);

    // TODO: remove
    PROF_START(1);
    // Note: This line is intentionally left blank
    PROF_END(1);

    PROF_START(2);
    // Suggestion with missing character
    if (DEBUG_DICT) {
        LOGI("--- Suggest missing characters");
    }
    getSuggestionCandidates(0, -1, -1);
    PROF_END(2);

    PROF_START(3);
    // Suggestion with excessive character
    if (DEBUG_DICT) {
        LOGI("--- Suggest excessive characters");
    }
    getSuggestionCandidates(-1, 0, -1);
    PROF_END(3);

    PROF_START(4);
    // Suggestion with transposed characters
    // Only suggest words that length is mInputLength
    if (DEBUG_DICT) {
        LOGI("--- Suggest transposed characters");
    }
    getSuggestionCandidates(-1, -1, 0);
    PROF_END(4);

    PROF_START(5);
    // Suggestions with missing space
    if (SUGGEST_WORDS_WITH_MISSING_SPACE_CHARACTER
            && mInputLength >= MIN_USER_TYPED_LENGTH_FOR_MISSING_SPACE_SUGGESTION) {
        for (int i = 1; i < codesSize; ++i) {
            if (DEBUG_DICT) {
                LOGI("--- Suggest missing space characters %d", i);
            }
            getMissingSpaceWords(mInputLength, i, mCorrection);
        }
    }
    PROF_END(5);

    PROF_START(6);
    if (SUGGEST_WORDS_WITH_SPACE_PROXIMITY && proximityInfo) {
        // The first and last "mistyped spaces" are taken care of by excessive character handling
        for (int i = 1; i < codesSize - 1; ++i) {
            if (DEBUG_DICT) {
                LOGI("--- Suggest words with proximity space %d", i);
            }
            const int x = xcoordinates[i];
            const int y = ycoordinates[i];
            if (DEBUG_PROXIMITY_INFO) {
                LOGI("Input[%d] x = %d, y = %d, has space proximity = %d",
                        i, x, y, proximityInfo->hasSpaceProximity(x, y));
            }
            if (proximityInfo->hasSpaceProximity(x, y)) {
                getMistypedSpaceWords(mInputLength, i, mCorrection);
            }
        }
    }
    PROF_END(6);
}

void UnigramDictionary::initSuggestions(ProximityInfo *proximityInfo, const int *xcoordinates,
        const int *ycoordinates, const int *codes, const int codesSize,
        unsigned short *outWords, int *frequencies) {
    if (DEBUG_DICT) {
        LOGI("initSuggest");
    }
    mFrequencies = frequencies;
    mOutputChars = outWords;
    mInputLength = codesSize;
    proximityInfo->setInputParams(codes, codesSize);
    mProximityInfo = proximityInfo;
}

static inline void registerNextLetter(unsigned short c, int *nextLetters, int nextLettersSize) {
    if (c < nextLettersSize) {
        nextLetters[c]++;
    }
}

// TODO: We need to optimize addWord by using STL or something
// TODO: This needs to take an const unsigned short* and not tinker with its contents
bool UnigramDictionary::addWord(unsigned short *word, int length, int frequency) {
    word[length] = 0;
    if (DEBUG_DICT && DEBUG_SHOW_FOUND_WORD) {
#ifdef FLAG_DBG
        char s[length + 1];
        for (int i = 0; i <= length; i++) s[i] = word[i];
        LOGI("Found word = %s, freq = %d", s, frequency);
#endif
    }
    if (length > MAX_WORD_LENGTH) {
        if (DEBUG_DICT) {
            LOGI("Exceeded max word length.");
        }
        return false;
    }

    // Find the right insertion point
    int insertAt = 0;
    while (insertAt < MAX_WORDS) {
        // TODO: How should we sort words with the same frequency?
        if (frequency > mFrequencies[insertAt]) {
            break;
        }
        insertAt++;
    }
    if (insertAt < MAX_WORDS) {
        if (DEBUG_DICT) {
#ifdef FLAG_DBG
            char s[length + 1];
            for (int i = 0; i <= length; i++) s[i] = word[i];
            LOGI("Added word = %s, freq = %d, %d", s, frequency, S_INT_MAX);
#endif
        }
        memmove((char*) mFrequencies + (insertAt + 1) * sizeof(mFrequencies[0]),
               (char*) mFrequencies + insertAt * sizeof(mFrequencies[0]),
               (MAX_WORDS - insertAt - 1) * sizeof(mFrequencies[0]));
        mFrequencies[insertAt] = frequency;
        memmove((char*) mOutputChars + (insertAt + 1) * MAX_WORD_LENGTH * sizeof(short),
               (char*) mOutputChars + insertAt * MAX_WORD_LENGTH * sizeof(short),
               (MAX_WORDS - insertAt - 1) * sizeof(short) * MAX_WORD_LENGTH);
        unsigned short *dest = mOutputChars + insertAt * MAX_WORD_LENGTH;
        while (length--) {
            *dest++ = *word++;
        }
        *dest = 0; // NULL terminate
        if (DEBUG_DICT) {
            LOGI("Added word at %d", insertAt);
        }
        return true;
    }
    return false;
}

static const char QUOTE = '\'';
static const char SPACE = ' ';

void UnigramDictionary::getSuggestionCandidates(const int skipPos,
        const int excessivePos, const int transposedPos) {
    if (DEBUG_DICT) {
        assert(transposedPos + 1 < mInputLength);
        assert(excessivePos < mInputLength);
        assert(missingPos < mInputLength);
    }
    mCorrection->setCorrectionParams(skipPos, excessivePos, transposedPos,
            -1 /* spaceProximityPos */, -1 /* missingSpacePos */);
    int rootPosition = ROOT_POS;
    // Get the number of children of root, then increment the position
    int childCount = Dictionary::getCount(DICT_ROOT, &rootPosition);
    int outputIndex = 0;

    mCorrection->initCorrectionState(rootPosition, childCount, (mInputLength <= 0));

    // Depth first search
    while (outputIndex >= 0) {
        if (mCorrection->initProcessState(outputIndex)) {
            int siblingPos = mCorrection->getTreeSiblingPos(outputIndex);
            int firstChildPos;

            const bool needsToTraverseChildrenNodes = processCurrentNode(siblingPos,
                    mCorrection, &childCount, &firstChildPos, &siblingPos);
            // Update next sibling pos
            mCorrection->setTreeSiblingPos(outputIndex, siblingPos);

            if (needsToTraverseChildrenNodes) {
                // Goes to child node
                outputIndex = mCorrection->goDownTree(outputIndex, childCount, firstChildPos);
            }
        } else {
            // Goes to parent sibling node
            outputIndex = mCorrection->getTreeParentIndex(outputIndex);
        }
    }
}

static const int TWO_31ST_DIV_2 = S_INT_MAX / 2;
inline static void multiplyIntCapped(const int multiplier, int *base) {
    const int temp = *base;
    if (temp != S_INT_MAX) {
        // Branch if multiplier == 2 for the optimization
        if (multiplier == 2) {
            *base = TWO_31ST_DIV_2 >= temp ? temp << 1 : S_INT_MAX;
        } else {
            const int tempRetval = temp * multiplier;
            *base = tempRetval >= temp ? tempRetval : S_INT_MAX;
        }
    }
}

void UnigramDictionary::getMissingSpaceWords(
        const int inputLength, const int missingSpacePos, Correction *correction) {
    correction->setCorrectionParams(-1 /* skipPos */, -1 /* excessivePos */,
            -1 /* transposedPos */, -1 /* spaceProximityPos */, missingSpacePos);
    getSplitTwoWordsSuggestion(inputLength, correction);
}

void UnigramDictionary::getMistypedSpaceWords(
        const int inputLength, const int spaceProximityPos, Correction *correction) {
    correction->setCorrectionParams(-1 /* skipPos */, -1 /* excessivePos */,
            -1 /* transposedPos */, spaceProximityPos, -1 /* missingSpacePos */);
    getSplitTwoWordsSuggestion(inputLength, correction);
}

inline bool UnigramDictionary::needsToSkipCurrentNode(const unsigned short c,
        const int inputIndex, const int skipPos, const int depth) {
    const unsigned short userTypedChar = mProximityInfo->getPrimaryCharAt(inputIndex);
    // Skip the ' or other letter and continue deeper
    return (c == QUOTE && userTypedChar != QUOTE) || skipPos == depth;
}

inline void UnigramDictionary::onTerminal(const int freq, Correction *correction) {
    int wordLength;
    unsigned short* wordPointer;
    const int finalFreq = correction->getFinalFreq(freq, &wordPointer, &wordLength);
    if (finalFreq >= 0) {
        addWord(wordPointer, wordLength, finalFreq);
    }
}

void UnigramDictionary::getSplitTwoWordsSuggestion(
        const int inputLength, Correction* correction) {
    const int spaceProximityPos = correction->getSpaceProximityPos();
    const int missingSpacePos = correction->getMissingSpacePos();
    if (DEBUG_DICT) {
        int inputCount = 0;
        if (spaceProximityPos >= 0) ++inputCount;
        if (missingSpacePos >= 0) ++inputCount;
        assert(inputCount <= 1);
    }
    const bool isSpaceProximity = spaceProximityPos >= 0;
    const int firstWordStartPos = 0;
    const int secondWordStartPos = isSpaceProximity ? (spaceProximityPos + 1) : missingSpacePos;
    const int firstWordLength = isSpaceProximity ? spaceProximityPos : missingSpacePos;
    const int secondWordLength = isSpaceProximity
            ? (inputLength - spaceProximityPos - 1)
            : (inputLength - missingSpacePos);

    if (inputLength >= MAX_WORD_LENGTH) return;
    if (0 >= firstWordLength || 0 >= secondWordLength || firstWordStartPos >= secondWordStartPos
            || firstWordStartPos < 0 || secondWordStartPos + secondWordLength > inputLength)
        return;

    const int newWordLength = firstWordLength + secondWordLength + 1;
    // Allocating variable length array on stack
    unsigned short word[newWordLength];
    const int firstFreq = getMostFrequentWordLike(firstWordStartPos, firstWordLength, mWord);
    if (DEBUG_DICT) {
        LOGI("First freq: %d", firstFreq);
    }
    if (firstFreq <= 0) return;

    for (int i = 0; i < firstWordLength; ++i) {
        word[i] = mWord[i];
    }

    const int secondFreq = getMostFrequentWordLike(secondWordStartPos, secondWordLength, mWord);
    if (DEBUG_DICT) {
        LOGI("Second  freq:  %d", secondFreq);
    }
    if (secondFreq <= 0) return;

    word[firstWordLength] = SPACE;
    for (int i = (firstWordLength + 1); i < newWordLength; ++i) {
        word[i] = mWord[i - firstWordLength - 1];
    }

    const int pairFreq = mCorrection->getFreqForSplitTwoWords(firstFreq, secondFreq);
    if (DEBUG_DICT) {
        LOGI("Split two words:  %d, %d, %d, %d", firstFreq, secondFreq, pairFreq, inputLength);
    }
    addWord(word, newWordLength, pairFreq);
    return;
}

// Wrapper for getMostFrequentWordLikeInner, which matches it to the previous
// interface.
inline int UnigramDictionary::getMostFrequentWordLike(const int startInputIndex,
        const int inputLength, unsigned short *word) {
    uint16_t inWord[inputLength];

    for (int i = 0; i < inputLength; ++i) {
        inWord[i] = (uint16_t)mProximityInfo->getPrimaryCharAt(startInputIndex + i);
    }
    return getMostFrequentWordLikeInner(inWord, inputLength, word);
}

// This function will take the position of a character array within a CharGroup,
// and check it actually like-matches the word in inWord starting at startInputIndex,
// that is, it matches it with case and accents squashed.
// The function returns true if there was a full match, false otherwise.
// The function will copy on-the-fly the characters in the CharGroup to outNewWord.
// It will also place the end position of the array in outPos; in outInputIndex,
// it will place the index of the first char AFTER the match if there was a match,
// and the initial position if there was not. It makes sense because if there was
// a match we want to continue searching, but if there was not, we want to go to
// the next CharGroup.
// In and out parameters may point to the same location. This function takes care
// not to use any input parameters after it wrote into its outputs.
static inline bool testCharGroupForContinuedLikeness(const uint8_t flags,
        const uint8_t* const root, const int startPos,
        const uint16_t* const inWord, const int startInputIndex,
        int32_t* outNewWord, int* outInputIndex, int* outPos) {
    const bool hasMultipleChars = (0 != (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags));
    int pos = startPos;
    int32_t character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
    int32_t baseChar = Dictionary::toBaseLowerCase(character);
    const uint16_t wChar = Dictionary::toBaseLowerCase(inWord[startInputIndex]);

    if (baseChar != wChar) {
        *outPos = hasMultipleChars ? BinaryFormat::skipOtherCharacters(root, pos) : pos;
        *outInputIndex = startInputIndex;
        return false;
    }
    int inputIndex = startInputIndex;
    outNewWord[inputIndex] = character;
    if (hasMultipleChars) {
        character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
        while (NOT_A_CHARACTER != character) {
            baseChar = Dictionary::toBaseLowerCase(character);
            if (Dictionary::toBaseLowerCase(inWord[++inputIndex]) != baseChar) {
                *outPos = BinaryFormat::skipOtherCharacters(root, pos);
                *outInputIndex = startInputIndex;
                return false;
            }
            outNewWord[inputIndex] = character;
            character = BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
        }
    }
    *outInputIndex = inputIndex + 1;
    *outPos = pos;
    return true;
}

// This function is invoked when a word like the word searched for is found.
// It will compare the frequency to the max frequency, and if greater, will
// copy the word into the output buffer. In output value maxFreq, it will
// write the new maximum frequency if it changed.
static inline void onTerminalWordLike(const int freq, int32_t* newWord, const int length,
        short unsigned int* outWord, int* maxFreq) {
    if (freq > *maxFreq) {
        for (int q = 0; q < length; ++q)
            outWord[q] = newWord[q];
        outWord[length] = 0;
        *maxFreq = freq;
    }
}

// Will find the highest frequency of the words like the one passed as an argument,
// that is, everything that only differs by case/accents.
int UnigramDictionary::getMostFrequentWordLikeInner(const uint16_t * const inWord,
        const int length, short unsigned int* outWord) {
    int32_t newWord[MAX_WORD_LENGTH_INTERNAL];
    int depth = 0;
    int maxFreq = -1;
    const uint8_t* const root = DICT_ROOT;

    mStackChildCount[0] = root[0];
    mStackInputIndex[0] = 0;
    mStackSiblingPos[0] = 1;
    while (depth >= 0) {
        const int charGroupCount = mStackChildCount[depth];
        int pos = mStackSiblingPos[depth];
        for (int charGroupIndex = charGroupCount - 1; charGroupIndex >= 0; --charGroupIndex) {
            int inputIndex = mStackInputIndex[depth];
            const uint8_t flags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
            // Test whether all chars in this group match with the word we are searching for. If so,
            // we want to traverse its children (or if the length match, evaluate its frequency).
            // Note that this function will output the position regardless, but will only write
            // into inputIndex if there is a match.
            const bool isAlike = testCharGroupForContinuedLikeness(flags, root, pos, inWord,
                    inputIndex, newWord, &inputIndex, &pos);
            if (isAlike && (FLAG_IS_TERMINAL & flags) && (inputIndex == length)) {
                const int frequency = BinaryFormat::readFrequencyWithoutMovingPointer(root, pos);
                onTerminalWordLike(frequency, newWord, inputIndex, outWord, &maxFreq);
            }
            pos = BinaryFormat::skipFrequency(flags, pos);
            const int siblingPos = BinaryFormat::skipChildrenPosAndAttributes(root, flags, pos);
            const int childrenNodePos = BinaryFormat::readChildrenPosition(root, flags, pos);
            // If we had a match and the word has children, we want to traverse them. We don't have
            // to traverse words longer than the one we are searching for, since they will not match
            // anyway, so don't traverse unless inputIndex < length.
            if (isAlike && (-1 != childrenNodePos) && (inputIndex < length)) {
                // Save position for this depth, to get back to this once children are done
                mStackChildCount[depth] = charGroupIndex;
                mStackSiblingPos[depth] = siblingPos;
                // Prepare stack values for next depth
                ++depth;
                int childrenPos = childrenNodePos;
                mStackChildCount[depth] =
                        BinaryFormat::getGroupCountAndForwardPointer(root, &childrenPos);
                mStackSiblingPos[depth] = childrenPos;
                mStackInputIndex[depth] = inputIndex;
                pos = childrenPos;
                // Go to the next depth level.
                ++depth;
                break;
            } else {
                // No match, or no children, or word too long to ever match: go the next sibling.
                pos = siblingPos;
            }
        }
        --depth;
    }
    return maxFreq;
}

bool UnigramDictionary::isValidWord(const uint16_t* const inWord, const int length) const {
    return NOT_VALID_WORD != BinaryFormat::getTerminalPosition(DICT_ROOT, inWord, length);
}

// TODO: remove this function.
int UnigramDictionary::getBigramPosition(int pos, unsigned short *word, int offset,
        int length) const {
    return -1;
}

// ProcessCurrentNode returns a boolean telling whether to traverse children nodes or not.
// If the return value is false, then the caller should read in the output "nextSiblingPosition"
// to find out the address of the next sibling node and pass it to a new call of processCurrentNode.
// It is worthy to note that when false is returned, the output values other than
// nextSiblingPosition are undefined.
// If the return value is true, then the caller must proceed to traverse the children of this
// node. processCurrentNode will output the information about the children: their count in
// newCount, their position in newChildrenPosition, the traverseAllNodes flag in
// newTraverseAllNodes, the match weight into newMatchRate, the input index into newInputIndex, the
// diffs into newDiffs, the sibling position in nextSiblingPosition, and the output index into
// newOutputIndex. Please also note the following caveat: processCurrentNode does not know when
// there aren't any more nodes at this level, it merely returns the address of the first byte after
// the current node in nextSiblingPosition. Thus, the caller must keep count of the nodes at any
// given level, as output into newCount when traversing this level's parent.
inline bool UnigramDictionary::processCurrentNode(const int initialPos,
        Correction *correction, int *newCount,
        int *newChildrenPosition, int *nextSiblingPosition) {
    if (DEBUG_DICT) {
        correction->checkState();
    }
    int pos = initialPos;

    // Flags contain the following information:
    // - Address type (MASK_GROUP_ADDRESS_TYPE) on two bits:
    //   - FLAG_GROUP_ADDRESS_TYPE_{ONE,TWO,THREE}_BYTES means there are children and their address
    //     is on the specified number of bytes.
    //   - FLAG_GROUP_ADDRESS_TYPE_NOADDRESS means there are no children, and therefore no address.
    // - FLAG_HAS_MULTIPLE_CHARS: whether this node has multiple char or not.
    // - FLAG_IS_TERMINAL: whether this node is a terminal or not (it may still have children)
    // - FLAG_HAS_BIGRAMS: whether this node has bigrams or not
    const uint8_t flags = BinaryFormat::getFlagsAndForwardPointer(DICT_ROOT, &pos);
    const bool hasMultipleChars = (0 != (FLAG_HAS_MULTIPLE_CHARS & flags));
    const bool isTerminalNode = (0 != (FLAG_IS_TERMINAL & flags));

    bool needsToInvokeOnTerminal = false;

    // This gets only ONE character from the stream. Next there will be:
    // if FLAG_HAS_MULTIPLE CHARS: the other characters of the same node
    // else if FLAG_IS_TERMINAL: the frequency
    // else if MASK_GROUP_ADDRESS_TYPE is not NONE: the children address
    // Note that you can't have a node that both is not a terminal and has no children.
    int32_t c = BinaryFormat::getCharCodeAndForwardPointer(DICT_ROOT, &pos);
    assert(NOT_A_CHARACTER != c);

    // We are going to loop through each character and make it look like it's a different
    // node each time. To do that, we will process characters in this node in order until
    // we find the character terminator. This is signalled by getCharCode* returning
    // NOT_A_CHARACTER.
    // As a special case, if there is only one character in this node, we must not read the
    // next bytes so we will simulate the NOT_A_CHARACTER return by testing the flags.
    // This way, each loop run will look like a "virtual node".
    do {
        // We prefetch the next char. If 'c' is the last char of this node, we will have
        // NOT_A_CHARACTER in the next char. From this we can decide whether this virtual node
        // should behave as a terminal or not and whether we have children.
        const int32_t nextc = hasMultipleChars
                ? BinaryFormat::getCharCodeAndForwardPointer(DICT_ROOT, &pos) : NOT_A_CHARACTER;
        const bool isLastChar = (NOT_A_CHARACTER == nextc);
        // If there are more chars in this nodes, then this virtual node is not a terminal.
        // If we are on the last char, this virtual node is a terminal if this node is.
        const bool isTerminal = isLastChar && isTerminalNode;

        Correction::CorrectionType stateType = correction->processCharAndCalcState(
                c, isTerminal);
        if (stateType == Correction::TRAVERSE_ALL_ON_TERMINAL
                || stateType == Correction::ON_TERMINAL) {
            needsToInvokeOnTerminal = true;
        } else if (stateType == Correction::UNRELATED) {
            // We found that this is an unrelated character, so we should give up traversing
            // this node and its children entirely.
            // However we may not be on the last virtual node yet so we skip the remaining
            // characters in this node, the frequency if it's there, read the next sibling
            // position to output it, then return false.
            // We don't have to output other values because we return false, as in
            // "don't traverse children".
            if (!isLastChar) {
                pos = BinaryFormat::skipOtherCharacters(DICT_ROOT, pos);
            }
            pos = BinaryFormat::skipFrequency(flags, pos);
            *nextSiblingPosition =
                    BinaryFormat::skipChildrenPosAndAttributes(DICT_ROOT, flags, pos);
            return false;
        }

        // Prepare for the next character. Promote the prefetched char to current char - the loop
        // will take care of prefetching the next. If we finally found our last char, nextc will
        // contain NOT_A_CHARACTER.
        c = nextc;
    } while (NOT_A_CHARACTER != c);

    if (isTerminalNode) {
        if (needsToInvokeOnTerminal) {
            // The frequency should be here, because we come here only if this is actually
            // a terminal node, and we are on its last char.
            const int freq = BinaryFormat::readFrequencyWithoutMovingPointer(DICT_ROOT, pos);
            onTerminal(freq, mCorrection);
        }

        // If there are more chars in this node, then this virtual node has children.
        // If we are on the last char, this virtual node has children if this node has.
        const bool hasChildren = BinaryFormat::hasChildrenInFlags(flags);

        // This character matched the typed character (enough to traverse the node at least)
        // so we just evaluated it. Now we should evaluate this virtual node's children - that
        // is, if it has any. If it has no children, we're done here - so we skip the end of
        // the node, output the siblings position, and return false "don't traverse children".
        // Note that !hasChildren implies isLastChar, so we know we don't have to skip any
        // remaining char in this group for there can't be any.
        if (!hasChildren) {
            pos = BinaryFormat::skipFrequency(flags, pos);
            *nextSiblingPosition =
                    BinaryFormat::skipChildrenPosAndAttributes(DICT_ROOT, flags, pos);
            return false;
        }

        // Optimization: Prune out words that are too long compared to how much was typed.
        if (correction->needsToPrune()) {
            pos = BinaryFormat::skipFrequency(flags, pos);
            *nextSiblingPosition =
                    BinaryFormat::skipChildrenPosAndAttributes(DICT_ROOT, flags, pos);
            return false;
        }
    }

    // Now we finished processing this node, and we want to traverse children. If there are no
    // children, we can't come here.
    assert(BinaryFormat::hasChildrenInFlags(flags));

    // If this node was a terminal it still has the frequency under the pointer (it may have been
    // read, but not skipped - see readFrequencyWithoutMovingPointer).
    // Next come the children position, then possibly attributes (attributes are bigrams only for
    // now, maybe something related to shortcuts in the future).
    // Once this is read, we still need to output the number of nodes in the immediate children of
    // this node, so we read and output it before returning true, as in "please traverse children".
    pos = BinaryFormat::skipFrequency(flags, pos);
    int childrenPos = BinaryFormat::readChildrenPosition(DICT_ROOT, flags, pos);
    *nextSiblingPosition = BinaryFormat::skipChildrenPosAndAttributes(DICT_ROOT, flags, pos);
    *newCount = BinaryFormat::getGroupCountAndForwardPointer(DICT_ROOT, &childrenPos);
    *newChildrenPosition = childrenPos;
    return true;
}

} // namespace latinime