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Add bigram lookup implementation. 

Bug: 5046459
Change-Id: Id2c7686c5da078751ed587e559417e808779aa7a
main
Jean Chalard 2011-07-25 14:03:19 +09:00
parent c1fd3cf50f
commit 588e2f2964
4 changed files with 195 additions and 162 deletions
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200
native/src/bigram_dictionary.cpp
View File

@ -21,13 +21,14 @@
#include "bigram_dictionary.h"
#include "dictionary.h"
#include "binary_format.h"
namespace latinime {
BigramDictionary::BigramDictionary(const unsigned char *dict, int maxWordLength,
int maxAlternatives, const bool isLatestDictVersion, const bool hasBigram,
Dictionary *parentDictionary)
: DICT(dict), MAX_WORD_LENGTH(maxWordLength),
: DICT(dict + NEW_DICTIONARY_HEADER_SIZE), MAX_WORD_LENGTH(maxWordLength),
MAX_ALTERNATIVES(maxAlternatives), IS_LATEST_DICT_VERSION(isLatestDictVersion),
HAS_BIGRAM(hasBigram), mParentDictionary(parentDictionary) {
if (DEBUG_DICT) {
@ -82,170 +83,65 @@ bool BigramDictionary::addWordBigram(unsigned short *word, int length, int frequ
return false;
}
int BigramDictionary::getBigramAddress(int *pos, bool advance) {
int address = 0;
address += (DICT[*pos] & 0x3F) << 16;
address += (DICT[*pos + 1] & 0xFF) << 8;
address += (DICT[*pos + 2] & 0xFF);
if (advance) {
*pos += 3;
}
return address;
}
int BigramDictionary::getBigramFreq(int *pos) {
int freq = DICT[(*pos)++] & FLAG_BIGRAM_FREQ;
return freq;
}
/* Parameters :
* prevWord: the word before, the one for which we need to look up bigrams.
* prevWordLength: its length.
* codes: what user typed, in the same format as for UnigramDictionary::getSuggestions.
* codesSize: the size of the codes array.
* bigramChars: an array for output, at the same format as outwords for getSuggestions.
* bigramFreq: an array to output frequencies.
* maxWordLength: the maximum size of a word.
* maxBigrams: the maximum number of bigrams fitting in the bigramChars array.
* maxAlteratives: unused.
* This method returns the number of bigrams this word has, for backward compatibility.
* Note: this is not the number of bigrams output in the array, which is the number of
* bigrams this word has WHOSE first letter also matches the letter the user typed.
* TODO: this may not be a sensible thing to do. It makes sense when the bigrams are
* used to match the first letter of the second word, but once the user has typed more
* and the bigrams are used to boost unigram result scores, it makes little sense to
* reduce their scope to the ones that match the first letter.
*/
int BigramDictionary::getBigrams(unsigned short *prevWord, int prevWordLength, int *codes,
int codesSize, unsigned short *bigramChars, int *bigramFreq, int maxWordLength,
int maxBigrams, int maxAlternatives) {
// TODO: remove unused arguments, and refrain from storing stuff in members of this class
// TODO: have "in" arguments before "out" ones, and make out args explicit in the name
mBigramFreq = bigramFreq;
mBigramChars = bigramChars;
mInputCodes = codes;
mInputLength = codesSize;
mMaxBigrams = maxBigrams;
if (HAS_BIGRAM && IS_LATEST_DICT_VERSION) {
int pos = mParentDictionary->getBigramPosition(prevWord, prevWordLength);
if (DEBUG_DICT) {
LOGI("Pos -> %d", pos);
}
if (pos < 0) {
return 0;
}
const uint8_t* const root = DICT;
int pos = BinaryFormat::getTerminalPosition(root, prevWord, prevWordLength);
if (NOT_VALID_WORD == pos) return 0;
const int flags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
if (0 == (flags & UnigramDictionary::FLAG_HAS_BIGRAMS)) return 0;
if (0 == (flags & UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS)) {
BinaryFormat::getCharCodeAndForwardPointer(root, &pos);
} else {
pos = BinaryFormat::skipOtherCharacters(root, pos);
}
pos = BinaryFormat::skipChildrenPosition(flags, pos);
pos = BinaryFormat::skipFrequency(flags, pos);
int bigramFlags;
int bigramCount = 0;
int bigramExist = (DICT[pos] & FLAG_BIGRAM_READ);
if (bigramExist > 0) {
int nextBigramExist = 1;
while (nextBigramExist > 0 && bigramCount < maxBigrams) {
int bigramAddress = getBigramAddress(&pos, true);
int frequency = (FLAG_BIGRAM_FREQ & DICT[pos]);
// search for all bigrams and store them
searchForTerminalNode(bigramAddress, frequency);
nextBigramExist = (DICT[pos++] & FLAG_BIGRAM_CONTINUED);
bigramCount++;
}
}
do {
bigramFlags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
uint16_t bigramBuffer[MAX_WORD_LENGTH];
const int bigramPos = BinaryFormat::getAttributeAddressAndForwardPointer(root, bigramFlags,
&pos);
const int length = BinaryFormat::getWordAtAddress(root, bigramPos, MAX_WORD_LENGTH,
bigramBuffer);
if (checkFirstCharacter(bigramBuffer)) {
const int frequency = UnigramDictionary::MASK_ATTRIBUTE_FREQUENCY & bigramFlags;
addWordBigram(bigramBuffer, length, frequency);
}
++bigramCount;
} while (0 != (UnigramDictionary::FLAG_ATTRIBUTE_HAS_NEXT & bigramFlags));
return bigramCount;
}
return 0;
}
void BigramDictionary::searchForTerminalNode(int addressLookingFor, int frequency) {
// track word with such address and store it in an array
unsigned short word[MAX_WORD_LENGTH];
int pos;
int followDownBranchAddress = DICTIONARY_HEADER_SIZE;
bool found = false;
char followingChar = ' ';
int depth = -1;
while(!found) {
bool followDownAddressSearchStop = false;
bool firstAddress = true;
bool haveToSearchAll = true;
if (depth < MAX_WORD_LENGTH && depth >= 0) {
word[depth] = (unsigned short) followingChar;
}
pos = followDownBranchAddress; // pos start at count
int count = DICT[pos] & 0xFF;
if (DEBUG_DICT) {
LOGI("count - %d",count);
}
pos++;
for (int i = 0; i < count; i++) {
// pos at data
pos++;
// pos now at flag
if (!getFirstBitOfByte(&pos)) { // non-terminal
if (!followDownAddressSearchStop) {
int addr = getBigramAddress(&pos, false);
if (addr > addressLookingFor) {
followDownAddressSearchStop = true;
if (firstAddress) {
firstAddress = false;
haveToSearchAll = true;
} else if (!haveToSearchAll) {
break;
}
} else {
followDownBranchAddress = addr;
followingChar = (char)(0xFF & DICT[pos-1]);
if (firstAddress) {
firstAddress = false;
haveToSearchAll = false;
}
}
}
pos += 3;
} else if (getFirstBitOfByte(&pos)) { // terminal
if (addressLookingFor == (pos-1)) { // found !!
depth++;
word[depth] = (0xFF & DICT[pos-1]);
found = true;
break;
}
if (getSecondBitOfByte(&pos)) { // address + freq (4 byte)
if (!followDownAddressSearchStop) {
int addr = getBigramAddress(&pos, false);
if (addr > addressLookingFor) {
followDownAddressSearchStop = true;
if (firstAddress) {
firstAddress = false;
haveToSearchAll = true;
} else if (!haveToSearchAll) {
break;
}
} else {
followDownBranchAddress = addr;
followingChar = (char)(0xFF & DICT[pos-1]);
if (firstAddress) {
firstAddress = false;
haveToSearchAll = true;
}
}
}
pos += 4;
} else { // freq only (2 byte)
pos += 2;
}
// skipping bigram
int bigramExist = (DICT[pos] & FLAG_BIGRAM_READ);
if (bigramExist > 0) {
int nextBigramExist = 1;
while (nextBigramExist > 0) {
pos += 3;
nextBigramExist = (DICT[pos++] & FLAG_BIGRAM_CONTINUED);
}
} else {
pos++;
}
}
}
depth++;
if (followDownBranchAddress == 0) {
if (DEBUG_DICT) {
LOGI("ERROR!!! Cannot find bigram!!");
}
break;
}
}
if (checkFirstCharacter(word)) {
addWordBigram(word, depth, frequency);
}
}
bool BigramDictionary::checkFirstCharacter(unsigned short *word) {
// Checks whether this word starts with same character or neighboring characters of

147
native/src/binary_format.h
View File

@ -50,6 +50,8 @@ public:
int *pos);
static int getTerminalPosition(const uint8_t* const root, const uint16_t* const inWord,
const int length);
static int getWordAtAddress(const uint8_t* const root, const int address, const int maxDepth,
uint16_t* outWord);
};
inline int BinaryFormat::detectFormat(const uint8_t* const dict) {
@ -290,6 +292,151 @@ inline int BinaryFormat::getTerminalPosition(const uint8_t* const root,
}
}
// This function searches for a terminal in the dictionary by its address.
// Due to the fact that words are ordered in the dictionary in a strict breadth-first order,
// it is possible to check for this with advantageous complexity. For each node, we search
// for groups with children and compare the children address with the address we look for.
// When we shoot the address we look for, it means the word we look for is in the children
// of the previous group. The only tricky part is the fact that if we arrive at the end of a
// node with the last group's children address still less than what we are searching for, we
// must descend the last group's children (for example, if the word we are searching for starts
// with a z, it's the last group of the root node, so all children addresses will be smaller
// than the address we look for, and we have to descend the z node).
/* Parameters :
* root: the dictionary buffer
* address: the byte position of the last chargroup of the word we are searching for (this is
* what is stored as the "bigram address" in each bigram)
* outword: an array to write the found word, with MAX_WORD_LENGTH size.
* Return value : the length of the word, of 0 if the word was not found.
*/
inline int BinaryFormat::getWordAtAddress(const uint8_t* const root, const int address,
const int maxDepth, uint16_t* outWord) {
int pos = 0;
int wordPos = 0;
// One iteration of the outer loop iterates through nodes. As stated above, we will only
// traverse nodes that are actually a part of the terminal we are searching, so each time
// we enter this loop we are one depth level further than last time.
// The only reason we count nodes is because we want to reduce the probability of infinite
// looping in case there is a bug. Since we know there is an upper bound to the depth we are
// supposed to traverse, it does not hurt to count iterations.
for (int loopCount = maxDepth; loopCount > 0; --loopCount) {
int lastCandidateGroupPos = 0;
// Let's loop through char groups in this node searching for either the terminal
// or one of its ascendants.
for (int charGroupCount = getGroupCountAndForwardPointer(root, &pos); charGroupCount > 0;
--charGroupCount) {
const int startPos = pos;
const uint8_t flags = getFlagsAndForwardPointer(root, &pos);
const int32_t character = getCharCodeAndForwardPointer(root, &pos);
if (address == startPos) {
// We found the address. Copy the rest of the word in the buffer and return
// the length.
outWord[wordPos] = character;
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
int32_t nextChar = getCharCodeAndForwardPointer(root, &pos);
// We count chars in order to avoid infinite loops if the file is broken or
// if there is some other bug
int charCount = maxDepth;
while (-1 != nextChar && --charCount > 0) {
outWord[++wordPos] = nextChar;
nextChar = getCharCodeAndForwardPointer(root, &pos);
}
}
return ++wordPos;
}
// We need to skip past this char group, so skip any remaining chars after the
// first and possibly the frequency.
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & flags) {
pos = skipOtherCharacters(root, pos);
}
pos = skipFrequency(flags, pos);
// The fact that this group has children is very important. Since we already know
// that this group does not match, if it has no children we know it is irrelevant
// to what we are searching for.
const bool hasChildren = (UnigramDictionary::FLAG_GROUP_ADDRESS_TYPE_NOADDRESS !=
(UnigramDictionary::MASK_GROUP_ADDRESS_TYPE & flags));
// We will write in `found' whether we have passed the children address we are
// searching for. For example if we search for "beer", the children of b are less
// than the address we are searching for and the children of c are greater. When we
// come here for c, we realize this is too big, and that we should descend b.
bool found;
if (hasChildren) {
// Here comes the tricky part. First, read the children position.
const int childrenPos = readChildrenPosition(root, flags, pos);
if (childrenPos > address) {
// If the children pos is greater than address, it means the previous chargroup,
// which address is stored in lastCandidateGroupPos, was the right one.
found = true;
} else if (1 >= charGroupCount) {
// However if we are on the LAST group of this node, and we have NOT shot the
// address we should descend THIS node. So we trick the lastCandidateGroupPos
// so that we will descend this node, not the previous one.
lastCandidateGroupPos = startPos;
found = true;
} else {
// Else, we should continue looking.
found = false;
}
} else {
// Even if we don't have children here, we could still be on the last group of this
// node. If this is the case, we should descend the last group that had children,
// and their address is already in lastCandidateGroup.
found = (1 >= charGroupCount);
}
if (found) {
// Okay, we found the group we should descend. Its address is in
// the lastCandidateGroupPos variable, so we just re-read it.
if (0 != lastCandidateGroupPos) {
const uint8_t lastFlags =
getFlagsAndForwardPointer(root, &lastCandidateGroupPos);
const int32_t lastChar =
getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
// We copy all the characters in this group to the buffer
outWord[wordPos] = lastChar;
if (UnigramDictionary::FLAG_HAS_MULTIPLE_CHARS & lastFlags) {
int32_t nextChar =
getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
int charCount = maxDepth;
while (-1 != nextChar && --charCount > 0) {
outWord[++wordPos] = nextChar;
nextChar = getCharCodeAndForwardPointer(root, &lastCandidateGroupPos);
}
}
++wordPos;
// Now we only need to branch to the children address. Skip the frequency if
// it's there, read pos, and break to resume the search at pos.
lastCandidateGroupPos = skipFrequency(lastFlags, lastCandidateGroupPos);
pos = readChildrenPosition(root, lastFlags, lastCandidateGroupPos);
break;
} else {
// Here is a little tricky part: we come here if we found out that all children
// addresses in this group are bigger than the address we are searching for.
// Should we conclude the word is not in the dictionary? No! It could still be
// one of the remaining chargroups in this node, so we have to keep looking in
// this node until we find it (or we realize it's not there either, in which
// case it's actually not in the dictionary). Pass the end of this group, ready
// to start the next one.
pos = skipChildrenPosAndAttributes(root, flags, pos);
}
} else {
// If we did not find it, we should record the last children address for the next
// iteration.
if (hasChildren) lastCandidateGroupPos = startPos;
// Now skip the end of this group (children pos and the attributes if any) so that
// our pos is after the end of this char group, at the start of the next one.
pos = skipChildrenPosAndAttributes(root, flags, pos);
}
}
}
// If we have looked through all the chargroups and found no match, the address is
// not the address of a terminal in this dictionary.
return 0;
}
} // namespace latinime
#endif // LATINIME_BINARY_FORMAT_H

8
native/src/dictionary.cpp
View File

@ -57,12 +57,4 @@ bool Dictionary::isValidWord(unsigned short *word, int length) {
return mUnigramDictionary->isValidWord(word, length);
}
int Dictionary::getBigramPosition(unsigned short *word, int length) {
if (IS_LATEST_DICT_VERSION) {
return mUnigramDictionary->getBigramPosition(DICTIONARY_HEADER_SIZE, word, 0, length);
} else {
return mUnigramDictionary->getBigramPosition(0, word, 0, length);
}
}
} // namespace latinime

2
native/src/dictionary.h
View File

@ -64,8 +64,6 @@ public:
const int pos, unsigned short *c, int *childrenPosition,
bool *terminal, int *freq);
static inline unsigned short toBaseLowerCase(unsigned short c);
// TODO: delete this
int getBigramPosition(unsigned short *word, int length);
private:
bool hasBigram();