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/*
* Copyright (C) 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 <cstring>
#define LOG_TAG "LatinIME: bigram_dictionary.cpp"
#include "bigram_dictionary.h"
#include "binary_format.h"
#include "bloom_filter.h"
#include "defines.h"
#include "dictionary.h"
namespace latinime {
BigramDictionary::BigramDictionary(const unsigned char *dict, int maxWordLength, int maxPredictions)
: DICT(dict), MAX_WORD_LENGTH(maxWordLength), MAX_PREDICTIONS(maxPredictions) {
if (DEBUG_DICT) {
AKLOGI("BigramDictionary - constructor");
}
}
BigramDictionary::~BigramDictionary() {
}
bool BigramDictionary::addWordBigram(unsigned short *word, int length, int frequency,
int *bigramFreq, unsigned short *bigramChars, int *outputTypes) const {
word[length] = 0;
if (DEBUG_DICT) {
#ifdef FLAG_DBG
char s[length + 1];
for (int i = 0; i <= length; i++) s[i] = word[i];
AKLOGI("Bigram: Found word = %s, freq = %d :", s, frequency);
#endif
}
// Find the right insertion point
int insertAt = 0;
while (insertAt < MAX_PREDICTIONS) {
if (frequency > bigramFreq[insertAt] || (bigramFreq[insertAt] == frequency
&& length < Dictionary::wideStrLen(bigramChars + insertAt * MAX_WORD_LENGTH))) {
break;
}
insertAt++;
}
if (DEBUG_DICT) {
AKLOGI("Bigram: InsertAt -> %d MAX_PREDICTIONS: %d", insertAt, MAX_PREDICTIONS);
}
if (insertAt < MAX_PREDICTIONS) {
memmove(bigramFreq + (insertAt + 1),
bigramFreq + insertAt,
(MAX_PREDICTIONS - insertAt - 1) * sizeof(bigramFreq[0]));
bigramFreq[insertAt] = frequency;
outputTypes[insertAt] = Dictionary::KIND_PREDICTION;
memmove(bigramChars + (insertAt + 1) * MAX_WORD_LENGTH,
bigramChars + insertAt * MAX_WORD_LENGTH,
(MAX_PREDICTIONS - insertAt - 1) * sizeof(bigramChars[0]) * MAX_WORD_LENGTH);
unsigned short *dest = bigramChars + insertAt * MAX_WORD_LENGTH;
while (length--) {
*dest++ = *word++;
}
*dest = 0; // NULL terminate
if (DEBUG_DICT) {
AKLOGI("Bigram: Added word at %d", insertAt);
}
return true;
}
return false;
}
/* Parameters :
* prevWord: the word before, the one for which we need to look up bigrams.
* prevWordLength: its length.
* inputCodes: 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.
* outputTypes: an array to output types.
* 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(const int32_t *prevWord, int prevWordLength, int *inputCodes,
int codesSize, unsigned short *bigramChars, int *bigramFreq, int *outputTypes) const {
// 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
const uint8_t *const root = DICT;
int pos = getBigramListPositionForWord(prevWord, prevWordLength,
false /* forceLowerCaseSearch */);
// getBigramListPositionForWord returns 0 if this word isn't in the dictionary or has no bigrams
if (0 == pos) {
// If no bigrams for this exact word, search again in lower case.
pos = getBigramListPositionForWord(prevWord, prevWordLength,
true /* forceLowerCaseSearch */);
}
// If still no bigrams, we really don't have them!
if (0 == pos) return 0;
uint8_t bigramFlags;
int bigramCount = 0;
do {
bigramFlags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
uint16_t bigramBuffer[MAX_WORD_LENGTH];
int unigramFreq = 0;
const int bigramPos = BinaryFormat::getAttributeAddressAndForwardPointer(root, bigramFlags,
&pos);
const int length = BinaryFormat::getWordAtAddress(root, bigramPos, MAX_WORD_LENGTH,
bigramBuffer, &unigramFreq);
// codesSize == 0 means we are trying to find bigram predictions.
if (codesSize < 1 || checkFirstCharacter(bigramBuffer, inputCodes)) {
const int bigramFreqTemp = BinaryFormat::MASK_ATTRIBUTE_FREQUENCY & bigramFlags;
// Due to space constraints, the frequency for bigrams is approximate - the lower the
// unigram frequency, the worse the precision. The theoritical maximum error in
// resulting frequency is 8 - although in the practice it's never bigger than 3 or 4
// in very bad cases. This means that sometimes, we'll see some bigrams interverted
// here, but it can't get too bad.
const int frequency =
BinaryFormat::computeFrequencyForBigram(unigramFreq, bigramFreqTemp);
if (addWordBigram(bigramBuffer, length, frequency, bigramFreq, bigramChars,
outputTypes)) {
++bigramCount;
}
}
} while (BinaryFormat::FLAG_ATTRIBUTE_HAS_NEXT & bigramFlags);
return bigramCount;
}
// Returns a pointer to the start of the bigram list.
// If the word is not found or has no bigrams, this function returns 0.
int BigramDictionary::getBigramListPositionForWord(const int32_t *prevWord,
const int prevWordLength, const bool forceLowerCaseSearch) const {
if (0 >= prevWordLength) return 0;
const uint8_t *const root = DICT;
int pos = BinaryFormat::getTerminalPosition(root, prevWord, prevWordLength,
forceLowerCaseSearch);
if (NOT_VALID_WORD == pos) return 0;
const uint8_t flags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
if (0 == (flags & BinaryFormat::FLAG_HAS_BIGRAMS)) return 0;
if (0 == (flags & BinaryFormat::FLAG_HAS_MULTIPLE_CHARS)) {
BinaryFormat::getCodePointAndForwardPointer(root, &pos);
} else {
pos = BinaryFormat::skipOtherCharacters(root, pos);
}
pos = BinaryFormat::skipFrequency(flags, pos);
pos = BinaryFormat::skipChildrenPosition(flags, pos);
pos = BinaryFormat::skipShortcuts(root, flags, pos);
return pos;
}
void BigramDictionary::fillBigramAddressToFrequencyMapAndFilter(const int32_t *prevWord,
const int prevWordLength, std::map<int, int> *map, uint8_t *filter) const {
memset(filter, 0, BIGRAM_FILTER_BYTE_SIZE);
const uint8_t *const root = DICT;
int pos = getBigramListPositionForWord(prevWord, prevWordLength,
false /* forceLowerCaseSearch */);
if (0 == pos) {
// If no bigrams for this exact string, search again in lower case.
pos = getBigramListPositionForWord(prevWord, prevWordLength,
true /* forceLowerCaseSearch */);
}
if (0 == pos) return;
uint8_t bigramFlags;
do {
bigramFlags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
const int frequency = BinaryFormat::MASK_ATTRIBUTE_FREQUENCY & bigramFlags;
const int bigramPos = BinaryFormat::getAttributeAddressAndForwardPointer(root, bigramFlags,
&pos);
(*map)[bigramPos] = frequency;
setInFilter(filter, bigramPos);
} while (0 != (BinaryFormat::FLAG_ATTRIBUTE_HAS_NEXT & bigramFlags));
}
bool BigramDictionary::checkFirstCharacter(unsigned short *word, int *inputCodes) const {
// Checks whether this word starts with same character or neighboring characters of
// what user typed.
int maxAlt = MAX_ALTERNATIVES;
const unsigned short firstBaseChar = toBaseLowerCase(*word);
while (maxAlt > 0) {
if (toBaseLowerCase(*inputCodes) == firstBaseChar) {
return true;
}
inputCodes++;
maxAlt--;
}
return false;
}
bool BigramDictionary::isValidBigram(const int32_t *word1, int length1, const int32_t *word2,
int length2) const {
const uint8_t *const root = DICT;
int pos = getBigramListPositionForWord(word1, length1, false /* forceLowerCaseSearch */);
// getBigramListPositionForWord returns 0 if this word isn't in the dictionary or has no bigrams
if (0 == pos) return false;
int nextWordPos = BinaryFormat::getTerminalPosition(root, word2, length2,
false /* forceLowerCaseSearch */);
if (NOT_VALID_WORD == nextWordPos) return false;
uint8_t bigramFlags;
do {
bigramFlags = BinaryFormat::getFlagsAndForwardPointer(root, &pos);
const int bigramPos = BinaryFormat::getAttributeAddressAndForwardPointer(root, bigramFlags,
&pos);
if (bigramPos == nextWordPos) {
return true;
}
} while (BinaryFormat::FLAG_ATTRIBUTE_HAS_NEXT & bigramFlags);
return false;
}
// TODO: Move functions related to bigram to here
} // namespace latinime
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