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Diffstat (limited to 'lm/filter/phrase.hh')
-rw-r--r-- | lm/filter/phrase.hh | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/lm/filter/phrase.hh b/lm/filter/phrase.hh new file mode 100644 index 000000000..07479dea6 --- /dev/null +++ b/lm/filter/phrase.hh @@ -0,0 +1,153 @@ +#ifndef LM_FILTER_PHRASE_H__ +#define LM_FILTER_PHRASE_H__ + +#include "util/murmur_hash.hh" +#include "util/string_piece.hh" +#include "util/tokenize_piece.hh" + +#include <boost/unordered_map.hpp> + +#include <iosfwd> +#include <vector> + +#define LM_FILTER_PHRASE_METHOD(caps, lower) \ +bool Find##caps(Hash key, const std::vector<unsigned int> *&out) const {\ + Table::const_iterator i(table_.find(key));\ + if (i==table_.end()) return false; \ + out = &i->second.lower; \ + return true; \ +} + +namespace lm { +namespace phrase { + +typedef uint64_t Hash; + +class Substrings { + private: + /* This is the value in a hash table where the key is a string. It indicates + * four sets of sentences: + * substring is sentences with a phrase containing the key as a substring. + * left is sentencess with a phrase that begins with the key (left aligned). + * right is sentences with a phrase that ends with the key (right aligned). + * phrase is sentences where the key is a phrase. + * Each set is encoded as a vector of sentence ids in increasing order. + */ + struct SentenceRelation { + std::vector<unsigned int> substring, left, right, phrase; + }; + /* Most of the CPU is hash table lookups, so let's not complicate it with + * vector equality comparisons. If a collision happens, the SentenceRelation + * structure will contain the union of sentence ids over the colliding strings. + * In that case, the filter will be slightly more permissive. + * The key here is the same as boost's hash of std::vector<std::string>. + */ + typedef boost::unordered_map<Hash, SentenceRelation> Table; + + public: + Substrings() {} + + /* If the string isn't a substring of any phrase, return NULL. Otherwise, + * return a pointer to std::vector<unsigned int> listing sentences with + * matching phrases. This set may be empty for Left, Right, or Phrase. + * Example: const std::vector<unsigned int> *FindSubstring(Hash key) + */ + LM_FILTER_PHRASE_METHOD(Substring, substring) + LM_FILTER_PHRASE_METHOD(Left, left) + LM_FILTER_PHRASE_METHOD(Right, right) + LM_FILTER_PHRASE_METHOD(Phrase, phrase) + + // sentence_id must be non-decreasing. Iterators are over words in the phrase. + template <class Iterator> void AddPhrase(unsigned int sentence_id, const Iterator &begin, const Iterator &end) { + // Iterate over all substrings. + for (Iterator start = begin; start != end; ++start) { + Hash hash = 0; + SentenceRelation *relation; + for (Iterator finish = start; finish != end; ++finish) { + hash = util::MurmurHashNative(&hash, sizeof(uint64_t), *finish); + // Now hash is of [start, finish]. + relation = &table_[hash]; + AppendSentence(relation->substring, sentence_id); + if (start == begin) AppendSentence(relation->left, sentence_id); + } + AppendSentence(relation->right, sentence_id); + if (start == begin) AppendSentence(relation->phrase, sentence_id); + } + } + + private: + void AppendSentence(std::vector<unsigned int> &vec, unsigned int sentence_id) { + if (vec.empty() || vec.back() != sentence_id) vec.push_back(sentence_id); + } + + Table table_; +}; + +// Read a file with one sentence per line containing tab-delimited phrases of +// space-separated words. +unsigned int ReadMultiple(std::istream &in, Substrings &out); + +namespace detail { +extern const StringPiece kEndSentence; + +template <class Iterator> void MakeHashes(Iterator i, const Iterator &end, std::vector<Hash> &hashes) { + hashes.clear(); + if (i == end) return; + // TODO: check strict phrase boundaries after <s> and before </s>. For now, just skip tags. + if ((i->data()[0] == '<') && (i->data()[i->size() - 1] == '>')) { + ++i; + } + for (; i != end && (*i != kEndSentence); ++i) { + hashes.push_back(util::MurmurHashNative(i->data(), i->size())); + } +} + +} // namespace detail + +class Union { + public: + explicit Union(const Substrings &substrings) : substrings_(substrings) {} + + template <class Iterator> bool PassNGram(const Iterator &begin, const Iterator &end) { + detail::MakeHashes(begin, end, hashes_); + return hashes_.empty() || Evaluate(); + } + + private: + bool Evaluate(); + + std::vector<Hash> hashes_; + + const Substrings &substrings_; +}; + +class Multiple { + public: + explicit Multiple(const Substrings &substrings) : substrings_(substrings) {} + + template <class Iterator, class Output> void AddNGram(const Iterator &begin, const Iterator &end, const StringPiece &line, Output &output) { + detail::MakeHashes(begin, end, hashes_); + if (hashes_.empty()) { + output.AddNGram(line); + return; + } + Evaluate(line, output); + } + + template <class Output> void AddNGram(const StringPiece &ngram, const StringPiece &line, Output &output) { + AddNGram(util::TokenIter<util::SingleCharacter, true>(ngram, ' '), util::TokenIter<util::SingleCharacter, true>::end(), line, output); + } + + void Flush() const {} + + private: + template <class Output> void Evaluate(const StringPiece &line, Output &output); + + std::vector<Hash> hashes_; + + const Substrings &substrings_; +}; + +} // namespace phrase +} // namespace lm +#endif // LM_FILTER_PHRASE_H__ |