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Diffstat (limited to 'lm/filter/phrase.cc')
| -rw-r--r-- | lm/filter/phrase.cc | 281 |
1 files changed, 281 insertions, 0 deletions
diff --git a/lm/filter/phrase.cc b/lm/filter/phrase.cc new file mode 100644 index 000000000..1bef2a3f3 --- /dev/null +++ b/lm/filter/phrase.cc @@ -0,0 +1,281 @@ +#include "lm/filter/phrase.hh" + +#include "lm/filter/format.hh" + +#include <algorithm> +#include <functional> +#include <iostream> +#include <queue> +#include <string> +#include <vector> + +#include <ctype.h> + +namespace lm { +namespace phrase { + +unsigned int ReadMultiple(std::istream &in, Substrings &out) { + bool sentence_content = false; + unsigned int sentence_id = 0; + std::vector<Hash> phrase; + std::string word; + while (in) { + char c; + // Gather a word. + while (!isspace(c = in.get()) && in) word += c; + // Treat EOF like a newline. + if (!in) c = '\n'; + // Add the word to the phrase. + if (!word.empty()) { + phrase.push_back(util::MurmurHashNative(word.data(), word.size())); + word.clear(); + } + if (c == ' ') continue; + // It's more than just a space. Close out the phrase. + if (!phrase.empty()) { + sentence_content = true; + out.AddPhrase(sentence_id, phrase.begin(), phrase.end()); + phrase.clear(); + } + if (c == '\t' || c == '\v') continue; + // It's more than a space or tab: a newline. + if (sentence_content) { + ++sentence_id; + sentence_content = false; + } + } + if (!in.eof()) in.exceptions(std::istream::failbit | std::istream::badbit); + return sentence_id + sentence_content; +} + +namespace detail { const StringPiece kEndSentence("</s>"); } + +namespace { + +typedef unsigned int Sentence; +typedef std::vector<Sentence> Sentences; + +class Vertex; + +class Arc { + public: + Arc() {} + + // For arcs from one vertex to another. + void SetPhrase(Vertex &from, Vertex &to, const Sentences &intersect) { + Set(to, intersect); + from_ = &from; + } + + /* For arcs from before the n-gram begins to somewhere in the n-gram (right + * aligned). These have no from_ vertex; it implictly matches every + * sentence. This also handles when the n-gram is a substring of a phrase. + */ + void SetRight(Vertex &to, const Sentences &complete) { + Set(to, complete); + from_ = NULL; + } + + Sentence Current() const { + return *current_; + } + + bool Empty() const { + return current_ == last_; + } + + /* When this function returns: + * If Empty() then there's nothing left from this intersection. + * + * If Current() == to then to is part of the intersection. + * + * Otherwise, Current() > to. In this case, to is not part of the + * intersection and neither is anything < Current(). To determine if + * any value >= Current() is in the intersection, call LowerBound again + * with the value. + */ + void LowerBound(const Sentence to); + + private: + void Set(Vertex &to, const Sentences &sentences); + + const Sentence *current_; + const Sentence *last_; + Vertex *from_; +}; + +struct ArcGreater : public std::binary_function<const Arc *, const Arc *, bool> { + bool operator()(const Arc *first, const Arc *second) const { + return first->Current() > second->Current(); + } +}; + +class Vertex { + public: + Vertex() : current_(0) {} + + Sentence Current() const { + return current_; + } + + bool Empty() const { + return incoming_.empty(); + } + + void LowerBound(const Sentence to); + + private: + friend class Arc; + + void AddIncoming(Arc *arc) { + if (!arc->Empty()) incoming_.push(arc); + } + + unsigned int current_; + std::priority_queue<Arc*, std::vector<Arc*>, ArcGreater> incoming_; +}; + +void Arc::LowerBound(const Sentence to) { + current_ = std::lower_bound(current_, last_, to); + // If *current_ > to, don't advance from_. The intervening values of + // from_ may be useful for another one of its outgoing arcs. + if (!from_ || Empty() || (Current() > to)) return; + assert(Current() == to); + from_->LowerBound(to); + if (from_->Empty()) { + current_ = last_; + return; + } + assert(from_->Current() >= to); + if (from_->Current() > to) { + current_ = std::lower_bound(current_ + 1, last_, from_->Current()); + } +} + +void Arc::Set(Vertex &to, const Sentences &sentences) { + current_ = &*sentences.begin(); + last_ = &*sentences.end(); + to.AddIncoming(this); +} + +void Vertex::LowerBound(const Sentence to) { + if (Empty()) return; + // Union lower bound. + while (true) { + Arc *top = incoming_.top(); + if (top->Current() > to) { + current_ = top->Current(); + return; + } + // If top->Current() == to, we still need to verify that's an actual + // element and not just a bound. + incoming_.pop(); + top->LowerBound(to); + if (!top->Empty()) { + incoming_.push(top); + if (top->Current() == to) { + current_ = to; + return; + } + } else if (Empty()) { + return; + } + } +} + +void BuildGraph(const Substrings &phrase, const std::vector<Hash> &hashes, Vertex *const vertices, Arc *free_arc) { + assert(!hashes.empty()); + + const Hash *const first_word = &*hashes.begin(); + const Hash *const last_word = &*hashes.end() - 1; + + Hash hash = 0; + const Sentences *found; + // Phrases starting at or before the first word in the n-gram. + { + Vertex *vertex = vertices; + for (const Hash *word = first_word; ; ++word, ++vertex) { + hash = util::MurmurHashNative(&hash, sizeof(uint64_t), *word); + // Now hash is [hashes.begin(), word]. + if (word == last_word) { + if (phrase.FindSubstring(hash, found)) + (free_arc++)->SetRight(*vertex, *found); + break; + } + if (!phrase.FindRight(hash, found)) break; + (free_arc++)->SetRight(*vertex, *found); + } + } + + // Phrases starting at the second or later word in the n-gram. + Vertex *vertex_from = vertices; + for (const Hash *word_from = first_word + 1; word_from != &*hashes.end(); ++word_from, ++vertex_from) { + hash = 0; + Vertex *vertex_to = vertex_from + 1; + for (const Hash *word_to = word_from; ; ++word_to, ++vertex_to) { + // Notice that word_to and vertex_to have the same index. + hash = util::MurmurHashNative(&hash, sizeof(uint64_t), *word_to); + // Now hash covers [word_from, word_to]. + if (word_to == last_word) { + if (phrase.FindLeft(hash, found)) + (free_arc++)->SetPhrase(*vertex_from, *vertex_to, *found); + break; + } + if (!phrase.FindPhrase(hash, found)) break; + (free_arc++)->SetPhrase(*vertex_from, *vertex_to, *found); + } + } +} + +} // namespace + +namespace detail { + +} // namespace detail + +bool Union::Evaluate() { + assert(!hashes_.empty()); + // Usually there are at most 6 words in an n-gram, so stack allocation is reasonable. + Vertex vertices[hashes_.size()]; + // One for every substring. + Arc arcs[((hashes_.size() + 1) * hashes_.size()) / 2]; + BuildGraph(substrings_, hashes_, vertices, arcs); + Vertex &last_vertex = vertices[hashes_.size() - 1]; + + unsigned int lower = 0; + while (true) { + last_vertex.LowerBound(lower); + if (last_vertex.Empty()) return false; + if (last_vertex.Current() == lower) return true; + lower = last_vertex.Current(); + } +} + +template <class Output> void Multiple::Evaluate(const StringPiece &line, Output &output) { + assert(!hashes_.empty()); + // Usually there are at most 6 words in an n-gram, so stack allocation is reasonable. + Vertex vertices[hashes_.size()]; + // One for every substring. + Arc arcs[((hashes_.size() + 1) * hashes_.size()) / 2]; + BuildGraph(substrings_, hashes_, vertices, arcs); + Vertex &last_vertex = vertices[hashes_.size() - 1]; + + unsigned int lower = 0; + while (true) { + last_vertex.LowerBound(lower); + if (last_vertex.Empty()) return; + if (last_vertex.Current() == lower) { + output.SingleAddNGram(lower, line); + ++lower; + } else { + lower = last_vertex.Current(); + } + } +} + +template void Multiple::Evaluate<CountFormat::Multiple>(const StringPiece &line, CountFormat::Multiple &output); +template void Multiple::Evaluate<ARPAFormat::Multiple>(const StringPiece &line, ARPAFormat::Multiple &output); +template void Multiple::Evaluate<MultipleOutputBuffer>(const StringPiece &line, MultipleOutputBuffer &output); + +} // namespace phrase +} // namespace lm |