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authorredpony <redpony@ec762483-ff6d-05da-a07a-a48fb63a330f>2010-10-18 23:24:01 +0000
committerredpony <redpony@ec762483-ff6d-05da-a07a-a48fb63a330f>2010-10-18 23:24:01 +0000
commite0ef743090038ee02d656cee11debd2246624ba0 (patch)
treee5e1d32402c8dcb490c574e24c087c56d4cc172e /klm/lm/ngram.cc
parent0c2514868f58bbfe422aa275e2905182cf2f57eb (diff)
kenneth's LM preliminary integration
git-svn-id: https://ws10smt.googlecode.com/svn/trunk@681 ec762483-ff6d-05da-a07a-a48fb63a330f
Diffstat (limited to 'klm/lm/ngram.cc')
-rw-r--r--klm/lm/ngram.cc522
1 files changed, 522 insertions, 0 deletions
diff --git a/klm/lm/ngram.cc b/klm/lm/ngram.cc
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+++ b/klm/lm/ngram.cc
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+#include "lm/ngram.hh"
+
+#include "lm/exception.hh"
+#include "util/file_piece.hh"
+#include "util/joint_sort.hh"
+#include "util/murmur_hash.hh"
+#include "util/probing_hash_table.hh"
+
+#include <algorithm>
+#include <functional>
+#include <numeric>
+#include <limits>
+#include <string>
+
+#include <cmath>
+#include <fcntl.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace lm {
+namespace ngram {
+
+size_t hash_value(const State &state) {
+ return util::MurmurHashNative(state.history_, sizeof(WordIndex) * state.valid_length_);
+}
+
+namespace detail {
+uint64_t HashForVocab(const char *str, std::size_t len) {
+ // This proved faster than Boost's hash in speed trials: total load time Murmur 67090000, Boost 72210000
+ // Chose to use 64A instead of native so binary format will be portable across 64 and 32 bit.
+ return util::MurmurHash64A(str, len, 0);
+}
+
+void Prob::SetBackoff(float to) {
+ UTIL_THROW(FormatLoadException, "Attempt to set backoff " << to << " for the highest order n-gram");
+}
+
+// Normally static initialization is a bad idea but MurmurHash is pure arithmetic, so this is ok.
+const uint64_t kUnknownHash = HashForVocab("<unk>", 5);
+// Sadly some LMs have <UNK>.
+const uint64_t kUnknownCapHash = HashForVocab("<UNK>", 5);
+
+} // namespace detail
+
+SortedVocabulary::SortedVocabulary() : begin_(NULL), end_(NULL) {}
+
+std::size_t SortedVocabulary::Size(std::size_t entries, float ignored) {
+ // Lead with the number of entries.
+ return sizeof(uint64_t) + sizeof(Entry) * entries;
+}
+
+void SortedVocabulary::Init(void *start, std::size_t allocated, std::size_t entries) {
+ assert(allocated >= Size(entries));
+ // Leave space for number of entries.
+ begin_ = reinterpret_cast<Entry*>(reinterpret_cast<uint64_t*>(start) + 1);
+ end_ = begin_;
+ saw_unk_ = false;
+}
+
+WordIndex SortedVocabulary::Insert(const StringPiece &str) {
+ uint64_t hashed = detail::HashForVocab(str);
+ if (hashed == detail::kUnknownHash || hashed == detail::kUnknownCapHash) {
+ saw_unk_ = true;
+ return 0;
+ }
+ end_->key = hashed;
+ ++end_;
+ // This is 1 + the offset where it was inserted to make room for unk.
+ return end_ - begin_;
+}
+
+bool SortedVocabulary::FinishedLoading(detail::ProbBackoff *reorder_vocab) {
+ util::JointSort(begin_, end_, reorder_vocab + 1);
+ SetSpecial(Index("<s>"), Index("</s>"), 0, end_ - begin_ + 1);
+ // Save size.
+ *(reinterpret_cast<uint64_t*>(begin_) - 1) = end_ - begin_;
+ return saw_unk_;
+}
+
+void SortedVocabulary::LoadedBinary() {
+ end_ = begin_ + *(reinterpret_cast<const uint64_t*>(begin_) - 1);
+ SetSpecial(Index("<s>"), Index("</s>"), 0, end_ - begin_ + 1);
+}
+
+namespace detail {
+
+template <class Search> MapVocabulary<Search>::MapVocabulary() {}
+
+template <class Search> void MapVocabulary<Search>::Init(void *start, std::size_t allocated, std::size_t entries) {
+ lookup_ = Lookup(start, allocated);
+ available_ = 1;
+ // Later if available_ != expected_available_ then we can throw UnknownMissingException.
+ saw_unk_ = false;
+}
+
+template <class Search> WordIndex MapVocabulary<Search>::Insert(const StringPiece &str) {
+ uint64_t hashed = HashForVocab(str);
+ // Prevent unknown from going into the table.
+ if (hashed == kUnknownHash || hashed == kUnknownCapHash) {
+ saw_unk_ = true;
+ return 0;
+ } else {
+ lookup_.Insert(Lookup::Packing::Make(hashed, available_));
+ return available_++;
+ }
+}
+
+template <class Search> bool MapVocabulary<Search>::FinishedLoading(ProbBackoff *reorder_vocab) {
+ lookup_.FinishedInserting();
+ SetSpecial(Index("<s>"), Index("</s>"), 0, available_);
+ return saw_unk_;
+}
+
+template <class Search> void MapVocabulary<Search>::LoadedBinary() {
+ lookup_.LoadedBinary();
+ SetSpecial(Index("<s>"), Index("</s>"), 0, available_);
+}
+
+/* All of the entropy is in low order bits and boost::hash does poorly with
+ * these. Odd numbers near 2^64 chosen by mashing on the keyboard. There is a
+ * stable point: 0. But 0 is <unk> which won't be queried here anyway.
+ */
+inline uint64_t CombineWordHash(uint64_t current, const WordIndex next) {
+ uint64_t ret = (current * 8978948897894561157ULL) ^ (static_cast<uint64_t>(next) * 17894857484156487943ULL);
+ return ret;
+}
+
+uint64_t ChainedWordHash(const WordIndex *word, const WordIndex *word_end) {
+ if (word == word_end) return 0;
+ uint64_t current = static_cast<uint64_t>(*word);
+ for (++word; word != word_end; ++word) {
+ current = CombineWordHash(current, *word);
+ }
+ return current;
+}
+
+bool IsEntirelyWhiteSpace(const StringPiece &line) {
+ for (size_t i = 0; i < static_cast<size_t>(line.size()); ++i) {
+ if (!isspace(line.data()[i])) return false;
+ }
+ return true;
+}
+
+void ReadARPACounts(util::FilePiece &in, std::vector<size_t> &number) {
+ number.clear();
+ StringPiece line;
+ if (!IsEntirelyWhiteSpace(line = in.ReadLine())) UTIL_THROW(FormatLoadException, "First line was \"" << line << "\" not blank");
+ if ((line = in.ReadLine()) != "\\data\\") UTIL_THROW(FormatLoadException, "second line was \"" << line << "\" not \\data\\.");
+ while (!IsEntirelyWhiteSpace(line = in.ReadLine())) {
+ if (line.size() < 6 || strncmp(line.data(), "ngram ", 6)) UTIL_THROW(FormatLoadException, "count line \"" << line << "\"doesn't begin with \"ngram \"");
+ // So strtol doesn't go off the end of line.
+ std::string remaining(line.data() + 6, line.size() - 6);
+ char *end_ptr;
+ unsigned long int length = std::strtol(remaining.c_str(), &end_ptr, 10);
+ if ((end_ptr == remaining.c_str()) || (length - 1 != number.size())) UTIL_THROW(FormatLoadException, "ngram count lengths should be consecutive starting with 1: " << line);
+ if (*end_ptr != '=') UTIL_THROW(FormatLoadException, "Expected = immediately following the first number in the count line " << line);
+ ++end_ptr;
+ const char *start = end_ptr;
+ long int count = std::strtol(start, &end_ptr, 10);
+ if (count < 0) UTIL_THROW(FormatLoadException, "Negative n-gram count " << count);
+ if (start == end_ptr) UTIL_THROW(FormatLoadException, "Couldn't parse n-gram count from " << line);
+ number.push_back(count);
+ }
+}
+
+void ReadNGramHeader(util::FilePiece &in, unsigned int length) {
+ StringPiece line;
+ while (IsEntirelyWhiteSpace(line = in.ReadLine())) {}
+ std::stringstream expected;
+ expected << '\\' << length << "-grams:";
+ if (line != expected.str()) UTIL_THROW(FormatLoadException, "Was expecting n-gram header " << expected.str() << " but got " << line << " instead.");
+}
+
+// Special unigram reader because unigram's data structure is different and because we're inserting vocab words.
+template <class Voc> void Read1Grams(util::FilePiece &f, const size_t count, Voc &vocab, ProbBackoff *unigrams) {
+ ReadNGramHeader(f, 1);
+ for (size_t i = 0; i < count; ++i) {
+ try {
+ float prob = f.ReadFloat();
+ if (f.get() != '\t') UTIL_THROW(FormatLoadException, "Expected tab after probability");
+ ProbBackoff &value = unigrams[vocab.Insert(f.ReadDelimited())];
+ value.prob = prob;
+ switch (f.get()) {
+ case '\t':
+ value.SetBackoff(f.ReadFloat());
+ if ((f.get() != '\n')) UTIL_THROW(FormatLoadException, "Expected newline after backoff");
+ break;
+ case '\n':
+ value.ZeroBackoff();
+ break;
+ default:
+ UTIL_THROW(FormatLoadException, "Expected tab or newline after unigram");
+ }
+ } catch(util::Exception &e) {
+ e << " in the " << i << "th 1-gram at byte " << f.Offset();
+ throw;
+ }
+ }
+ if (f.ReadLine().size()) UTIL_THROW(FormatLoadException, "Expected blank line after unigrams at byte " << f.Offset());
+}
+
+template <class Voc, class Store> void ReadNGrams(util::FilePiece &f, const unsigned int n, const size_t count, const Voc &vocab, Store &store) {
+ ReadNGramHeader(f, n);
+
+ // vocab ids of words in reverse order
+ WordIndex vocab_ids[n];
+ typename Store::Packing::Value value;
+ for (size_t i = 0; i < count; ++i) {
+ try {
+ value.prob = f.ReadFloat();
+ for (WordIndex *vocab_out = &vocab_ids[n-1]; vocab_out >= vocab_ids; --vocab_out) {
+ *vocab_out = vocab.Index(f.ReadDelimited());
+ }
+ uint64_t key = ChainedWordHash(vocab_ids, vocab_ids + n);
+
+ switch (f.get()) {
+ case '\t':
+ value.SetBackoff(f.ReadFloat());
+ if ((f.get() != '\n')) UTIL_THROW(FormatLoadException, "Expected newline after backoff");
+ break;
+ case '\n':
+ value.ZeroBackoff();
+ break;
+ default:
+ UTIL_THROW(FormatLoadException, "Expected tab or newline after n-gram");
+ }
+ store.Insert(Store::Packing::Make(key, value));
+ } catch(util::Exception &e) {
+ e << " in the " << i << "th " << n << "-gram at byte " << f.Offset();
+ throw;
+ }
+ }
+
+ if (f.ReadLine().size()) UTIL_THROW(FormatLoadException, "Expected blank line after " << n << "-grams at byte " << f.Offset());
+ store.FinishedInserting();
+}
+
+template <class Search, class VocabularyT> size_t GenericModel<Search, VocabularyT>::Size(const std::vector<size_t> &counts, const Config &config) {
+ if (counts.size() > kMaxOrder) UTIL_THROW(FormatLoadException, "This model has order " << counts.size() << ". Edit ngram.hh's kMaxOrder to at least this value and recompile.");
+ if (counts.size() < 2) UTIL_THROW(FormatLoadException, "This ngram implementation assumes at least a bigram model.");
+ size_t memory_size = VocabularyT::Size(counts[0], config.probing_multiplier);
+ memory_size += sizeof(ProbBackoff) * (counts[0] + 1); // +1 for hallucinate <unk>
+ for (unsigned char n = 2; n < counts.size(); ++n) {
+ memory_size += Middle::Size(counts[n - 1], config.probing_multiplier);
+ }
+ memory_size += Longest::Size(counts.back(), config.probing_multiplier);
+ return memory_size;
+}
+
+template <class Search, class VocabularyT> void GenericModel<Search, VocabularyT>::SetupMemory(char *base, const std::vector<size_t> &counts, const Config &config) {
+ char *start = base;
+ size_t allocated = VocabularyT::Size(counts[0], config.probing_multiplier);
+ vocab_.Init(start, allocated, counts[0]);
+ start += allocated;
+ unigram_ = reinterpret_cast<ProbBackoff*>(start);
+ start += sizeof(ProbBackoff) * (counts[0] + 1);
+ for (unsigned int n = 2; n < counts.size(); ++n) {
+ allocated = Middle::Size(counts[n - 1], config.probing_multiplier);
+ middle_.push_back(Middle(start, allocated));
+ start += allocated;
+ }
+ allocated = Longest::Size(counts.back(), config.probing_multiplier);
+ longest_ = Longest(start, allocated);
+ start += allocated;
+ if (static_cast<std::size_t>(start - base) != Size(counts, config)) UTIL_THROW(FormatLoadException, "The data structures took " << (start - base) << " but Size says they should take " << Size(counts, config));
+}
+
+const char kMagicBytes[] = "mmap lm http://kheafield.com/code format version 0\n\0";
+struct BinaryFileHeader {
+ char magic[sizeof(kMagicBytes)];
+ float zero_f, one_f, minus_half_f;
+ WordIndex one_word_index, max_word_index;
+ uint64_t one_uint64;
+
+ void SetToReference() {
+ std::memcpy(magic, kMagicBytes, sizeof(magic));
+ zero_f = 0.0; one_f = 1.0; minus_half_f = -0.5;
+ one_word_index = 1;
+ max_word_index = std::numeric_limits<WordIndex>::max();
+ one_uint64 = 1;
+ }
+};
+
+bool IsBinaryFormat(int fd, off_t size) {
+ if (size == util::kBadSize || (size <= static_cast<off_t>(sizeof(BinaryFileHeader)))) return false;
+ // Try reading the header.
+ util::scoped_mmap memory(mmap(NULL, sizeof(BinaryFileHeader), PROT_READ, MAP_FILE | MAP_PRIVATE, fd, 0), sizeof(BinaryFileHeader));
+ if (memory.get() == MAP_FAILED) return false;
+ BinaryFileHeader reference_header = BinaryFileHeader();
+ reference_header.SetToReference();
+ if (!memcmp(memory.get(), &reference_header, sizeof(BinaryFileHeader))) return true;
+ if (!memcmp(memory.get(), "mmap lm ", 8)) UTIL_THROW(FormatLoadException, "File looks like it should be loaded with mmap, but the test values don't match. Was it built on a different machine or with a different compiler?");
+ return false;
+}
+
+std::size_t Align8(std::size_t in) {
+ std::size_t off = in % 8;
+ if (!off) return in;
+ return in + 8 - off;
+}
+
+std::size_t TotalHeaderSize(unsigned int order) {
+ return Align8(sizeof(BinaryFileHeader) + 1 /* order */ + sizeof(uint64_t) * order /* counts */ + sizeof(float) /* probing multiplier */ + 1 /* search_tag */);
+}
+
+void ReadBinaryHeader(const void *from, off_t size, std::vector<size_t> &out, float &probing_multiplier, unsigned char &search_tag) {
+ const char *from_char = reinterpret_cast<const char*>(from);
+ if (size < static_cast<off_t>(1 + sizeof(BinaryFileHeader))) UTIL_THROW(FormatLoadException, "File too short to have count information.");
+ // Skip over the BinaryFileHeader which was read by IsBinaryFormat.
+ from_char += sizeof(BinaryFileHeader);
+ unsigned char order = *reinterpret_cast<const unsigned char*>(from_char);
+ if (size < static_cast<off_t>(TotalHeaderSize(order))) UTIL_THROW(FormatLoadException, "File too short to have full header.");
+ out.resize(static_cast<std::size_t>(order));
+ const uint64_t *counts = reinterpret_cast<const uint64_t*>(from_char + 1);
+ for (std::size_t i = 0; i < out.size(); ++i) {
+ out[i] = static_cast<std::size_t>(counts[i]);
+ }
+ const float *probing_ptr = reinterpret_cast<const float*>(counts + out.size());
+ probing_multiplier = *probing_ptr;
+ search_tag = *reinterpret_cast<const char*>(probing_ptr + 1);
+}
+
+void WriteBinaryHeader(void *to, const std::vector<size_t> &from, float probing_multiplier, char search_tag) {
+ BinaryFileHeader header = BinaryFileHeader();
+ header.SetToReference();
+ memcpy(to, &header, sizeof(BinaryFileHeader));
+ char *out = reinterpret_cast<char*>(to) + sizeof(BinaryFileHeader);
+ *reinterpret_cast<unsigned char*>(out) = static_cast<unsigned char>(from.size());
+ uint64_t *counts = reinterpret_cast<uint64_t*>(out + 1);
+ for (std::size_t i = 0; i < from.size(); ++i) {
+ counts[i] = from[i];
+ }
+ float *probing_ptr = reinterpret_cast<float*>(counts + from.size());
+ *probing_ptr = probing_multiplier;
+ *reinterpret_cast<char*>(probing_ptr + 1) = search_tag;
+}
+
+template <class Search, class VocabularyT> GenericModel<Search, VocabularyT>::GenericModel(const char *file, Config config) : mapped_file_(util::OpenReadOrThrow(file)) {
+ const off_t file_size = util::SizeFile(mapped_file_.get());
+
+ std::vector<size_t> counts;
+
+ if (IsBinaryFormat(mapped_file_.get(), file_size)) {
+ memory_.reset(util::MapForRead(file_size, config.prefault, mapped_file_.get()), file_size);
+
+ unsigned char search_tag;
+ ReadBinaryHeader(memory_.begin(), file_size, counts, config.probing_multiplier, search_tag);
+ if (config.probing_multiplier < 1.0) UTIL_THROW(FormatLoadException, "Binary format claims to have a probing multiplier of " << config.probing_multiplier << " which is < 1.0.");
+ if (search_tag != Search::kBinaryTag) UTIL_THROW(FormatLoadException, "The binary file has a different search strategy than the one requested.");
+ size_t memory_size = Size(counts, config);
+
+ char *start = reinterpret_cast<char*>(memory_.get()) + TotalHeaderSize(counts.size());
+ if (memory_size != static_cast<size_t>(memory_.end() - start)) UTIL_THROW(FormatLoadException, "The mmap file " << file << " has size " << file_size << " but " << (memory_size + TotalHeaderSize(counts.size())) << " was expected based on the number of counts and configuration.");
+
+ SetupMemory(start, counts, config);
+ vocab_.LoadedBinary();
+ for (typename std::vector<Middle>::iterator i = middle_.begin(); i != middle_.end(); ++i) {
+ i->LoadedBinary();
+ }
+ longest_.LoadedBinary();
+
+ } else {
+ if (config.probing_multiplier <= 1.0) UTIL_THROW(FormatLoadException, "probing multiplier must be > 1.0");
+
+ util::FilePiece f(file, mapped_file_.release(), config.messages);
+ ReadARPACounts(f, counts);
+ size_t memory_size = Size(counts, config);
+ char *start;
+
+ if (config.write_mmap) {
+ // Write out an mmap file.
+ util::MapZeroedWrite(config.write_mmap, TotalHeaderSize(counts.size()) + memory_size, mapped_file_, memory_);
+ WriteBinaryHeader(memory_.get(), counts, config.probing_multiplier, Search::kBinaryTag);
+ start = reinterpret_cast<char*>(memory_.get()) + TotalHeaderSize(counts.size());
+ } else {
+ memory_.reset(util::MapAnonymous(memory_size), memory_size);
+ start = reinterpret_cast<char*>(memory_.get());
+ }
+ SetupMemory(start, counts, config);
+ try {
+ LoadFromARPA(f, counts, config);
+ } catch (FormatLoadException &e) {
+ e << " in file " << file;
+ throw;
+ }
+ }
+
+ // g++ prints warnings unless these are fully initialized.
+ State begin_sentence = State();
+ begin_sentence.valid_length_ = 1;
+ begin_sentence.history_[0] = vocab_.BeginSentence();
+ begin_sentence.backoff_[0] = unigram_[begin_sentence.history_[0]].backoff;
+ State null_context = State();
+ null_context.valid_length_ = 0;
+ P::Init(begin_sentence, null_context, vocab_, counts.size());
+}
+
+template <class Search, class VocabularyT> void GenericModel<Search, VocabularyT>::LoadFromARPA(util::FilePiece &f, const std::vector<size_t> &counts, const Config &config) {
+ // Read the unigrams.
+ Read1Grams(f, counts[0], vocab_, unigram_);
+ bool saw_unk = vocab_.FinishedLoading(unigram_);
+ if (!saw_unk) {
+ switch(config.unknown_missing) {
+ case Config::THROW_UP:
+ {
+ SpecialWordMissingException e("<unk>");
+ e << " and configuration was set to throw if unknown is missing";
+ throw e;
+ }
+ case Config::COMPLAIN:
+ if (config.messages) *config.messages << "Language model is missing <unk>. Substituting probability " << config.unknown_missing_prob << "." << std::endl;
+ // There's no break;. This is by design.
+ case Config::SILENT:
+ // Default probabilities for unknown.
+ unigram_[0].backoff = 0.0;
+ unigram_[0].prob = config.unknown_missing_prob;
+ break;
+ }
+ }
+
+ // Read the n-grams.
+ for (unsigned int n = 2; n < counts.size(); ++n) {
+ ReadNGrams(f, n, counts[n-1], vocab_, middle_[n-2]);
+ }
+ ReadNGrams(f, counts.size(), counts[counts.size() - 1], vocab_, longest_);
+ if (std::fabs(unigram_[0].backoff) > 0.0000001) UTIL_THROW(FormatLoadException, "Backoff for unknown word should be zero, but was given as " << unigram_[0].backoff);
+}
+
+/* Ugly optimized function.
+ * in_state contains the previous ngram's length and backoff probabilites to
+ * be used here. out_state is populated with the found ngram length and
+ * backoffs that the next call will find useful.
+ *
+ * The search goes in increasing order of ngram length.
+ */
+template <class Search, class VocabularyT> FullScoreReturn GenericModel<Search, VocabularyT>::FullScore(
+ const State &in_state,
+ const WordIndex new_word,
+ State &out_state) const {
+
+ FullScoreReturn ret;
+ // This is end pointer passed to SumBackoffs.
+ const ProbBackoff &unigram = unigram_[new_word];
+ if (new_word == 0) {
+ ret.ngram_length = out_state.valid_length_ = 0;
+ // all of backoff.
+ ret.prob = std::accumulate(
+ in_state.backoff_,
+ in_state.backoff_ + in_state.valid_length_,
+ unigram.prob);
+ return ret;
+ }
+ float *backoff_out(out_state.backoff_);
+ *backoff_out = unigram.backoff;
+ ret.prob = unigram.prob;
+ out_state.history_[0] = new_word;
+ if (in_state.valid_length_ == 0) {
+ ret.ngram_length = out_state.valid_length_ = 1;
+ // No backoff because NGramLength() == 0 and unknown can't have backoff.
+ return ret;
+ }
+ ++backoff_out;
+
+ // Ok now we now that the bigram contains known words. Start by looking it up.
+
+ uint64_t lookup_hash = static_cast<uint64_t>(new_word);
+ const WordIndex *hist_iter = in_state.history_;
+ const WordIndex *const hist_end = hist_iter + in_state.valid_length_;
+ typename std::vector<Middle>::const_iterator mid_iter = middle_.begin();
+ for (; ; ++mid_iter, ++hist_iter, ++backoff_out) {
+ if (hist_iter == hist_end) {
+ // Used history [in_state.history_, hist_end) and ran out. No backoff.
+ std::copy(in_state.history_, hist_end, out_state.history_ + 1);
+ ret.ngram_length = out_state.valid_length_ = in_state.valid_length_ + 1;
+ // ret.prob was already set.
+ return ret;
+ }
+ lookup_hash = CombineWordHash(lookup_hash, *hist_iter);
+ if (mid_iter == middle_.end()) break;
+ typename Middle::ConstIterator found;
+ if (!mid_iter->Find(lookup_hash, found)) {
+ // Didn't find an ngram using hist_iter.
+ // The history used in the found n-gram is [in_state.history_, hist_iter).
+ std::copy(in_state.history_, hist_iter, out_state.history_ + 1);
+ // Therefore, we found a (hist_iter - in_state.history_ + 1)-gram including the last word.
+ ret.ngram_length = out_state.valid_length_ = (hist_iter - in_state.history_) + 1;
+ ret.prob = std::accumulate(
+ in_state.backoff_ + (mid_iter - middle_.begin()),
+ in_state.backoff_ + in_state.valid_length_,
+ ret.prob);
+ return ret;
+ }
+ *backoff_out = found->GetValue().backoff;
+ ret.prob = found->GetValue().prob;
+ }
+
+ typename Longest::ConstIterator found;
+ if (!longest_.Find(lookup_hash, found)) {
+ // It's an (P::Order()-1)-gram
+ std::copy(in_state.history_, in_state.history_ + P::Order() - 2, out_state.history_ + 1);
+ ret.ngram_length = out_state.valid_length_ = P::Order() - 1;
+ ret.prob += in_state.backoff_[P::Order() - 2];
+ return ret;
+ }
+ // It's an P::Order()-gram
+ // out_state.valid_length_ is still P::Order() - 1 because the next lookup will only need that much.
+ std::copy(in_state.history_, in_state.history_ + P::Order() - 2, out_state.history_ + 1);
+ out_state.valid_length_ = P::Order() - 1;
+ ret.ngram_length = P::Order();
+ ret.prob = found->GetValue().prob;
+ return ret;
+}
+
+template class GenericModel<ProbingSearch, MapVocabulary<ProbingSearch> >;
+template class GenericModel<SortedUniformSearch, SortedVocabulary>;
+} // namespace detail
+} // namespace ngram
+} // namespace lm