From e624824fb515d90d264a583eaa3fa00a8f6b6b51 Mon Sep 17 00:00:00 2001
From: Chris Dyer <cdyer@cs.cmu.edu>
Date: Mon, 13 Dec 2010 21:40:08 -0500
Subject: integration complete with KenLM, not fully tested

---
 decoder/ff_klm.cc | 297 ++++++++++++++++++++----------------------------------
 1 file changed, 107 insertions(+), 190 deletions(-)

(limited to 'decoder/ff_klm.cc')

diff --git a/decoder/ff_klm.cc b/decoder/ff_klm.cc
index 5888c4a3..092c07b0 100644
--- a/decoder/ff_klm.cc
+++ b/decoder/ff_klm.cc
@@ -1,5 +1,7 @@
 #include "ff_klm.h"
 
+#include <cstring>
+
 #include "hg.h"
 #include "tdict.h"
 #include "lm/model.hh"
@@ -24,217 +26,116 @@ struct VMapper : public lm::ngram::EnumerateVocab {
 };
 
 class KLanguageModelImpl {
-  inline int StateSize(const void* state) const {
-    return *(static_cast<const char*>(state) + state_size_);
-  }
-
-  inline void SetStateSize(int size, void* state) const {
-    *(static_cast<char*>(state) + state_size_) = size;
-  }
 
-#if 0
-  virtual double WordProb(WordID word, WordID const* context) {
-    return ngram_.wordProb(word, (VocabIndex*)context);
+  // returns the number of unscored words at the left edge of a span
+  inline int UnscoredSize(const void* state) const {
+    return *(static_cast<const char*>(state) + unscored_size_offset_);
   }
 
-  // may be shorter than actual null-terminated length.  context must be null terminated.  len is just to save effort for subclasses that don't support contextID
-  virtual int ContextSize(WordID const* context,int len) {
-    unsigned ret;
-    ngram_.contextID((VocabIndex*)context,ret);
-    return ret;
-  }
-  virtual double ContextBOW(WordID const* context,int shortened_len) {
-    return ngram_.contextBOW((VocabIndex*)context,shortened_len);
+  inline void SetUnscoredSize(int size, void* state) const {
+    *(static_cast<char*>(state) + unscored_size_offset_) = size;
   }
 
-  inline double LookupProbForBufferContents(int i) {
-//    int k = i; cerr << "P("; while(buffer_[k] > 0) { std::cerr << TD::Convert(buffer_[k++]) << " "; }
-    double p = WordProb(buffer_[i], &buffer_[i+1]);
-    if (p < floor_) p = floor_;
-//    cerr << ")=" << p << endl;
-    return p;
+  static inline const lm::ngram::Model::State& RemnantLMState(const void* state) {
+    return *static_cast<const lm::ngram::Model::State*>(state);
   }
 
-  string DebugStateToString(const void* state) const {
-    int len = StateSize(state);
-    const int* astate = reinterpret_cast<const int*>(state);
-    string res = "[";
-    for (int i = 0; i < len; ++i) {
-      res += " ";
-      res += TD::Convert(astate[i]);
-    }
-    res += " ]";
-    return res;
+  inline void SetRemnantLMState(const lm::ngram::Model::State& lmstate, void* state) const {
+    // if we were clever, we could use the memory pointed to by state to do all
+    // the work, avoiding this copy
+    memcpy(state, &lmstate, ngram_->StateSize());
   }
 
-  inline double ProbNoRemnant(int i, int len) {
-    int edge = len;
-    bool flag = true;
-    double sum = 0.0;
-    while (i >= 0) {
-      if (buffer_[i] == kSTAR) {
-        edge = i;
-        flag = false;
-      } else if (buffer_[i] <= 0) {
-        edge = i;
-        flag = true;
-      } else {
-        if ((edge-i >= order_) || (flag && !(i == (len-1) && buffer_[i] == kSTART)))
-          sum += LookupProbForBufferContents(i);
-      }
-      --i;
-    }
-    return sum;
+  lm::WordIndex IthUnscoredWord(int i, const void* state) const {
+    const lm::WordIndex* const mem = reinterpret_cast<const lm::WordIndex*>(static_cast<const char*>(state) + unscored_words_offset_);
+    return mem[i];
   }
 
-  double EstimateProb(const vector<WordID>& phrase) {
-    int len = phrase.size();
-    buffer_.resize(len + 1);
-    buffer_[len] = kNONE;
-    int i = len - 1;
-    for (int j = 0; j < len; ++j,--i)
-      buffer_[i] = phrase[j];
-    return ProbNoRemnant(len - 1, len);
+  void SetIthUnscoredWord(int i, lm::WordIndex index, void *state) const {
+    lm::WordIndex* mem = reinterpret_cast<lm::WordIndex*>(static_cast<char*>(state) + unscored_words_offset_);
+    mem[i] = index;
   }
 
-  //TODO: make sure this doesn't get used in FinalTraversal, or if it does, that it causes no harm.
-
-  //TODO: use stateless_cost instead of ProbNoRemnant, check left words only.  for items w/ fewer words than ctx len, how are they represented?  kNONE padded?
-
-  //Vocab_None is (unsigned)-1 in srilm, same as kNONE. in srilm (-1), or that SRILM otherwise interprets -1 as a terminator and not a word
-  double EstimateProb(const void* state) {
-    if (unigram) return 0.;
-    int len = StateSize(state);
-    //  << "residual len: " << len << endl;
-    buffer_.resize(len + 1);
-    buffer_[len] = kNONE;
-    const int* astate = reinterpret_cast<const WordID*>(state);
-    int i = len - 1;
-    for (int j = 0; j < len; ++j,--i)
-      buffer_[i] = astate[j];
-    return ProbNoRemnant(len - 1, len);
-  }
-
-  //FIXME: this assumes no target words on final unary -> goal rule.  is that ok?
-  // for <s> (n-1 left words) and (n-1 right words) </s>
-  double FinalTraversalCost(const void* state) {
-    if (unigram) return 0.;
-    int slen = StateSize(state);
-    int len = slen + 2;
-    // cerr << "residual len: " << len << endl;
-    buffer_.resize(len + 1);
-    buffer_[len] = kNONE;
-    buffer_[len-1] = kSTART;
-    const int* astate = reinterpret_cast<const WordID*>(state);
-    int i = len - 2;
-    for (int j = 0; j < slen; ++j,--i)
-      buffer_[i] = astate[j];
-    buffer_[i] = kSTOP;
-    assert(i == 0);
-    return ProbNoRemnant(len - 1, len);
-  }
-
-  /// just how SRILM likes it: [rbegin,rend) is a phrase in reverse word order and null terminated so *rend=kNONE.  return unigram score for rend[-1] plus
-  /// cost returned is some kind of log prob (who cares, we're just adding)
-  double stateless_cost(WordID *rbegin,WordID *rend) {
-    UNIDBG("p(");
-    double sum=0;
-    for (;rend>rbegin;--rend) {
-      sum+=clamp(WordProb(rend[-1],rend));
-      UNIDBG(" "<<TD::Convert(rend[-1]));
-    }
-    UNIDBG(")="<<sum<<endl);
-    return sum;
+  bool HasFullContext(const void *state) const {
+    return *(static_cast<const char*>(state) + is_complete_offset_);
   }
 
-  //TODO: this would be a fine rule heuristic (for reordering hyperedges prior to rescoring.  for now you can just use a same-lm-file -o 1 prelm-rescore :(
-  double stateless_cost(TRule const& rule) {
-    //TODO: make sure this is correct.
-    int len = rule.ELength(); // use a gap for each variable
-    buffer_.resize(len + 1);
-    WordID * const rend=&buffer_[0]+len;
-    *rend=kNONE;
-    WordID *r=rend;  // append by *--r = x
-    const vector<WordID>& e = rule.e();
-    //SRILM is reverse order null terminated
-    //let's write down each phrase in reverse order and score it (note: we could lay them out consecutively then score them (we allocated enough buffer for that), but we won't actually use the whole buffer that way, since it wastes L1 cache.
-    double sum=0.;
-    for (unsigned j = 0; j < e.size(); ++j) {
-      if (e[j] < 1) { // variable
-        sum+=stateless_cost(r,rend);
-        r=rend;
-      } else { // terminal
-          *--r=e[j];
-      }
-    }
-    // last phrase (if any)
-    return sum+stateless_cost(r,rend);
+  void SetHasFullContext(bool flag, void *state) const {
+    *(static_cast<char*>(state) + is_complete_offset_) = flag;
   }
 
-  //NOTE: this is where the scoring of words happens (heuristic happens in EstimateProb)
-  double LookupWords(const TRule& rule, const vector<const void*>& ant_states, void* vstate) {
-    if (unigram)
-      return stateless_cost(rule);
+ public:
+  double LookupWords(const TRule& rule, const vector<const void*>& ant_states, double* pest_sum, void* remnant) {
+    double sum = 0.0;
+    double est_sum = 0.0;
     int len = rule.ELength() - rule.Arity();
-    for (int i = 0; i < ant_states.size(); ++i)
-      len += StateSize(ant_states[i]);
-    buffer_.resize(len + 1);
-    buffer_[len] = kNONE;
-    int i = len - 1;
+    int num_scored = 0;
+    int num_estimated = 0;
+    lm::ngram::Model::State state = ngram_->NullContextState();
     const vector<WordID>& e = rule.e();
+    bool context_complete = false;
     for (int j = 0; j < e.size(); ++j) {
       if (e[j] < 1) {
-        const int* astate = reinterpret_cast<const int*>(ant_states[-e[j]]);
-        int slen = StateSize(astate);
-        for (int k = 0; k < slen; ++k)
-          buffer_[i--] = astate[k];
+        const void* astate = (ant_states[-e[j]]);
+        int unscored_ant_len = UnscoredSize(astate);
+        for (int k = 0; k < unscored_ant_len; ++k) {
+          const lm::WordIndex cur_word = IthUnscoredWord(k, astate);
+          const lm::ngram::Model::State scopy(state);
+          const double p = ngram_->Score(scopy, cur_word, state);
+          ++num_scored;
+          if (!context_complete) {
+            if (num_scored >= order_) context_complete = true;
+          }
+          if (context_complete) {
+            sum += p;
+          } else {
+            if (remnant)
+              SetIthUnscoredWord(num_estimated, cur_word, remnant);
+            ++num_estimated;
+            est_sum += p;
+          }
+        }
+        if (HasFullContext(astate)) { // this is equivalent to the "star" in Chiang 2007
+          state = RemnantLMState(astate);
+          context_complete = true;
+        }
       } else {
-        buffer_[i--] = e[j];
+        const lm::WordIndex cur_word = MapWord(e[j]);
+        const lm::ngram::Model::State scopy(state);
+        const double p = ngram_->Score(scopy, cur_word, state);
+        ++num_scored;
+        if (!context_complete) {
+          if (num_scored >= order_) context_complete = true;
+        }
+        if (context_complete) {
+          sum += p;
+        } else {
+          if (remnant)
+            SetIthUnscoredWord(num_estimated, cur_word, remnant);
+          ++num_estimated;
+          est_sum += p;
+        }
       }
     }
-
-    double sum = 0.0;
-    int* remnant = reinterpret_cast<int*>(vstate);
-    int j = 0;
-    i = len - 1;
-    int edge = len;
-
-    while (i >= 0) {
-      if (buffer_[i] == kSTAR) {
-        edge = i;
-      } else if (edge-i >= order_) {
-        sum += LookupProbForBufferContents(i);
-      } else if (edge == len && remnant) {
-        remnant[j++] = buffer_[i];
-      }
-      --i;
+    if (pest_sum) *pest_sum = est_sum;
+    if (remnant) {
+      state.ZeroRemaining();
+      SetRemnantLMState(state, remnant);
+      SetUnscoredSize(num_estimated, remnant);
+      SetHasFullContext(context_complete || (num_scored >= order_), remnant);
     }
-    if (!remnant) return sum;
-
-    if (edge != len || len >= order_) {
-      remnant[j++] = kSTAR;
-      if (order_-1 < edge) edge = order_-1;
-      for (int i = edge-1; i >= 0; --i)
-        remnant[j++] = buffer_[i];
-    }
-
-    SetStateSize(j, vstate);
     return sum;
   }
 
-private:
-public:
-
- protected:
-  vector<WordID> buffer_;
- public:
-  WordID kSTART;
-  WordID kSTOP;
-  WordID kUNKNOWN;
-  WordID kNONE;
-  WordID kSTAR;
-  bool unigram;
-#endif
+  //FIXME: this assumes no target words on final unary -> goal rule.  is that ok?
+  // for <s> (n-1 left words) and (n-1 right words) </s>
+  double FinalTraversalCost(const void* state) {
+    SetRemnantLMState(ngram_->BeginSentenceState(), dummy_state_);
+    SetHasFullContext(1, dummy_state_);
+    SetUnscoredSize(0, dummy_state_);
+    dummy_ants_[1] = state;
+    return LookupWords(*dummy_rule_, dummy_ants_, NULL, NULL);
+  }
 
   lm::WordIndex MapWord(WordID w) const {
     if (w >= map_.size())
@@ -249,23 +150,38 @@ public:
     VMapper vm(&map_);
     conf.enumerate_vocab = &vm; 
     ngram_ = new lm::ngram::Model(param.c_str(), conf);
-    cerr << "Loaded " << order_ << "-gram KLM from " << param << endl;
     order_ = ngram_->Order();
-    state_size_ = ngram_->StateSize() + 1 + (order_-1) * sizeof(int);
+    cerr << "Loaded " << order_ << "-gram KLM from " << param << " (MapSize=" << map_.size() << ")\n";
+    state_size_ = ngram_->StateSize() + 2 + (order_ - 1) * sizeof(lm::WordIndex);
+    unscored_size_offset_ = ngram_->StateSize();
+    is_complete_offset_ = unscored_size_offset_ + 1;
+    unscored_words_offset_ = is_complete_offset_ + 1;
+
+    // special handling of beginning / ending sentence markers
+    dummy_state_ = new char[state_size_];
+    dummy_ants_.push_back(dummy_state_);
+    dummy_ants_.push_back(NULL);
+    dummy_rule_.reset(new TRule("[DUMMY] ||| [BOS] [DUMMY] ||| [1] [2] </s> ||| X=0"));
   }
 
   ~KLanguageModelImpl() {
     delete ngram_;
+    delete[] dummy_state_;
   }
 
-  const int ReserveStateSize() const { return state_size_; }
+  int ReserveStateSize() const { return state_size_; }
 
  private:
   lm::ngram::Model* ngram_;
   int order_;
   int state_size_;
+  int unscored_size_offset_;
+  int is_complete_offset_;
+  int unscored_words_offset_;
+  char* dummy_state_;
+  vector<const void*> dummy_ants_;
   vector<lm::WordIndex> map_;
-
+  TRulePtr dummy_rule_;
 };
 
 KLanguageModel::KLanguageModel(const string& param) {
@@ -288,12 +204,13 @@ void KLanguageModel::TraversalFeaturesImpl(const SentenceMetadata& /* smeta */,
                                           SparseVector<double>* features,
                                           SparseVector<double>* estimated_features,
                                           void* state) const {
-//  features->set_value(fid_, pimpl_->LookupWords(*edge.rule_, ant_states, state));
-//  estimated_features->set_value(fid_, imp().EstimateProb(state));
+  double est = 0;
+  features->set_value(fid_, pimpl_->LookupWords(*edge.rule_, ant_states, &est, state));
+  estimated_features->set_value(fid_, est);
 }
 
 void KLanguageModel::FinalTraversalFeatures(const void* ant_state,
                                            SparseVector<double>* features) const {
-//  features->set_value(fid_, imp().FinalTraversalCost(ant_state));
+  features->set_value(fid_, pimpl_->FinalTraversalCost(ant_state));
 }
 
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