From 3d1ed02a4e5d81aace80b0e004e96351d116630f Mon Sep 17 00:00:00 2001
From: Kenneth Heafield <github@kheafield.com>
Date: Tue, 18 Oct 2011 10:25:56 +0100
Subject: Revised <s> and </s> handling

---
 decoder/ff_klm.cc | 84 ++++++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 58 insertions(+), 26 deletions(-)

(limited to 'decoder')

diff --git a/decoder/ff_klm.cc b/decoder/ff_klm.cc
index 658aef80..3c941fbf 100644
--- a/decoder/ff_klm.cc
+++ b/decoder/ff_klm.cc
@@ -12,8 +12,8 @@
 #include "lm/model.hh"
 #include "lm/enumerate_vocab.hh"
 
+#define NEW_KENLM
 #undef NEW_KENLM
-#ifdef NEW_KENLM
 
 #include "lm/left.hh"
 
@@ -95,14 +95,58 @@ struct BoundaryAnnotatedState {
 
 #pragma pack(pop)
 
-void BoundaryCheck(bool &annotated, bool sub, double &ret) {
-  if (!sub) return;
-  if (annotated) {
-    ret -= 100.0;
-  } else {
-    annotated = true;
-  }
-}
+template <class Model> class BoundaryRuleScore {
+  public:
+    BoundaryRuleScore(const Model &m, BoundaryAnnotatedState &state) : 
+        back_(m, state.state),
+        bos_(state.seen_bos),
+        eos_(state.seen_eos),
+        penalty_(0.0),
+        end_sentence_(m.GetVocabulary().EndSentence()) {
+      bos_ = false;
+      eos_ = false;
+    }
+
+    void BeginSentence() {
+      back_.BeginSentence();
+      bos_ = true;
+    }
+
+    void BeginNonTerminal(const BoundaryAnnotatedState &sub) {
+      back_.BeginNonTerminal(sub.state, 0.0f);
+      bos_ = sub.seen_bos;
+      eos_ = sub.seen_eos;
+    }
+
+    void NonTerminal(const BoundaryAnnotatedState &sub) {
+      back_.NonTerminal(sub.state, 0.0f);
+      // cdec only calls this if there's content.  
+      if (sub.seen_bos) {
+        bos_ = true;
+        penalty_ -= 100.0f;
+      }
+      if (eos_) penalty_ -= 100.0f;
+      eos_ |= sub.seen_eos;
+    }
+
+    void Terminal(lm::WordIndex word) {
+      back_.Terminal(word);
+      if (eos_) penalty_ -= 100.0f;
+      if (word == end_sentence_) eos_ = true;
+    }
+
+    float Finish() {
+      return penalty_ + back_.Finish();
+    }
+
+  private:
+    lm::ngram::RuleScore<Model> back_;
+    bool &bos_, &eos_;
+
+    float penalty_;
+
+    lm::WordIndex end_sentence_;
+};
 
 } // namespace
 
@@ -112,42 +156,30 @@ class KLanguageModelImpl {
   double LookupWords(const TRule& rule, const vector<const void*>& ant_states, double* oovs, void* remnant) {
     *oovs = 0;
     const vector<WordID>& e = rule.e();
-    BoundaryAnnotatedState &annotated = *static_cast<BoundaryAnnotatedState*>(remnant);
-    lm::ngram::RuleScore<Model> ruleScore(*ngram_, annotated.state);
-    annotated.seen_bos = false;
-    annotated.seen_eos = false;
+    BoundaryRuleScore<Model> ruleScore(*ngram_, *static_cast<BoundaryAnnotatedState*>(remnant));
     unsigned i = 0;
-    double ret = 0.0;
     if (e.size()) {
       if (e[i] == kCDEC_SOS) {
         ++i;
         ruleScore.BeginSentence();
-        annotated.seen_bos = true;
       } else if (e[i] <= 0) {  // special case for left-edge NT
-        const BoundaryAnnotatedState &sub = *static_cast<const BoundaryAnnotatedState*>(ant_states[-e[0]]);
-        ruleScore.BeginNonTerminal(sub.state, 0.0f);
-        annotated.seen_bos = sub.seen_bos;
-        annotated.seen_eos = sub.seen_eos;
+        ruleScore.BeginNonTerminal(*static_cast<const BoundaryAnnotatedState*>(ant_states[-e[0]]));
         ++i;
       }
     }
     for (; i < e.size(); ++i) {
       if (e[i] <= 0) {
-        const BoundaryAnnotatedState &sub = *static_cast<const BoundaryAnnotatedState*>(ant_states[-e[i]]);
-        ruleScore.NonTerminal(sub.state, 0.0f);
-        BoundaryCheck(annotated.seen_bos, sub.seen_bos, ret);
-        BoundaryCheck(annotated.seen_eos, sub.seen_eos, ret);
+        ruleScore.NonTerminal(*static_cast<const BoundaryAnnotatedState*>(ant_states[-e[i]]));
       } else {
         const WordID cdec_word_or_class = ClassifyWordIfNecessary(e[i]);  // in future,
                                                                           // maybe handle emission
         const lm::WordIndex cur_word = MapWord(cdec_word_or_class); // map to LM's id
         if (cur_word == 0) (*oovs) += 1.0;
-        BoundaryCheck(annotated.seen_eos, cur_word == kEOS_, ret);
         ruleScore.Terminal(cur_word);
       }
     }
-    ret += ruleScore.Finish();
-    annotated.state.ZeroRemaining();
+    double ret = ruleScore.Finish();
+    static_cast<BoundaryAnnotatedState*>(remnant)->state.ZeroRemaining();
     return ret;
   }
 
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