3 files changed, 80 insertions, 0 deletions

diff --git a/decoder/cdec_ff.cc b/decoder/cdec_ff.cc
index e87ab5ab..729d1214 100644
--- a/decoder/cdec_ff.cc
+++ b/decoder/cdec_ff.cc
@@ -60,6 +60,7 @@ void register_feature_functions() {
   ff_registry.Register("Tagger_BigramIdentity", new FFFactory<Tagger_BigramIdentity>);
   ff_registry.Register("LexicalPairIdentity", new FFFactory<LexicalPairIdentity>);
   ff_registry.Register("OutputIdentity", new FFFactory<OutputIdentity>);
+  ff_registry.Register("IdentityCycleDetector", new FFFactory<IdentityCycleDetector>);
   ff_registry.Register("InputIdentity", new FFFactory<InputIdentity>);
   ff_registry.Register("LexicalTranslationTrigger", new FFFactory<LexicalTranslationTrigger>);
   ff_registry.Register("WordPairFeatures", new FFFactory<WordPairFeatures>);
diff --git a/decoder/ff_wordalign.cc b/decoder/ff_wordalign.cc
index 338f1a72..ef3310b4 100644
--- a/decoder/ff_wordalign.cc
+++ b/decoder/ff_wordalign.cc
@@ -556,6 +556,68 @@ void BlunsomSynchronousParseHack::TraversalFeaturesImpl(const SentenceMetadata&
   SetStateMask(it->second, it->second + yield.size(), state);
 }
 
+IdentityCycleDetector::IdentityCycleDetector(const std::string& param) : FeatureFunction(2) {
+  length_min_ = 3;
+  if (!param.empty())
+    length_min_ = atoi(param.c_str());
+  assert(length_min_ >= 0);
+  ostringstream os;
+  os << "IdentityCycle_LenGT" << length_min_;
+  fid_ = FD::Convert(os.str());
+}
+
+inline bool IsIdentityTranslation(const void* state) {
+  return static_cast<const unsigned char*>(state)[0];
+}
+
+inline int SourceIndex(const void* state) {
+  unsigned char i = static_cast<const unsigned char*>(state)[1];
+  if (i == 255) return -1;
+  return i;
+}
+
+void IdentityCycleDetector::TraversalFeaturesImpl(const SentenceMetadata& smeta,
+                                     const Hypergraph::Edge& edge,
+                                     const std::vector<const void*>& ant_contexts,
+                                     SparseVector<double>* features,
+                                     SparseVector<double>* estimated_features,
+                                     void* context) const {
+  unsigned char* out_state = static_cast<unsigned char*>(context);
+  unsigned char& out_is_identity = out_state[0];
+  unsigned char& out_src_index = out_state[1];
+
+  if (edge.Arity() == 0) {
+    assert(edge.rule_->EWords() == 1);
+    assert(edge.rule_->FWords() == 1);
+    out_src_index = edge.i_;
+    out_is_identity = false;
+    if (edge.rule_->e_[0] == edge.rule_->f_[0]) {
+      const WordID word = edge.rule_->e_[0];
+      static map<WordID, bool> big_enough;
+      map<WordID,bool>::iterator it = big_enough_.find(word);
+      if (it == big_enough_.end()) {
+        out_is_identity = big_enough_[word] = strlen(TD::Convert(word)) >= length_min_;
+      } else {
+        out_is_identity = it->second;
+      }
+    }
+  } else if (edge.Arity() == 1) {
+    memcpy(context, ant_contexts[0], 2);
+  } else if (edge.Arity() == 2) {
+    bool left_identity = IsIdentityTranslation(ant_contexts[0]);
+    int left_index = SourceIndex(ant_contexts[0]);
+    bool right_identity = IsIdentityTranslation(ant_contexts[1]);
+    int right_index = SourceIndex(ant_contexts[1]);
+    if ((left_identity && left_index == right_index && !right_identity) ||
+        (right_identity && left_index == right_index && !left_identity)) {
+      features->set_value(fid_, 1.0);
+    }
+    out_is_identity = right_identity;
+    out_src_index = right_index;
+  } else { assert("really really bad"); }
+}
+
+
 InputIdentity::InputIdentity(const std::string& param) {}
 
 void InputIdentity::FireFeature(WordID src,
diff --git a/decoder/ff_wordalign.h b/decoder/ff_wordalign.h
index a1ffd9ca..8035000e 100644
--- a/decoder/ff_wordalign.h
+++ b/decoder/ff_wordalign.h
@@ -237,6 +237,23 @@ class WordPairFeatures : public FeatureFunction {
   std::vector<std::map<WordID, SparseVector<float> > > values_;  // fkeys_index -> e -> value
 };
 
+// fires when a len(word) >= length_min_ is translated as itself and then a self-transition is made
+class IdentityCycleDetector : public FeatureFunction {
+ public:
+  IdentityCycleDetector(const std::string& param);
+ protected:
+  virtual void TraversalFeaturesImpl(const SentenceMetadata& smeta,
+                                     const Hypergraph::Edge& edge,
+                                     const std::vector<const void*>& ant_contexts,
+                                     SparseVector<double>* features,
+                                     SparseVector<double>* estimated_features,
+                                     void* context) const;
+ private:
+  int length_min_;
+  int fid_;
+  mutable std::map<WordID, bool> big_enough_;
+};
+
 class InputIdentity : public FeatureFunction {
  public:
   InputIdentity(const std::string& param);