Updated OpenFST version to openfst-1.3.2-CL32004048 from Greco3.

Change-Id: I19b0db718256b35c0e3e5a7315f1ed6335e6dcac

16 files changed, 1585 insertions, 72 deletions

diff --git a/src/include/fst/extensions/far/compile-strings.h b/src/include/fst/extensions/far/compile-strings.h
index d7f4d6b..ca247db 100644
--- a/src/include/fst/extensions/far/compile-strings.h
+++ b/src/include/fst/extensions/far/compile-strings.h
@@ -56,7 +56,7 @@ class StringReader {
                const SymbolTable *syms = 0,
                Label unknown_label = kNoStateId)
       : nline_(0), strm_(istrm), source_(source), entry_type_(entry_type),
-        token_type_(token_type), done_(false),
+        token_type_(token_type), symbols_(syms), done_(false),
         compiler_(token_type, syms, unknown_label, allow_negative_labels) {
     Next();  // Initialize the reader to the first input.
   }
@@ -87,8 +87,12 @@ class StringReader {
       done_ = true;                  // whitespace at the end of a file.
   }
 
-  VectorFst<A> *GetVectorFst() {
+  VectorFst<A> *GetVectorFst(bool keep_symbols = false) {
     VectorFst<A> *fst = new VectorFst<A>;
+    if (keep_symbols) {
+      fst->SetInputSymbols(symbols_);
+      fst->SetOutputSymbols(symbols_);
+    }
     if (compiler_(content_, fst)) {
       return fst;
     } else {
@@ -97,9 +101,16 @@ class StringReader {
     }
   }
 
-  CompactFst<A, StringCompactor<A> > *GetCompactFst() {
-    CompactFst<A, StringCompactor<A> > *fst =
-        new CompactFst<A, StringCompactor<A> >;
+  CompactFst<A, StringCompactor<A> > *GetCompactFst(bool keep_symbols = false) {
+    CompactFst<A, StringCompactor<A> > *fst;
+    if (keep_symbols) {
+      VectorFst<A> tmp;
+      tmp.SetInputSymbols(symbols_);
+      tmp.SetOutputSymbols(symbols_);
+      fst = new CompactFst<A, StringCompactor<A> >(tmp);
+    } else {
+      fst = new CompactFst<A, StringCompactor<A> >;
+    }
     if (compiler_(content_, fst)) {
       return fst;
     } else {
@@ -114,6 +125,7 @@ class StringReader {
   string source_;
   EntryType entry_type_;
   TokenType token_type_;
+  const SymbolTable *symbols_;
   bool done_;
   StringCompiler<A> compiler_;
   string content_;  // The actual content of the input stream's next FST.
@@ -135,6 +147,8 @@ void FarCompileStrings(const vector<string> &in_fnames,
                        FarTokenType tt,
                        const string &symbols_fname,
                        const string &unknown_symbol,
+                       bool keep_symbols,
+                       bool initial_symbols,
                        bool allow_negative_labels,
                        bool file_list_input,
                        const string &key_prefix,
@@ -175,8 +189,9 @@ void FarCompileStrings(const vector<string> &in_fnames,
   const SymbolTable *syms = 0;
   typename Arc::Label unknown_label = kNoLabel;
   if (!symbols_fname.empty()) {
-    syms = SymbolTable::ReadText(symbols_fname,
-                                 allow_negative_labels);
+    SymbolTableTextOptions opts;
+    opts.allow_negative = allow_negative_labels;
+    syms = SymbolTable::ReadText(symbols_fname, opts);
     if (!syms) {
       FSTERROR() << "FarCompileStrings: error reading symbol table: "
                  << symbols_fname;
@@ -199,32 +214,47 @@ void FarCompileStrings(const vector<string> &in_fnames,
   vector<string> inputs;
   if (file_list_input) {
     for (int i = 1; i < in_fnames.size(); ++i) {
-      ifstream istrm(in_fnames[i].c_str());
+      istream *istrm = in_fnames.empty() ? &cin :
+          new ifstream(in_fnames[i].c_str());
       string str;
-      while (getline(istrm, str))
+      while (getline(*istrm, str))
         inputs.push_back(str);
+      if (!in_fnames.empty())
+        delete istrm;
     }
   } else {
     inputs = in_fnames;
   }
 
   for (int i = 0, n = 0; i < inputs.size(); ++i) {
+    if (generate_keys == 0 && inputs[i].empty()) {
+      FSTERROR() << "FarCompileStrings: read from a file instead of stdin or"
+                 << " set the --generate_keys flags.";
+      delete far_writer;
+      delete syms;
+      return;
+    }
     int key_size = generate_keys ? generate_keys :
         (entry_type == StringReader<Arc>::FILE ? 1 :
          KeySize(inputs[i].c_str()));
-    ifstream istrm(inputs[i].c_str());
+    istream *istrm = inputs[i].empty() ? &cin :
+        new ifstream(inputs[i].c_str());
 
+    bool keep_syms = keep_symbols;
     for (StringReader<Arc> reader(
-             istrm, inputs[i], entry_type, token_type,
-             allow_negative_labels, syms, unknown_label);
+             *istrm, inputs[i].empty() ? "stdin" : inputs[i],
+             entry_type, token_type, allow_negative_labels,
+             syms, unknown_label);
          !reader.Done();
          reader.Next()) {
       ++n;
       const Fst<Arc> *fst;
       if (compact)
-        fst = reader.GetCompactFst();
+        fst = reader.GetCompactFst(keep_syms);
       else
-        fst = reader.GetVectorFst();
+        fst = reader.GetVectorFst(keep_syms);
+      if (initial_symbols)
+        keep_syms = false;
       if (!fst) {
         FSTERROR() << "FarCompileStrings: compiling string number " << n
                    << " in file " << inputs[i] << " failed with token_type = "
@@ -236,6 +266,7 @@ void FarCompileStrings(const vector<string> &in_fnames,
                        (fet == FET_FILE ? "file" : "unknown"));
         delete far_writer;
         delete syms;
+        if (!inputs[i].empty()) delete istrm;
         return;
       }
       ostringstream keybuf;
@@ -260,6 +291,8 @@ void FarCompileStrings(const vector<string> &in_fnames,
     }
     if (generate_keys == 0)
       n = 0;
+    if (!inputs[i].empty())
+      delete istrm;
   }
 
   delete far_writer;
diff --git a/src/include/fst/extensions/far/equal.h b/src/include/fst/extensions/far/equal.h
new file mode 100644
index 0000000..be82e2d
--- /dev/null
+++ b/src/include/fst/extensions/far/equal.h
@@ -0,0 +1,99 @@
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: allauzen@google.com (Cyril Allauzen)
+
+#ifndef FST_EXTENSIONS_FAR_EQUAL_H_
+#define FST_EXTENSIONS_FAR_EQUAL_H_
+
+#include <string>
+
+#include <fst/extensions/far/far.h>
+#include <fst/equal.h>
+
+namespace fst {
+
+template <class Arc>
+bool FarEqual(const string &filename1,
+             const string &filename2,
+             float delta = kDelta,
+             const string &begin_key = string(),
+             const string &end_key = string()) {
+
+  FarReader<Arc> *reader1 = FarReader<Arc>::Open(filename1);
+  FarReader<Arc> *reader2 = FarReader<Arc>::Open(filename2);
+  if (!reader1 || !reader2) {
+    delete reader1;
+    delete reader2;
+    VLOG(1) << "FarEqual: cannot open input Far file(s)";
+    return false;
+  }
+
+  if (!begin_key.empty()) {
+    bool find_begin1 = reader1->Find(begin_key);
+    bool find_begin2 = reader2->Find(begin_key);
+    if (!find_begin1 || !find_begin2) {
+      bool ret = !find_begin1 && !find_begin2;
+      if (!ret) {
+        VLOG(1) << "FarEqual: key \"" << begin_key << "\" missing from "
+                << (find_begin1 ? "second" : "first") << " archive.";
+      }
+      delete reader1;
+      delete reader2;
+      return ret;
+    }
+  }
+
+  for(; !reader1->Done() && !reader2->Done();
+      reader1->Next(), reader2->Next()) {
+    const string key1 = reader1->GetKey();
+    const string key2 = reader2->GetKey();
+    if (!end_key.empty() && end_key < key1 && end_key < key2) {
+      delete reader1;
+      delete reader2;
+      return true;
+    }
+    if (key1 != key2) {
+      VLOG(1) << "FarEqual: mismatched keys \""
+              << key1 << "\" <> \"" << key2 << "\".";
+      delete reader1;
+      delete reader2;
+      return false;
+    }
+    if (!Equal(reader1->GetFst(), reader2->GetFst(), delta)) {
+      VLOG(1) << "FarEqual: Fsts for key \"" << key1 << "\" are not equal.";
+      delete reader1;
+      delete reader2;
+      return false;
+    }
+  }
+
+  if (!reader1->Done() || !reader2->Done()) {
+    VLOG(1) << "FarEqual: key \""
+            << (reader1->Done() ? reader2->GetKey() : reader1->GetKey())
+            << "\" missing form " << (reader2->Done() ? "first" : "second")
+            << " archive.";
+    delete reader1;
+    delete reader2;
+    return false;
+  }
+
+  delete reader1;
+  delete reader2;
+  return true;
+}
+
+}  // namespace fst
+
+#endif  // FST_EXTENSIONS_FAR_EQUAL_H_
diff --git a/src/include/fst/extensions/far/extract.h b/src/include/fst/extensions/far/extract.h
index 022ca60..d6f92ff 100644
--- a/src/include/fst/extensions/far/extract.h
+++ b/src/include/fst/extensions/far/extract.h
@@ -70,7 +70,7 @@ void FarExtract(const vector<string> &ifilenames,
       if (nrep > 0) {
         ostringstream tmp;
         tmp << '.' << nrep;
-        key += tmp.str();
+        key.append(tmp.str().data(), tmp.str().size());
       }
       ofilename = key;
     }
diff --git a/src/include/fst/extensions/far/far.h b/src/include/fst/extensions/far/far.h
index 82b9e5c..acce76e 100644
--- a/src/include/fst/extensions/far/far.h
+++ b/src/include/fst/extensions/far/far.h
@@ -32,6 +32,13 @@ namespace fst {
 enum FarEntryType { FET_LINE, FET_FILE };
 enum FarTokenType { FTT_SYMBOL, FTT_BYTE, FTT_UTF8 };
 
+inline bool IsFst(const string &filename) {
+  ifstream strm(filename.c_str());
+  if (!strm)
+    return false;
+  return IsFstHeader(strm, filename);
+}
+
 // FST archive header class
 class FarHeader {
  public:
@@ -40,8 +47,11 @@ class FarHeader {
 
   bool Read(const string &filename) {
     FstHeader fsthdr;
-    if (filename.empty()) {  // Header reading unsupported on stdin.
-      return false;
+    if (filename.empty()) {
+      // Header reading unsupported on stdin. Assumes STList and StdArc.
+      fartype_ = "stlist";
+      arctype_ = "standard";
+      return true;
     } else if (IsSTTable(filename)) {  // Check if STTable
       ReadSTTableHeader(filename, &fsthdr);
       fartype_ = "sttable";
@@ -52,6 +62,12 @@ class FarHeader {
       fartype_ = "sttable";
       arctype_ = fsthdr.ArcType().empty() ? "unknown" : fsthdr.ArcType();
       return true;
+    } else if (IsFst(filename)) {  // Check if Fst
+      ifstream istrm(filename.c_str());
+      fsthdr.Read(istrm, filename);
+      fartype_ = "fst";
+      arctype_ = fsthdr.ArcType().empty() ? "unknown" : fsthdr.ArcType();
+      return true;
     }
     return false;
   }
@@ -61,8 +77,12 @@ class FarHeader {
   string arctype_;
 };
 
-enum FarType { FAR_DEFAULT = 0, FAR_STTABLE = 1, FAR_STLIST = 2,
-               FAR_SSTABLE = 3 };
+enum FarType {
+  FAR_DEFAULT = 0,
+  FAR_STTABLE = 1,
+  FAR_STLIST = 2,
+  FAR_FST = 3,
+};
 
 // This class creates an archive of FSTs.
 template <class A>
@@ -153,7 +173,7 @@ class STTableFarWriter : public FarWriter<A> {
  public:
   typedef A Arc;
 
-  static STTableFarWriter *Create(const string filename) {
+  static STTableFarWriter *Create(const string &filename) {
     STTableWriter<Fst<A>, FstWriter<A> > *writer =
         STTableWriter<Fst<A>, FstWriter<A> >::Create(filename);
     return new STTableFarWriter(writer);
@@ -183,7 +203,7 @@ class STListFarWriter : public FarWriter<A> {
  public:
   typedef A Arc;
 
-  static STListFarWriter *Create(const string filename) {
+  static STListFarWriter *Create(const string &filename) {
     STListWriter<Fst<A>, FstWriter<A> > *writer =
         STListWriter<Fst<A>, FstWriter<A> >::Create(filename);
     return new STListFarWriter(writer);
@@ -209,6 +229,43 @@ class STListFarWriter : public FarWriter<A> {
 
 
 template <class A>
+class FstFarWriter : public FarWriter<A> {
+ public:
+  typedef A Arc;
+
+  explicit FstFarWriter(const string &filename)
+      : filename_(filename), error_(false), written_(false) {}
+
+  static FstFarWriter *Create(const string &filename) {
+    return new FstFarWriter(filename);
+  }
+
+  void Add(const string &key, const Fst<A> &fst) {
+    if (written_) {
+      LOG(WARNING) << "FstFarWriter::Add: only one Fst supported,"
+                 << " subsequent entries discarded.";
+    } else {
+      error_ = !fst.Write(filename_);
+      written_ = true;
+    }
+  }
+
+  FarType Type() const { return FAR_FST; }
+
+  bool Error() const { return error_; }
+
+  ~FstFarWriter() {}
+
+ private:
+  string filename_;
+  bool error_;
+  bool written_;
+
+  DISALLOW_COPY_AND_ASSIGN(FstFarWriter);
+};
+
+
+template <class A>
 FarWriter<A> *FarWriter<A>::Create(const string &filename, FarType type) {
   switch(type) {
     case FAR_DEFAULT:
@@ -220,6 +277,9 @@ FarWriter<A> *FarWriter<A>::Create(const string &filename, FarType type) {
     case FAR_STLIST:
       return STListFarWriter<A>::Create(filename);
       break;
+    case FAR_FST:
+      return FstFarWriter<A>::Create(filename);
+      break;
     default:
       LOG(ERROR) << "FarWriter::Create: unknown far type";
       return 0;
@@ -331,6 +391,114 @@ class STListFarReader : public FarReader<A> {
   DISALLOW_COPY_AND_ASSIGN(STListFarReader);
 };
 
+template <class A>
+class FstFarReader : public FarReader<A> {
+ public:
+  typedef A Arc;
+
+  static FstFarReader *Open(const string &filename) {
+    vector<string> filenames;
+    filenames.push_back(filename);
+    return new FstFarReader<A>(filenames);
+  }
+
+  static FstFarReader *Open(const vector<string> &filenames) {
+    return new FstFarReader<A>(filenames);
+  }
+
+  FstFarReader(const vector<string> &filenames)
+      : keys_(filenames), has_stdin_(false), pos_(0), fst_(0), error_(false) {
+    sort(keys_.begin(), keys_.end());
+    streams_.resize(keys_.size(), 0);
+    for (size_t i = 0; i < keys_.size(); ++i) {
+      if (keys_[i].empty()) {
+        if (!has_stdin_) {
+          streams_[i] = &cin;
+          //sources_[i] = "stdin";
+          has_stdin_ = true;
+        } else {
+          FSTERROR() << "FstFarReader::FstFarReader: stdin should only "
+                     << "appear once in the input file list.";
+          error_ = true;
+          return;
+        }
+      } else {
+        streams_[i] = new ifstream(
+            keys_[i].c_str(), ifstream::in | ifstream::binary);
+      }
+    }
+    if (pos_ >= keys_.size()) return;
+    ReadFst();
+  }
+
+  void Reset() {
+    if (has_stdin_) {
+      FSTERROR() << "FstFarReader::Reset: operation not supported on stdin";
+      error_ = true;
+      return;
+    }
+    pos_ = 0;
+    ReadFst();
+  }
+
+  bool Find(const string &key) {
+    if (has_stdin_) {
+      FSTERROR() << "FstFarReader::Find: operation not supported on stdin";
+      error_ = true;
+      return false;
+    }
+    pos_ = 0;//TODO
+    ReadFst();
+    return true;
+  }
+
+  bool Done() const { return error_ || pos_ >= keys_.size(); }
+
+  void Next() {
+    ++pos_;
+    ReadFst();
+  }
+
+  const string &GetKey() const {
+    return keys_[pos_];
+  }
+
+  const Fst<A> &GetFst() const {
+    return *fst_;
+  }
+
+  FarType Type() const { return FAR_FST; }
+
+  bool Error() const { return error_; }
+
+  ~FstFarReader() {
+    if (fst_) delete fst_;
+    for (size_t i = 0; i < keys_.size(); ++i)
+      delete streams_[i];
+  }
+
+ private:
+  void ReadFst() {
+    if (fst_) delete fst_;
+    if (pos_ >= keys_.size()) return;
+    streams_[pos_]->seekg(0);
+    fst_ = Fst<A>::Read(*streams_[pos_], FstReadOptions());
+    if (!fst_) {
+      FSTERROR() << "FstFarReader: error reading Fst from: " << keys_[pos_];
+      error_ = true;
+    }
+  }
+
+ private:
+  vector<string> keys_;
+  vector<istream*> streams_;
+  bool has_stdin_;
+  size_t pos_;
+  mutable Fst<A> *fst_;
+  mutable bool error_;
+
+  DISALLOW_COPY_AND_ASSIGN(FstFarReader);
+};
 
 template <class A>
 FarReader<A> *FarReader<A>::Open(const string &filename) {
@@ -340,6 +508,8 @@ FarReader<A> *FarReader<A>::Open(const string &filename) {
     return STTableFarReader<A>::Open(filename);
   else if (IsSTList(filename))
     return STListFarReader<A>::Open(filename);
+  else if (IsFst(filename))
+    return FstFarReader<A>::Open(filename);
   return 0;
 }
 
@@ -352,6 +522,8 @@ FarReader<A> *FarReader<A>::Open(const vector<string> &filenames) {
     return STTableFarReader<A>::Open(filenames);
   else if (!filenames.empty() && IsSTList(filenames[0]))
     return STListFarReader<A>::Open(filenames);
+  else if (!filenames.empty() && IsFst(filenames[0]))
+    return FstFarReader<A>::Open(filenames);
   return 0;
 }
 
diff --git a/src/include/fst/extensions/far/farscript.h b/src/include/fst/extensions/far/farscript.h
index 9c3b1ca..3a9c145 100644
--- a/src/include/fst/extensions/far/farscript.h
+++ b/src/include/fst/extensions/far/farscript.h
@@ -27,6 +27,7 @@ using std::vector;
 #include <fst/script/arg-packs.h>
 #include <fst/extensions/far/compile-strings.h>
 #include <fst/extensions/far/create.h>
+#include <fst/extensions/far/equal.h>
 #include <fst/extensions/far/extract.h>
 #include <fst/extensions/far/info.h>
 #include <fst/extensions/far/print-strings.h>
@@ -51,6 +52,8 @@ struct FarCompileStringsArgs {
   const FarTokenType tt;
   const string &symbols_fname;
   const string &unknown_symbol;
+  const bool keep_symbols;
+  const bool initial_symbols;
   const bool allow_negative_labels;
   const bool file_list_input;
   const string &key_prefix;
@@ -65,6 +68,8 @@ struct FarCompileStringsArgs {
                         FarTokenType tt,
                         const string &symbols_fname,
                         const string &unknown_symbol,
+                        bool keep_symbols,
+                        bool initial_symbols,
                         bool allow_negative_labels,
                         bool file_list_input,
                         const string &key_prefix,
@@ -72,6 +77,7 @@ struct FarCompileStringsArgs {
       in_fnames(in_fnames), out_fname(out_fname), fst_type(fst_type),
       far_type(far_type), generate_keys(generate_keys), fet(fet),
       tt(tt), symbols_fname(symbols_fname), unknown_symbol(unknown_symbol),
+      keep_symbols(keep_symbols), initial_symbols(initial_symbols),
       allow_negative_labels(allow_negative_labels),
       file_list_input(file_list_input), key_prefix(key_prefix),
       key_suffix(key_suffix) { }
@@ -82,7 +88,8 @@ void FarCompileStrings(FarCompileStringsArgs *args) {
   fst::FarCompileStrings<Arc>(
       args->in_fnames, args->out_fname, args->fst_type, args->far_type,
       args->generate_keys, args->fet, args->tt, args->symbols_fname,
-      args->unknown_symbol, args->allow_negative_labels, args->file_list_input,
+      args->unknown_symbol, args->keep_symbols, args->initial_symbols,
+      args->allow_negative_labels, args->file_list_input,
       args->key_prefix, args->key_suffix);
 }
 
@@ -97,6 +104,8 @@ void FarCompileStrings(
     FarTokenType tt,
     const string &symbols_fname,
     const string &unknown_symbol,
+    bool keep_symbols,
+    bool initial_symbols,
     bool allow_negative_labels,
     bool file_list_input,
     const string &key_prefix,
@@ -143,6 +152,25 @@ void FarCreate(const vector<string> &in_fnames,
                const string &key_suffix);
 
 
+typedef args::Package<const string &, const string &, float,
+                      const string &, const string &> FarEqualInnerArgs;
+typedef args::WithReturnValue<bool, FarEqualInnerArgs> FarEqualArgs;
+
+template <class Arc>
+void FarEqual(FarEqualArgs *args) {
+  args->retval = fst::FarEqual<Arc>(
+      args->args.arg1, args->args.arg2, args->args.arg3,
+      args->args.arg4, args->args.arg5);
+}
+
+bool FarEqual(const string &filename1,
+              const string &filename2,
+              const string &arc_type,
+              float delta = kDelta,
+              const string &begin_key = string(),
+              const string &end_key = string());
+
+
 typedef args::Package<const vector<string> &, int32,
                       const string&, const string&, const string&,
                       const string&> FarExtractArgs;
@@ -180,7 +208,9 @@ struct FarPrintStringsArgs {
   const string &begin_key;
   const string &end_key;
   const bool print_key;
+  const bool print_weight;
   const string &symbols_fname;
+  const bool initial_symbols;
   const int32 generate_filenames;
   const string &filename_prefix;
   const string &filename_suffix;
@@ -188,12 +218,14 @@ struct FarPrintStringsArgs {
   FarPrintStringsArgs(
       const vector<string> &ifilenames, const FarEntryType entry_type,
       const FarTokenType token_type, const string &begin_key,
-      const string &end_key,  const bool print_key,
-      const string &symbols_fname, const int32 generate_filenames,
+      const string &end_key,  const bool print_key, const bool print_weight,
+      const string &symbols_fname, const bool initial_symbols,
+      const int32 generate_filenames,
       const string &filename_prefix, const string &filename_suffix) :
       ifilenames(ifilenames), entry_type(entry_type), token_type(token_type),
-      begin_key(begin_key), end_key(end_key), print_key(print_key),
-      symbols_fname(symbols_fname),
+      begin_key(begin_key), end_key(end_key),
+      print_key(print_key), print_weight(print_weight),
+      symbols_fname(symbols_fname), initial_symbols(initial_symbols),
       generate_filenames(generate_filenames), filename_prefix(filename_prefix),
       filename_suffix(filename_suffix) { }
 };
@@ -202,9 +234,9 @@ template <class Arc>
 void FarPrintStrings(FarPrintStringsArgs *args) {
   fst::FarPrintStrings<Arc>(
       args->ifilenames, args->entry_type, args->token_type,
-      args->begin_key, args->end_key, args->print_key,
-      args->symbols_fname, args->generate_filenames, args->filename_prefix,
-      args->filename_suffix);
+      args->begin_key, args->end_key, args->print_key, args->print_weight,
+      args->symbols_fname, args->initial_symbols, args->generate_filenames,
+      args->filename_prefix, args->filename_suffix);
 }
 
 
@@ -215,7 +247,9 @@ void FarPrintStrings(const vector<string> &ifilenames,
                      const string &begin_key,
                      const string &end_key,
                      const bool print_key,
+                     const bool print_weight,
                      const string &symbols_fname,
+                     const bool initial_symbols,
                      const int32 generate_filenames,
                      const string &filename_prefix,
                      const string &filename_suffix);
@@ -227,6 +261,7 @@ void FarPrintStrings(const vector<string> &ifilenames,
 #define REGISTER_FST_FAR_OPERATIONS(ArcType)                            \
   REGISTER_FST_OPERATION(FarCompileStrings, ArcType, FarCompileStringsArgs); \
   REGISTER_FST_OPERATION(FarCreate, ArcType, FarCreateArgs);            \
+  REGISTER_FST_OPERATION(FarEqual, ArcType, FarEqualArgs);              \
   REGISTER_FST_OPERATION(FarExtract, ArcType, FarExtractArgs);          \
   REGISTER_FST_OPERATION(FarInfo, ArcType, FarInfoArgs);                \
   REGISTER_FST_OPERATION(FarPrintStrings, ArcType, FarPrintStringsArgs)
diff --git a/src/include/fst/extensions/far/info.h b/src/include/fst/extensions/far/info.h
index f010546..100fe68 100644
--- a/src/include/fst/extensions/far/info.h
+++ b/src/include/fst/extensions/far/info.h
@@ -34,7 +34,7 @@ void CountStatesAndArcs(const Fst<Arc> &fst, size_t *nstate, size_t *narc) {
   StateIterator<Fst<Arc> > siter(fst);
   for (; !siter.Done(); siter.Next(), ++(*nstate)) {
     ArcIterator<Fst<Arc> > aiter(fst, siter.Value());
-    for (; !aiter.Done(); aiter.Next(), ++(*narc));
+    for (; !aiter.Done(); aiter.Next(), ++(*narc)) {}
   }
 }
 
diff --git a/src/include/fst/extensions/far/print-strings.h b/src/include/fst/extensions/far/print-strings.h
index aff1e51..dcc7351 100644
--- a/src/include/fst/extensions/far/print-strings.h
+++ b/src/include/fst/extensions/far/print-strings.h
@@ -27,17 +27,21 @@
 using std::vector;
 
 #include <fst/extensions/far/far.h>
+#include <fst/shortest-distance.h>
 #include <fst/string.h>
 
+DECLARE_string(far_field_separator);
+
 namespace fst {
 
 template <class Arc>
 void FarPrintStrings(
     const vector<string> &ifilenames, const FarEntryType entry_type,
     const FarTokenType far_token_type, const string &begin_key,
-    const string &end_key, const bool print_key, const string &symbols_fname,
-    const int32 generate_filenames, const string &filename_prefix,
-    const string &filename_suffix) {
+    const string &end_key, const bool print_key, const bool print_weight,
+    const string &symbols_fname, const bool initial_symbols,
+    const int32 generate_filenames,
+    const string &filename_prefix, const string &filename_suffix) {
 
   typename StringPrinter<Arc>::TokenType token_type;
   if (far_token_type == FTT_SYMBOL) {
@@ -54,7 +58,9 @@ void FarPrintStrings(
   const SymbolTable *syms = 0;
   if (!symbols_fname.empty()) {
     // allow negative flag?
-    syms = SymbolTable::ReadText(symbols_fname, true);
+    SymbolTableTextOptions opts;
+    opts.allow_negative = true;
+    syms = SymbolTable::ReadText(symbols_fname, opts);
     if (!syms) {
       FSTERROR() << "FarPrintStrings: error reading symbol table: "
                  << symbols_fname;
@@ -62,8 +68,6 @@ void FarPrintStrings(
     }
   }
 
-  StringPrinter<Arc> string_printer(token_type, syms);
-
   FarReader<Arc> *far_reader = FarReader<Arc>::Open(ifilenames);
   if (!far_reader) return;
 
@@ -83,14 +87,21 @@ void FarPrintStrings(
     okey = key;
 
     const Fst<Arc> &fst = far_reader->GetFst();
+    if (i == 1 && initial_symbols && syms == 0 && fst.InputSymbols() != 0)
+      syms = fst.InputSymbols()->Copy();
     string str;
     VLOG(2) << "Handling key: " << key;
+    StringPrinter<Arc> string_printer(
+        token_type, syms ? syms : fst.InputSymbols());
     string_printer(fst, &str);
 
     if (entry_type == FET_LINE) {
       if (print_key)
-        cout << key << "\t";
-      cout << str << endl;
+        cout << key << FLAGS_far_field_separator[0];
+      cout << str;
+      if (print_weight)
+        cout << FLAGS_far_field_separator[0] << ShortestDistance(fst);
+      cout << endl;
     } else if (entry_type == FET_FILE) {
       stringstream sstrm;
       if (generate_filenames) {
@@ -117,6 +128,7 @@ void FarPrintStrings(
         ostrm << "\n";
     }
   }
+  delete syms;
 }
 
 
diff --git a/src/include/fst/extensions/far/stlist.h b/src/include/fst/extensions/far/stlist.h
index 4738181..1cdc80c 100644
--- a/src/include/fst/extensions/far/stlist.h
+++ b/src/include/fst/extensions/far/stlist.h
@@ -26,6 +26,7 @@
 
 #include <iostream>
 #include <fstream>
+#include <sstream>
 #include <fst/util.h>
 
 #include <algorithm>
@@ -58,7 +59,7 @@ class STListWriter {
 
   explicit STListWriter(const string filename)
       : stream_(
-          filename.empty() ? &std::cout :
+          filename.empty() ? &cout :
           new ofstream(filename.c_str(), ofstream::out | ofstream::binary)),
         error_(false) {
     WriteType(*stream_, kSTListMagicNumber);
@@ -92,7 +93,7 @@ class STListWriter {
 
   ~STListWriter() {
     WriteType(*stream_, string());
-    if (stream_ != &std::cout)
+    if (stream_ != &cout)
       delete stream_;
   }
 
@@ -127,7 +128,7 @@ class STListReader {
     for (size_t i = 0; i < filenames.size(); ++i) {
       if (filenames[i].empty()) {
         if (!has_stdin) {
-          streams_[i] = &std::cin;
+          streams_[i] = &cin;
           sources_[i] = "stdin";
           has_stdin = true;
         } else {
@@ -177,7 +178,7 @@ class STListReader {
 
   ~STListReader() {
     for (size_t i = 0; i < streams_.size(); ++i) {
-      if (streams_[i] != &std::cin)
+      if (streams_[i] != &cin)
         delete streams_[i];
     }
     if (entry_)
diff --git a/src/include/fst/extensions/far/sttable.h b/src/include/fst/extensions/far/sttable.h
index 3a03133..3ce0a4b 100644
--- a/src/include/fst/extensions/far/sttable.h
+++ b/src/include/fst/extensions/far/sttable.h
@@ -29,6 +29,7 @@
 #include <algorithm>
 #include <iostream>
 #include <fstream>
+#include <sstream>
 #include <fst/util.h>
 
 namespace fst {
diff --git a/src/include/fst/extensions/ngram/bitmap-index.h b/src/include/fst/extensions/ngram/bitmap-index.h
new file mode 100644
index 0000000..f5a5ba7
--- /dev/null
+++ b/src/include/fst/extensions/ngram/bitmap-index.h
@@ -0,0 +1,183 @@
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: sorenj@google.com (Jeffrey Sorensen)
+
+#ifndef FST_EXTENSIONS_NGRAM_BITMAP_INDEX_H_
+#define FST_EXTENSIONS_NGRAM_BITMAP_INDEX_H_
+
+#include <vector>
+using std::vector;
+
+#include <fst/compat.h>
+
+// This class is a bitstring storage class with an index that allows
+// seeking to the Nth set or clear bit in time O(Log(N)) where N is
+// the length of the bit vector.  In addition, it allows counting set or
+// clear bits over ranges in constant time.
+//
+// This is accomplished by maintaining an "secondary" index of limited
+// size in bits that maintains a running count of the number of bits set
+// in each block of bitmap data.  A block is defined as the number of
+// uint64 values that can fit in the secondary index before an overflow
+// occurs.
+//
+// To handle overflows, a "primary" index containing a running count of
+// bits set in each block is created using the type uint64.
+
+namespace fst {
+
+class BitmapIndex {
+ public:
+  static size_t StorageSize(size_t size) {
+    return ((size + kStorageBlockMask) >> kStorageLogBitSize);
+  }
+
+  BitmapIndex() : bits_(NULL), size_(0) { }
+
+  bool Get(size_t index) const {
+    return (bits_[index >> kStorageLogBitSize] &
+            (kOne << (index & kStorageBlockMask))) != 0;
+  }
+
+  static void Set(uint64* bits, size_t index) {
+    bits[index >> kStorageLogBitSize] |= (kOne << (index & kStorageBlockMask));
+  }
+
+  static void Clear(uint64* bits, size_t index) {
+    bits[index >> kStorageLogBitSize] &= ~(kOne << (index & kStorageBlockMask));
+  }
+
+  size_t Bits() const {
+    return size_;
+  }
+
+  size_t ArraySize() const {
+    return StorageSize(size_);
+  }
+
+  // Returns the number of one bits in the bitmap
+  size_t GetOnesCount() const {
+    return primary_index_[primary_index_size() - 1];
+  }
+
+  // Returns the number of one bits in positions 0 to limit - 1.
+  // REQUIRES: limit <= Bits()
+  size_t Rank1(size_t end) const;
+
+  // Returns the number of one bits in the range start to end - 1.
+  // REQUIRES: limit <= Bits()
+  size_t GetOnesCountInRange(size_t start, size_t end) const {
+    return Rank1(end) - Rank1(start);
+  }
+
+  // Returns the number of zero bits in positions 0 to limit - 1.
+  // REQUIRES: limit <= Bits()
+  size_t Rank0(size_t end) const {
+    return end - Rank1(end);
+  }
+
+  // Returns the number of zero bits in the range start to end - 1.
+  // REQUIRES: limit <= Bits()
+  size_t GetZeroesCountInRange(size_t start, size_t end) const {
+    return end - start - GetOnesCountInRange(start, end);
+  }
+
+  // Return true if any bit between begin inclusive and end exclusive
+  // is set.  0 <= begin <= end <= Bits() is required.
+  //
+  bool TestRange(size_t start, size_t end) const {
+    return Rank1(end) > Rank1(start);
+  }
+
+  // Returns the offset to the nth set bit (zero based)
+  // or Bits() if index >= number of ones
+  size_t Select1(size_t bit_index) const;
+
+  // Returns the offset to the nth clear bit (zero based)
+  // or Bits() if index > number of
+  size_t Select0(size_t bit_index) const;
+
+  // Rebuilds from index for the associated Bitmap, should be called
+  // whenever changes have been made to the Bitmap or else behavior
+  // of the indexed bitmap methods will be undefined.
+  void BuildIndex(const uint64 *bits, size_t size);
+
+  // the secondary index accumulates counts until it can possibly overflow
+  // this constant computes the number of uint64 units that can fit into
+  // units the size of uint16.
+  static const uint64 kOne = 1;
+  static const uint32 kStorageBitSize = 64;
+  static const uint32 kStorageLogBitSize = 6;
+  static const uint32 kSecondaryBlockSize = ((1 << 16) - 1)
+      >> kStorageLogBitSize;
+
+ private:
+  static const uint32 kStorageBlockMask = kStorageBitSize - 1;
+
+  // returns, from the index, the count of ones up to array_index
+  size_t get_index_ones_count(size_t array_index) const;
+
+  // because the indexes, both primary and secondary, contain a running
+  // count of the population of one bits contained in [0,i), there is
+  // no reason to have an element in the zeroth position as this value would
+  // necessarily be zero.  (The bits are indexed in a zero based way.)  Thus
+  // we don't store the 0th element in either index.  Both of the following
+  // functions, if greater than 0, must be decremented by one before retreiving
+  // the value from the corresponding array.
+  // returns the 1 + the block that contains the bitindex in question
+  // the inverted version works the same but looks for zeros using an inverted
+  // view of the index
+  size_t find_primary_block(size_t bit_index) const;
+
+  size_t find_inverted_primary_block(size_t bit_index) const;
+
+  // similarly, the secondary index (which resets its count to zero at
+  // the end of every kSecondaryBlockSize entries) does not store the element
+  // at 0.  Note that the rem_bit_index parameter is the number of bits
+  // within the secondary block, after the bits accounted for by the primary
+  // block have been removed (i.e. the remaining bits)  And, because we
+  // reset to zero with each new block, there is no need to store those
+  // actual zeros.
+  // returns 1 + the secondary block that contains the bitindex in question
+  size_t find_secondary_block(size_t block, size_t rem_bit_index) const;
+
+  size_t find_inverted_secondary_block(size_t block, size_t rem_bit_index)
+      const;
+
+  // We create a primary index based upon the number of secondary index
+  // blocks.  The primary index uses fields wide enough to accomodate any
+  // index of the bitarray so cannot overflow
+  // The primary index is the actual running
+  // count of one bits set for all blocks (and, thus, all uint64s).
+  size_t primary_index_size() const {
+    return (ArraySize() + kSecondaryBlockSize - 1) / kSecondaryBlockSize;
+  }
+
+  const uint64* bits_;
+  size_t size_;
+
+  // The primary index contains the running popcount of all blocks
+  // which means the nth value contains the popcounts of
+  // [0,n*kSecondaryBlockSize], however, the 0th element is omitted.
+  vector<uint32> primary_index_;
+  // The secondary index contains the running popcount of the associated
+  // bitmap.  It is the same length (in units of uint16) as the
+  // bitmap's map is in units of uint64s.
+  vector<uint16> secondary_index_;
+};
+
+}  // end namespace fst
+
+#endif  // FST_EXTENSIONS_NGRAM_BITMAP_INDEX_H_
diff --git a/src/include/fst/extensions/ngram/ngram-fst.h b/src/include/fst/extensions/ngram/ngram-fst.h
new file mode 100644
index 0000000..eee664a
--- /dev/null
+++ b/src/include/fst/extensions/ngram/ngram-fst.h
@@ -0,0 +1,912 @@
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: sorenj@google.com (Jeffrey Sorensen)
+//
+#ifndef FST_EXTENSIONS_NGRAM_NGRAM_FST_H_
+#define FST_EXTENSIONS_NGRAM_NGRAM_FST_H_
+
+#include <stddef.h>
+#include <string.h>
+#include <algorithm>
+#include <string>
+#include <vector>
+using std::vector;
+
+#include <fst/compat.h>
+#include <fst/fstlib.h>
+#include <fst/extensions/ngram/bitmap-index.h>
+
+// NgramFst implements a n-gram language model based upon the LOUDS data
+// structure.  Please refer to "Unary Data Strucutres for Language Models"
+// http://research.google.com/pubs/archive/37218.pdf
+
+namespace fst {
+template <class A> class NGramFst;
+template <class A> class NGramFstMatcher;
+
+// Instance data containing mutable state for bookkeeping repeated access to
+// the same state.
+template <class A>
+struct NGramFstInst {
+  typedef typename A::Label Label;
+  typedef typename A::StateId StateId;
+  typedef typename A::Weight Weight;
+  StateId state_;
+  size_t num_futures_;
+  size_t offset_;
+  size_t node_;
+  StateId node_state_;
+  vector<Label> context_;
+  StateId context_state_;
+  NGramFstInst()
+      : state_(kNoStateId), node_state_(kNoStateId),
+        context_state_(kNoStateId) { }
+};
+
+// Implementation class for LOUDS based NgramFst interface
+template <class A>
+class NGramFstImpl : public FstImpl<A> {
+  using FstImpl<A>::SetInputSymbols;
+  using FstImpl<A>::SetOutputSymbols;
+  using FstImpl<A>::SetType;
+  using FstImpl<A>::WriteHeader;
+
+  friend class ArcIterator<NGramFst<A> >;
+  friend class NGramFstMatcher<A>;
+
+ public:
+  using FstImpl<A>::InputSymbols;
+  using FstImpl<A>::SetProperties;
+  using FstImpl<A>::Properties;
+
+  typedef A Arc;
+  typedef typename A::Label Label;
+  typedef typename A::StateId StateId;
+  typedef typename A::Weight Weight;
+
+  NGramFstImpl() : data_(0), owned_(false) {
+    SetType("ngram");
+    SetInputSymbols(NULL);
+    SetOutputSymbols(NULL);
+    SetProperties(kStaticProperties);
+  }
+
+  NGramFstImpl(const Fst<A> &fst, vector<StateId>* order_out);
+
+  ~NGramFstImpl() {
+    if (owned_) {
+      delete [] data_;
+    }
+  }
+
+  static NGramFstImpl<A>* Read(istream &strm,  // NOLINT
+                               const FstReadOptions &opts) {
+    NGramFstImpl<A>* impl = new NGramFstImpl();
+    FstHeader hdr;
+    if (!impl->ReadHeader(strm, opts, kMinFileVersion, &hdr)) return 0;
+    uint64 num_states, num_futures, num_final;
+    const size_t offset = sizeof(num_states) + sizeof(num_futures) +
+        sizeof(num_final);
+    // Peek at num_states and num_futures to see how much more needs to be read.
+    strm.read(reinterpret_cast<char *>(&num_states), sizeof(num_states));
+    strm.read(reinterpret_cast<char *>(&num_futures), sizeof(num_futures));
+    strm.read(reinterpret_cast<char *>(&num_final), sizeof(num_final));
+    size_t size = Storage(num_states, num_futures, num_final);
+    char* data = new char[size];
+    // Copy num_states, num_futures and num_final back into data.
+    memcpy(data, reinterpret_cast<char *>(&num_states), sizeof(num_states));
+    memcpy(data + sizeof(num_states), reinterpret_cast<char *>(&num_futures),
+           sizeof(num_futures));
+    memcpy(data + sizeof(num_states) + sizeof(num_futures),
+           reinterpret_cast<char *>(&num_final), sizeof(num_final));
+    strm.read(data + offset, size - offset);
+    if (!strm) {
+      delete impl;
+      return NULL;
+    }
+    impl->Init(data, true /* owned */);
+    return impl;
+  }
+
+  bool Write(ostream &strm,   // NOLINT
+             const FstWriteOptions &opts) const {
+    FstHeader hdr;
+    hdr.SetStart(Start());
+    hdr.SetNumStates(num_states_);
+    WriteHeader(strm, opts, kFileVersion, &hdr);
+    strm.write(data_, Storage(num_states_, num_futures_, num_final_));
+    return strm;
+  }
+
+  StateId Start() const {
+    return 1;
+  }
+
+  Weight Final(StateId state) const {
+    if (final_index_.Get(state)) {
+      return final_probs_[final_index_.Rank1(state)];
+    } else {
+      return Weight::Zero();
+    }
+  }
+
+  size_t NumArcs(StateId state, NGramFstInst<A> *inst = NULL) const {
+    if (inst == NULL) {
+      const size_t next_zero = future_index_.Select0(state + 1);
+      const size_t this_zero = future_index_.Select0(state);
+      return next_zero - this_zero - 1;
+    }
+    SetInstFuture(state, inst);
+    return inst->num_futures_ + ((state == 0) ? 0 : 1);
+  }
+
+  size_t NumInputEpsilons(StateId state) const {
+    // State 0 has no parent, thus no backoff.
+    if (state == 0) return 0;
+    return 1;
+  }
+
+  size_t NumOutputEpsilons(StateId state) const {
+    return NumInputEpsilons(state);
+  }
+
+  StateId NumStates() const {
+    return num_states_;
+  }
+
+  void InitStateIterator(StateIteratorData<A>* data) const {
+    data->base = 0;
+    data->nstates = num_states_;
+  }
+
+  static size_t Storage(uint64 num_states, uint64 num_futures,
+                        uint64 num_final) {
+    uint64 b64;
+    Weight weight;
+    Label label;
+    size_t offset = sizeof(num_states) + sizeof(num_futures) +
+        sizeof(num_final);
+    offset += sizeof(b64) * (
+        BitmapIndex::StorageSize(num_states * 2 + 1) +
+        BitmapIndex::StorageSize(num_futures + num_states + 1) +
+        BitmapIndex::StorageSize(num_states));
+    offset += (num_states + 1) * sizeof(label) + num_futures * sizeof(label);
+    // Pad for alignemnt, see
+    // http://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
+    offset = (offset + sizeof(weight) - 1) & ~(sizeof(weight) - 1);
+    offset += (num_states + 1) * sizeof(weight) + num_final * sizeof(weight) +
+        (num_futures + 1) * sizeof(weight);
+    return offset;
+  }
+
+  void SetInstFuture(StateId state, NGramFstInst<A> *inst) const {
+    if (inst->state_ != state) {
+      inst->state_ = state;
+      const size_t next_zero = future_index_.Select0(state + 1);
+      const size_t this_zero = future_index_.Select0(state);
+      inst->num_futures_ = next_zero - this_zero - 1;
+      inst->offset_ = future_index_.Rank1(future_index_.Select0(state) + 1);
+    }
+  }
+
+  void SetInstNode(NGramFstInst<A> *inst) const {
+    if (inst->node_state_ != inst->state_) {
+      inst->node_state_ = inst->state_;
+      inst->node_ = context_index_.Select1(inst->state_);
+    }
+  }
+
+  void SetInstContext(NGramFstInst<A> *inst) const {
+    SetInstNode(inst);
+    if (inst->context_state_ != inst->state_) {
+      inst->context_state_ = inst->state_;
+      inst->context_.clear();
+      size_t node = inst->node_;
+      while (node != 0) {
+        inst->context_.push_back(context_words_[context_index_.Rank1(node)]);
+        node = context_index_.Select1(context_index_.Rank0(node) - 1);
+      }
+    }
+  }
+
+  // Access to the underlying representation
+  const char* GetData(size_t* data_size) const {
+    *data_size = Storage(num_states_, num_futures_, num_final_);
+    return data_;
+  }
+
+  void Init(const char* data, bool owned);
+
+ private:
+  StateId Transition(const vector<Label> &context, Label future) const;
+
+  // Properties always true for this Fst class.
+  static const uint64 kStaticProperties = kAcceptor | kIDeterministic |
+      kODeterministic | kEpsilons | kIEpsilons | kOEpsilons | kILabelSorted |
+      kOLabelSorted | kWeighted | kCyclic | kInitialAcyclic | kNotTopSorted |
+      kAccessible | kCoAccessible | kNotString | kExpanded;
+  // Current file format version.
+  static const int kFileVersion = 4;
+  // Minimum file format version supported.
+  static const int kMinFileVersion = 4;
+
+  const char* data_;
+  bool owned_;  // True if we own data_
+  uint64 num_states_, num_futures_, num_final_;
+  size_t root_num_children_;
+  const Label *root_children_;
+  size_t root_first_child_;
+  // borrowed references
+  const uint64 *context_, *future_, *final_;
+  const Label *context_words_, *future_words_;
+  const Weight *backoff_, *final_probs_, *future_probs_;
+  BitmapIndex context_index_;
+  BitmapIndex future_index_;
+  BitmapIndex final_index_;
+
+  void operator=(const NGramFstImpl<A> &);  // Disallow
+};
+
+template<typename A>
+NGramFstImpl<A>::NGramFstImpl(const Fst<A> &fst, vector<StateId>* order_out)
+    : data_(0), owned_(false) {
+  typedef A Arc;
+  typedef typename Arc::Label Label;
+  typedef typename Arc::Weight Weight;
+  typedef typename Arc::StateId StateId;
+  SetType("ngram");
+  SetInputSymbols(fst.InputSymbols());
+  SetOutputSymbols(fst.OutputSymbols());
+  SetProperties(kStaticProperties);
+
+  // Check basic requirements for an OpenGRM language model Fst.
+  int64 props = kAcceptor | kIDeterministic | kIEpsilons | kILabelSorted;
+  if (fst.Properties(props, true) != props) {
+    FSTERROR() << "NGramFst only accepts OpenGRM langauge models as input";
+    SetProperties(kError, kError);
+    return;
+  }
+
+  int64 num_states = CountStates(fst);
+  Label* context = new Label[num_states];
+
+  // Find the unigram state by starting from the start state, following
+  // epsilons.
+  StateId unigram = fst.Start();
+  while (1) {
+    ArcIterator<Fst<A> > aiter(fst, unigram);
+    if (aiter.Done()) {
+      FSTERROR() << "Start state has no arcs";
+      SetProperties(kError, kError);
+      return;
+    }
+    if (aiter.Value().ilabel != 0) break;
+    unigram = aiter.Value().nextstate;
+  }
+
+  // Each state's context is determined by the subtree it is under from the
+  // unigram state.
+  queue<pair<StateId, Label> > label_queue;
+  vector<bool> visited(num_states);
+  // Force an epsilon link to the start state.
+  label_queue.push(make_pair(fst.Start(), 0));
+  for (ArcIterator<Fst<A> > aiter(fst, unigram);
+       !aiter.Done(); aiter.Next()) {
+    label_queue.push(make_pair(aiter.Value().nextstate, aiter.Value().ilabel));
+  }
+  // investigate states in breadth first fashion to assign context words.
+  while (!label_queue.empty()) {
+    pair<StateId, Label> &now = label_queue.front();
+    if (!visited[now.first]) {
+      context[now.first] = now.second;
+      visited[now.first] = true;
+      for (ArcIterator<Fst<A> > aiter(fst, now.first);
+           !aiter.Done(); aiter.Next()) {
+        const Arc &arc = aiter.Value();
+        if (arc.ilabel != 0) {
+          label_queue.push(make_pair(arc.nextstate, now.second));
+        }
+      }
+    }
+    label_queue.pop();
+  }
+  visited.clear();
+
+  // The arc from the start state should be assigned an epsilon to put it
+  // in front of the all other labels (which makes Start state 1 after
+  // unigram which is state 0).
+  context[fst.Start()] = 0;
+
+  // Build the tree of contexts fst by reversing the epsilon arcs from fst.
+  VectorFst<Arc> context_fst;
+  uint64 num_final = 0;
+  for (int i = 0; i < num_states; ++i) {
+    if (fst.Final(i) != Weight::Zero()) {
+      ++num_final;
+    }
+    context_fst.SetFinal(context_fst.AddState(), fst.Final(i));
+  }
+  context_fst.SetStart(unigram);
+  context_fst.SetInputSymbols(fst.InputSymbols());
+  context_fst.SetOutputSymbols(fst.OutputSymbols());
+  int64 num_context_arcs = 0;
+  int64 num_futures = 0;
+  for (StateIterator<Fst<A> > siter(fst); !siter.Done(); siter.Next()) {
+    const StateId &state = siter.Value();
+    num_futures += fst.NumArcs(state) - fst.NumInputEpsilons(state);
+    ArcIterator<Fst<A> > aiter(fst, state);
+    if (!aiter.Done()) {
+      const Arc &arc = aiter.Value();
+      // this arc goes from state to arc.nextstate, so create an arc from
+      // arc.nextstate to state to reverse it.
+      if (arc.ilabel == 0) {
+        context_fst.AddArc(arc.nextstate, Arc(context[state], context[state],
+                                              arc.weight, state));
+        num_context_arcs++;
+      }
+    }
+  }
+  if (num_context_arcs != context_fst.NumStates() - 1) {
+    FSTERROR() << "Number of contexts arcs != number of states - 1";
+    SetProperties(kError, kError);
+    return;
+  }
+  if (context_fst.NumStates() != num_states) {
+    FSTERROR() << "Number of contexts != number of states";
+    SetProperties(kError, kError);
+    return;
+  }
+  int64 context_props = context_fst.Properties(kIDeterministic |
+                                               kILabelSorted, true);
+  if (!(context_props & kIDeterministic)) {
+    FSTERROR() << "Input fst is not structured properly";
+    SetProperties(kError, kError);
+    return;
+  }
+  if (!(context_props & kILabelSorted)) {
+     ArcSort(&context_fst, ILabelCompare<Arc>());
+  }
+
+  delete [] context;
+
+  uint64 b64;
+  Weight weight;
+  Label label = kNoLabel;
+  const size_t storage = Storage(num_states, num_futures, num_final);
+  char* data = new char[storage];
+  memset(data, 0, storage);
+  size_t offset = 0;
+  memcpy(data + offset, reinterpret_cast<char *>(&num_states),
+         sizeof(num_states));
+  offset += sizeof(num_states);
+  memcpy(data + offset, reinterpret_cast<char *>(&num_futures),
+         sizeof(num_futures));
+  offset += sizeof(num_futures);
+  memcpy(data + offset, reinterpret_cast<char *>(&num_final),
+         sizeof(num_final));
+  offset += sizeof(num_final);
+  uint64* context_bits = reinterpret_cast<uint64*>(data + offset);
+  offset += BitmapIndex::StorageSize(num_states * 2 + 1) * sizeof(b64);
+  uint64* future_bits = reinterpret_cast<uint64*>(data + offset);
+  offset +=
+      BitmapIndex::StorageSize(num_futures + num_states + 1) * sizeof(b64);
+  uint64* final_bits = reinterpret_cast<uint64*>(data + offset);
+  offset += BitmapIndex::StorageSize(num_states) * sizeof(b64);
+  Label* context_words = reinterpret_cast<Label*>(data + offset);
+  offset += (num_states + 1) * sizeof(label);
+  Label* future_words = reinterpret_cast<Label*>(data + offset);
+  offset += num_futures * sizeof(label);
+  offset = (offset + sizeof(weight) - 1) & ~(sizeof(weight) - 1);
+  Weight* backoff = reinterpret_cast<Weight*>(data + offset);
+  offset += (num_states + 1) * sizeof(weight);
+  Weight* final_probs = reinterpret_cast<Weight*>(data + offset);
+  offset += num_final * sizeof(weight);
+  Weight* future_probs = reinterpret_cast<Weight*>(data + offset);
+  int64 context_arc = 0, future_arc = 0, context_bit = 0, future_bit = 0,
+        final_bit = 0;
+
+  // pseudo-root bits
+  BitmapIndex::Set(context_bits, context_bit++);
+  ++context_bit;
+  context_words[context_arc] = label;
+  backoff[context_arc] = Weight::Zero();
+  context_arc++;
+
+  ++future_bit;
+  if (order_out) {
+    order_out->clear();
+    order_out->resize(num_states);
+  }
+
+  queue<StateId> context_q;
+  context_q.push(context_fst.Start());
+  StateId state_number = 0;
+  while (!context_q.empty()) {
+    const StateId &state = context_q.front();
+    if (order_out) {
+      (*order_out)[state] = state_number;
+    }
+
+    const Weight &final = context_fst.Final(state);
+    if (final != Weight::Zero()) {
+      BitmapIndex::Set(final_bits, state_number);
+      final_probs[final_bit] = final;
+      ++final_bit;
+    }
+
+    for (ArcIterator<VectorFst<A> > aiter(context_fst, state);
+         !aiter.Done(); aiter.Next()) {
+      const Arc &arc = aiter.Value();
+      context_words[context_arc] = arc.ilabel;
+      backoff[context_arc] = arc.weight;
+      ++context_arc;
+      BitmapIndex::Set(context_bits, context_bit++);
+      context_q.push(arc.nextstate);
+    }
+    ++context_bit;
+
+    for (ArcIterator<Fst<A> > aiter(fst, state); !aiter.Done(); aiter.Next()) {
+      const Arc &arc = aiter.Value();
+      if (arc.ilabel != 0) {
+        future_words[future_arc] = arc.ilabel;
+        future_probs[future_arc] = arc.weight;
+        ++future_arc;
+        BitmapIndex::Set(future_bits, future_bit++);
+      }
+    }
+    ++future_bit;
+    ++state_number;
+    context_q.pop();
+  }
+
+  if ((state_number !=  num_states) ||
+      (context_bit != num_states * 2 + 1) ||
+      (context_arc != num_states) ||
+      (future_arc != num_futures) ||
+      (future_bit != num_futures + num_states + 1) ||
+      (final_bit != num_final)) {
+    FSTERROR() << "Structure problems detected during construction";
+    SetProperties(kError, kError);
+    return;
+  }
+
+  Init(data, true /* owned */);
+}
+
+template<typename A>
+inline void NGramFstImpl<A>::Init(const char* data, bool owned) {
+  if (owned_) {
+    delete [] data_;
+  }
+  owned_ = owned;
+  data_ = data;
+  size_t offset = 0;
+  num_states_ = *(reinterpret_cast<const uint64*>(data_ + offset));
+  offset += sizeof(num_states_);
+  num_futures_ = *(reinterpret_cast<const uint64*>(data_ + offset));
+  offset += sizeof(num_futures_);
+  num_final_ = *(reinterpret_cast<const uint64*>(data_ + offset));
+  offset += sizeof(num_final_);
+  uint64 bits;
+  size_t context_bits = num_states_ * 2 + 1;
+  size_t future_bits = num_futures_ + num_states_ + 1;
+  context_ = reinterpret_cast<const uint64*>(data_ + offset);
+  offset += BitmapIndex::StorageSize(context_bits) * sizeof(bits);
+  future_ = reinterpret_cast<const uint64*>(data_ + offset);
+  offset += BitmapIndex::StorageSize(future_bits) * sizeof(bits);
+  final_ = reinterpret_cast<const uint64*>(data_ + offset);
+  offset += BitmapIndex::StorageSize(num_states_ + 1) * sizeof(bits);
+  context_words_ = reinterpret_cast<const Label*>(data_ + offset);
+  offset += (num_states_ + 1) * sizeof(*context_words_);
+  future_words_ = reinterpret_cast<const Label*>(data_ + offset);
+  offset += num_futures_ * sizeof(*future_words_);
+  offset = (offset + sizeof(*backoff_) - 1) & ~(sizeof(*backoff_) - 1);
+  backoff_ = reinterpret_cast<const Weight*>(data_ + offset);
+  offset += (num_states_ + 1) * sizeof(*backoff_);
+  final_probs_ = reinterpret_cast<const Weight*>(data_ + offset);
+  offset += num_final_ * sizeof(*final_probs_);
+  future_probs_ = reinterpret_cast<const Weight*>(data_ + offset);
+
+  context_index_.BuildIndex(context_, context_bits);
+  future_index_.BuildIndex(future_, future_bits);
+  final_index_.BuildIndex(final_, num_states_);
+
+  const size_t node_rank = context_index_.Rank1(0);
+  root_first_child_ = context_index_.Select0(node_rank) + 1;
+  if (context_index_.Get(root_first_child_) == false) {
+    FSTERROR() << "Missing unigrams";
+    SetProperties(kError, kError);
+    return;
+  }
+  const size_t last_child = context_index_.Select0(node_rank + 1) - 1;
+  root_num_children_ = last_child - root_first_child_ + 1;
+  root_children_ = context_words_ + context_index_.Rank1(root_first_child_);
+}
+
+template<typename A>
+inline typename A::StateId NGramFstImpl<A>::Transition(
+        const vector<Label> &context, Label future) const {
+  size_t num_children = root_num_children_;
+  const Label *children = root_children_;
+  const Label *loc = lower_bound(children, children + num_children, future);
+  if (loc == children + num_children || *loc != future) {
+    return context_index_.Rank1(0);
+  }
+  size_t node = root_first_child_ + loc - children;
+  size_t node_rank = context_index_.Rank1(node);
+  size_t first_child = context_index_.Select0(node_rank) + 1;
+  if (context_index_.Get(first_child) == false) {
+    return context_index_.Rank1(node);
+  }
+  size_t last_child = context_index_.Select0(node_rank + 1) - 1;
+  num_children = last_child - first_child + 1;
+  for (int word = context.size() - 1; word >= 0; --word) {
+    children = context_words_ + context_index_.Rank1(first_child);
+    loc = lower_bound(children, children + last_child - first_child + 1,
+                      context[word]);
+    if (loc == children + last_child - first_child + 1 ||
+        *loc != context[word]) {
+      break;
+    }
+    node = first_child + loc - children;
+    node_rank = context_index_.Rank1(node);
+    first_child = context_index_.Select0(node_rank) + 1;
+    if (context_index_.Get(first_child) == false) break;
+    last_child = context_index_.Select0(node_rank + 1) - 1;
+  }
+  return context_index_.Rank1(node);
+}
+
+/*****************************************************************************/
+template<class A>
+class NGramFst : public ImplToExpandedFst<NGramFstImpl<A> > {
+  friend class ArcIterator<NGramFst<A> >;
+  friend class NGramFstMatcher<A>;
+
+ public:
+  typedef A Arc;
+  typedef typename A::StateId StateId;
+  typedef typename A::Label Label;
+  typedef typename A::Weight Weight;
+  typedef NGramFstImpl<A> Impl;
+
+  explicit NGramFst(const Fst<A> &dst)
+      : ImplToExpandedFst<Impl>(new Impl(dst, NULL)) {}
+
+  NGramFst(const Fst<A> &fst, vector<StateId>* order_out)
+      : ImplToExpandedFst<Impl>(new Impl(fst, order_out)) {}
+
+  // Because the NGramFstImpl is a const stateless data structure, there
+  // is never a need to do anything beside copy the reference.
+  NGramFst(const NGramFst<A> &fst, bool safe = false)
+      : ImplToExpandedFst<Impl>(fst, false) {}
+
+  NGramFst() : ImplToExpandedFst<Impl>(new Impl()) {}
+
+  // Non-standard constructor to initialize NGramFst directly from data.
+  NGramFst(const char* data, bool owned) : ImplToExpandedFst<Impl>(new Impl()) {
+    GetImpl()->Init(data, owned);
+  }
+
+  // Get method that gets the data associated with Init().
+  const char* GetData(size_t* data_size) const {
+    return GetImpl()->GetData(data_size);
+  }
+
+  virtual size_t NumArcs(StateId s) const {
+    return GetImpl()->NumArcs(s, &inst_);
+  }
+
+  virtual NGramFst<A>* Copy(bool safe = false) const {
+    return new NGramFst(*this, safe);
+  }
+
+  static NGramFst<A>* Read(istream &strm, const FstReadOptions &opts) {
+    Impl* impl = Impl::Read(strm, opts);
+    return impl ? new NGramFst<A>(impl) : 0;
+  }
+
+  static NGramFst<A>* Read(const string &filename) {
+    if (!filename.empty()) {
+      ifstream strm(filename.c_str(), ifstream::in | ifstream::binary);
+      if (!strm) {
+        LOG(ERROR) << "NGramFst::Read: Can't open file: " << filename;
+        return 0;
+      }
+      return Read(strm, FstReadOptions(filename));
+    } else {
+      return Read(cin, FstReadOptions("standard input"));
+    }
+  }
+
+  virtual bool Write(ostream &strm, const FstWriteOptions &opts) const {
+    return GetImpl()->Write(strm, opts);
+  }
+
+  virtual bool Write(const string &filename) const {
+    return Fst<A>::WriteFile(filename);
+  }
+
+  virtual inline void InitStateIterator(StateIteratorData<A>* data) const {
+    GetImpl()->InitStateIterator(data);
+  }
+
+  virtual inline void InitArcIterator(
+      StateId s, ArcIteratorData<A>* data) const;
+
+  virtual MatcherBase<A>* InitMatcher(MatchType match_type) const {
+    return new NGramFstMatcher<A>(*this, match_type);
+  }
+
+ private:
+  explicit NGramFst(Impl* impl) : ImplToExpandedFst<Impl>(impl) {}
+
+  Impl* GetImpl() const {
+    return
+        ImplToExpandedFst<Impl, ExpandedFst<A> >::GetImpl();
+  }
+
+  void SetImpl(Impl* impl, bool own_impl = true) {
+    ImplToExpandedFst<Impl, Fst<A> >::SetImpl(impl, own_impl);
+  }
+
+  mutable NGramFstInst<A> inst_;
+};
+
+template <class A> inline void
+NGramFst<A>::InitArcIterator(StateId s, ArcIteratorData<A>* data) const {
+  GetImpl()->SetInstFuture(s, &inst_);
+  GetImpl()->SetInstNode(&inst_);
+  data->base = new ArcIterator<NGramFst<A> >(*this, s);
+}
+
+/*****************************************************************************/
+template <class A>
+class NGramFstMatcher : public MatcherBase<A> {
+ public:
+  typedef A Arc;
+  typedef typename A::Label Label;
+  typedef typename A::StateId StateId;
+  typedef typename A::Weight Weight;
+
+  NGramFstMatcher(const NGramFst<A> &fst, MatchType match_type)
+      : fst_(fst), inst_(fst.inst_), match_type_(match_type),
+        current_loop_(false),
+        loop_(kNoLabel, 0, A::Weight::One(), kNoStateId) {
+    if (match_type_ == MATCH_OUTPUT) {
+      swap(loop_.ilabel, loop_.olabel);
+    }
+  }
+
+  NGramFstMatcher(const NGramFstMatcher<A> &matcher, bool safe = false)
+      : fst_(matcher.fst_), inst_(matcher.inst_),
+        match_type_(matcher.match_type_), current_loop_(false),
+        loop_(kNoLabel, 0, A::Weight::One(), kNoStateId) {
+    if (match_type_ == MATCH_OUTPUT) {
+      swap(loop_.ilabel, loop_.olabel);
+    }
+  }
+
+  virtual NGramFstMatcher<A>* Copy(bool safe = false) const {
+    return new NGramFstMatcher<A>(*this, safe);
+  }
+
+  virtual MatchType Type(bool test) const {
+    return match_type_;
+  }
+
+  virtual const Fst<A> &GetFst() const {
+    return fst_;
+  }
+
+  virtual uint64 Properties(uint64 props) const {
+    return props;
+  }
+
+ private:
+  virtual void SetState_(StateId s) {
+    fst_.GetImpl()->SetInstFuture(s, &inst_);
+    current_loop_ = false;
+  }
+
+  virtual bool Find_(Label label) {
+    const Label nolabel = kNoLabel;
+    done_ = true;
+    if (label == 0 || label == nolabel) {
+      if (label == 0) {
+        current_loop_ = true;
+        loop_.nextstate = inst_.state_;
+      }
+      // The unigram state has no epsilon arc.
+      if (inst_.state_ != 0) {
+        arc_.ilabel = arc_.olabel = 0;
+        fst_.GetImpl()->SetInstNode(&inst_);
+        arc_.nextstate = fst_.GetImpl()->context_index_.Rank1(
+            fst_.GetImpl()->context_index_.Select1(
+                fst_.GetImpl()->context_index_.Rank0(inst_.node_) - 1));
+        arc_.weight = fst_.GetImpl()->backoff_[inst_.state_];
+        done_ = false;
+      }
+    } else {
+      const Label *start = fst_.GetImpl()->future_words_ + inst_.offset_;
+      const Label *end = start + inst_.num_futures_;
+      const Label* search = lower_bound(start, end, label);
+      if (search != end && *search == label) {
+        size_t state = search - start;
+        arc_.ilabel = arc_.olabel = label;
+        arc_.weight = fst_.GetImpl()->future_probs_[inst_.offset_ + state];
+        fst_.GetImpl()->SetInstContext(&inst_);
+        arc_.nextstate = fst_.GetImpl()->Transition(inst_.context_, label);
+        done_ = false;
+      }
+    }
+    return !Done_();
+  }
+
+  virtual bool Done_() const {
+    return !current_loop_ && done_;
+  }
+
+  virtual const Arc& Value_() const {
+    return (current_loop_) ? loop_ : arc_;
+  }
+
+  virtual void Next_() {
+    if (current_loop_) {
+      current_loop_ = false;
+    } else {
+      done_ = true;
+    }
+  }
+
+  const NGramFst<A>& fst_;
+  NGramFstInst<A> inst_;
+  MatchType match_type_;             // Supplied by caller
+  bool done_;
+  Arc arc_;
+  bool current_loop_;                // Current arc is the implicit loop
+  Arc loop_;
+};
+
+/*****************************************************************************/
+template<class A>
+class ArcIterator<NGramFst<A> > : public ArcIteratorBase<A> {
+ public:
+  typedef A Arc;
+  typedef typename A::Label Label;
+  typedef typename A::StateId StateId;
+  typedef typename A::Weight Weight;
+
+  ArcIterator(const NGramFst<A> &fst, StateId state)
+      : lazy_(~0), impl_(fst.GetImpl()), i_(0), flags_(kArcValueFlags) {
+    inst_ = fst.inst_;
+    impl_->SetInstFuture(state, &inst_);
+    impl_->SetInstNode(&inst_);
+  }
+
+  bool Done() const {
+    return i_ >= ((inst_.node_ == 0) ? inst_.num_futures_ :
+                  inst_.num_futures_ + 1);
+  }
+
+  const Arc &Value() const {
+    bool eps = (inst_.node_ != 0 && i_ == 0);
+    StateId state = (inst_.node_ == 0) ? i_ : i_ - 1;
+    if (flags_ & lazy_ & (kArcILabelValue | kArcOLabelValue)) {
+      arc_.ilabel =
+          arc_.olabel = eps ? 0 : impl_->future_words_[inst_.offset_ + state];
+      lazy_ &= ~(kArcILabelValue | kArcOLabelValue);
+    }
+    if (flags_ & lazy_ & kArcNextStateValue) {
+      if (eps) {
+        arc_.nextstate = impl_->context_index_.Rank1(
+            impl_->context_index_.Select1(
+                impl_->context_index_.Rank0(inst_.node_) - 1));
+      } else {
+        if (lazy_ & kArcNextStateValue) {
+          impl_->SetInstContext(&inst_);  // first time only.
+        }
+        arc_.nextstate =
+            impl_->Transition(inst_.context_,
+                              impl_->future_words_[inst_.offset_ + state]);
+      }
+      lazy_ &= ~kArcNextStateValue;
+    }
+    if (flags_ & lazy_ & kArcWeightValue) {
+      arc_.weight = eps ?  impl_->backoff_[inst_.state_] :
+          impl_->future_probs_[inst_.offset_ + state];
+      lazy_ &= ~kArcWeightValue;
+    }
+    return arc_;
+  }
+
+  void Next() {
+    ++i_;
+    lazy_ = ~0;
+  }
+
+  size_t Position() const { return i_; }
+
+  void Reset() {
+    i_ = 0;
+    lazy_ = ~0;
+  }
+
+  void Seek(size_t a) {
+    if (i_ != a) {
+      i_ = a;
+      lazy_ = ~0;
+    }
+  }
+
+  uint32 Flags() const {
+    return flags_;
+  }
+
+  void SetFlags(uint32 f, uint32 m) {
+    flags_ &= ~m;
+    flags_ |= (f & kArcValueFlags);
+  }
+
+ private:
+  virtual bool Done_() const { return Done(); }
+  virtual const Arc& Value_() const { return Value(); }
+  virtual void Next_() { Next(); }
+  virtual size_t Position_() const { return Position(); }
+  virtual void Reset_() { Reset(); }
+  virtual void Seek_(size_t a) { Seek(a); }
+  uint32 Flags_() const { return Flags(); }
+  void SetFlags_(uint32 f, uint32 m) { SetFlags(f, m); }
+
+  mutable Arc arc_;
+  mutable uint32 lazy_;
+  const NGramFstImpl<A> *impl_;
+  mutable NGramFstInst<A> inst_;
+
+  size_t i_;
+  uint32 flags_;
+
+  DISALLOW_COPY_AND_ASSIGN(ArcIterator);
+};
+
+/*****************************************************************************/
+// Specialization for NGramFst; see generic version in fst.h
+// for sample usage (but use the ProdLmFst type!). This version
+// should inline.
+template <class A>
+class StateIterator<NGramFst<A> > : public StateIteratorBase<A> {
+  public:
+  typedef typename A::StateId StateId;
+
+  explicit StateIterator(const NGramFst<A> &fst)
+    : s_(0), num_states_(fst.NumStates()) { }
+
+  bool Done() const { return s_ >= num_states_; }
+  StateId Value() const { return s_; }
+  void Next() { ++s_; }
+  void Reset() { s_ = 0; }
+
+ private:
+  virtual bool Done_() const { return Done(); }
+  virtual StateId Value_() const { return Value(); }
+  virtual void Next_() { Next(); }
+  virtual void Reset_() { Reset(); }
+
+  StateId s_, num_states_;
+
+  DISALLOW_COPY_AND_ASSIGN(StateIterator);
+};
+}  // namespace fst
+#endif  // FST_EXTENSIONS_NGRAM_NGRAM_FST_H_
diff --git a/src/include/fst/extensions/ngram/nthbit.h b/src/include/fst/extensions/ngram/nthbit.h
new file mode 100644
index 0000000..d4a9a5a
--- /dev/null
+++ b/src/include/fst/extensions/ngram/nthbit.h
@@ -0,0 +1,46 @@
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+// Copyright 2005-2010 Google, Inc.
+// Author: sorenj@google.com (Jeffrey Sorensen)
+//         dr@google.com (Doug Rohde)
+
+#ifndef FST_EXTENSIONS_NGRAM_NTHBIT_H_
+#define FST_EXTENSIONS_NGRAM_NTHBIT_H_
+
+#include <fst/types.h>
+
+extern uint32 nth_bit_bit_offset[];
+
+inline uint32 nth_bit(uint64 v, uint32 r) {
+  uint32 shift = 0;
+  uint32 c = __builtin_popcount(v & 0xffffffff);
+  uint32 mask = -(r > c);
+  r -= c & mask;
+  shift += (32 & mask);
+
+  c = __builtin_popcount((v >> shift) & 0xffff);
+  mask = -(r > c);
+  r -= c & mask;
+  shift += (16 & mask);
+
+  c = __builtin_popcount((v >> shift) & 0xff);
+  mask = -(r > c);
+  r -= c & mask;
+  shift += (8 & mask);
+
+  return shift + ((nth_bit_bit_offset[(v >> shift) & 0xff] >>
+                   ((r - 1) << 2)) & 0xf);
+}
+
+#endif  // FST_EXTENSIONS_NGRAM_NTHBIT_H_
diff --git a/src/include/fst/extensions/pdt/collection.h b/src/include/fst/extensions/pdt/collection.h
index 26be504..24a443f 100644
--- a/src/include/fst/extensions/pdt/collection.h
+++ b/src/include/fst/extensions/pdt/collection.h
@@ -16,7 +16,7 @@
 // Author: riley@google.com (Michael Riley)
 //
 // \file
-// Class to store a collection of sets with elements of type T.
+// Class to store a collection of ordered (multi-)sets with elements of type T.
 
 #ifndef FST_EXTENSIONS_PDT_COLLECTION_H__
 #define FST_EXTENSIONS_PDT_COLLECTION_H__
@@ -29,11 +29,11 @@ using std::vector;
 
 namespace fst {
 
-// Stores a collection of non-empty sets with elements of type T. A
-// default constructor, equality ==, a total order <, and an STL-style
-// hash class must be defined on the elements. Provides signed
-// integer ID (of type I) of each unique set. The IDs are allocated
-// starting from 0 in order.
+// Stores a collection of non-empty, ordered (multi-)sets with elements
+// of type T. A default constructor, equality ==, and an STL-style
+// hash class must be defined on the elements. Provides signed integer
+// ID (of type I) of each unique set. The IDs are allocated starting
+// from 0 in order.
 template <class I, class T>
 class Collection {
  public:
@@ -80,31 +80,34 @@ class Collection {
 
   Collection() {}
 
-  // Lookups integer ID from set. If it doesn't exist, then adds it.
-  // Set elements should be in strict order (and therefore unique).
-  I FindId(const vector<T> &set) {
+  // Lookups integer ID from ordered multi-set. If it doesn't exist
+  // and 'insert' is true, then adds it. Otherwise returns -1.
+  I FindId(const vector<T> &set, bool insert = true) {
     I node_id = kNoNodeId;
     for (ssize_t i = set.size() - 1; i >= 0; --i) {
       Node node(node_id, set[i]);
-      node_id = node_table_.FindId(node);
+      node_id = node_table_.FindId(node, insert);
+      if (node_id == -1) break;
     }
     return node_id;
   }
 
-  // Finds set given integer ID. Returns true if ID corresponds
-  // to set. Use iterators below to traverse result.
+  // Finds ordered (multi-)set given integer ID. Returns set iterator
+  // to traverse result.
   SetIterator FindSet(I id) {
-    if (id < 0 && id >= node_table_.Size()) {
+    if (id < 0 || id >= node_table_.Size()) {
       return SetIterator(kNoNodeId, Node(kNoNodeId, T()), &node_table_);
     } else {
       return SetIterator(id, node_table_.FindEntry(id), &node_table_);
     }
   }
 
+  I Size() const { return node_table_.Size(); }
+
  private:
   static const I kNoNodeId;
   static const size_t kPrime;
-  static std::tr1::hash<T> hash_;
+  static std::hash<T> hash_;
 
   NodeTable node_table_;
 
@@ -115,7 +118,7 @@ template<class I, class T> const I Collection<I, T>::kNoNodeId = -1;
 
 template <class I, class T> const size_t Collection<I, T>::kPrime = 7853;
 
-template <class I, class T> std::tr1::hash<T> Collection<I, T>::hash_;
+template <class I, class T> std::hash<T> Collection<I, T>::hash_;
 
 }  // namespace fst
 
diff --git a/src/include/fst/extensions/pdt/info.h b/src/include/fst/extensions/pdt/info.h
index ef9a860..55e76c4 100644
--- a/src/include/fst/extensions/pdt/info.h
+++ b/src/include/fst/extensions/pdt/info.h
@@ -24,7 +24,7 @@
 #include <unordered_map>
 using std::tr1::unordered_map;
 using std::tr1::unordered_multimap;
-#include <tr1/unordered_set>
+#include <unordered_set>
 using std::tr1::unordered_set;
 using std::tr1::unordered_multiset;
 #include <vector>
diff --git a/src/include/fst/extensions/pdt/paren.h b/src/include/fst/extensions/pdt/paren.h
index 7b9887f..a9d30c5 100644
--- a/src/include/fst/extensions/pdt/paren.h
+++ b/src/include/fst/extensions/pdt/paren.h
@@ -26,7 +26,7 @@
 #include <unordered_map>
 using std::tr1::unordered_map;
 using std::tr1::unordered_multimap;
-#include <tr1/unordered_set>
+#include <unordered_set>
 using std::tr1::unordered_set;
 using std::tr1::unordered_multiset;
 #include <set>
@@ -144,7 +144,8 @@ class PdtParenReachable {
                     const vector<pair<Label, Label> > &parens, bool close)
       : fst_(fst),
         parens_(parens),
-        close_(close) {
+        close_(close),
+        error_(false) {
     for (Label i = 0; i < parens.size(); ++i) {
       const pair<Label, Label>  &p = parens[i];
       paren_id_map_[p.first] = i;
@@ -155,12 +156,18 @@ class PdtParenReachable {
       StateId start = fst.Start();
       if (start == kNoStateId)
         return;
-      DFSearch(start, start);
+      if (!DFSearch(start)) {
+        FSTERROR() << "PdtReachable: Underlying cyclicity not supported";
+        error_ = true;
+      }
     } else {
       FSTERROR() << "PdtParenReachable: open paren info not implemented";
+      error_ = true;
     }
   }
 
+  bool const Error() { return error_; }
+
   // Given a state ID, returns an iterator over paren IDs
   // for close (open) parens reachable from that state along balanced
   // paths.
@@ -194,7 +201,7 @@ class PdtParenReachable {
  private:
   // DFS that gathers paren and state set information.
   // Bool returns false when cycle detected.
-  bool DFSearch(StateId s, StateId start);
+  bool DFSearch(StateId s);
 
   // Unions state sets together gathered by the DFS.
   void ComputeStateSet(StateId s);
@@ -212,12 +219,13 @@ class PdtParenReachable {
   vector<char> state_color_;                          // DFS state
   mutable Collection<ssize_t, StateId> state_sets_;   // Reachable states -> ID
   StateSetMap set_map_;                               // ID -> Reachable states
+  bool error_;
   DISALLOW_COPY_AND_ASSIGN(PdtParenReachable);
 };
 
 // DFS that gathers paren and state set information.
 template <class A>
-bool PdtParenReachable<A>::DFSearch(StateId s, StateId start) {
+bool PdtParenReachable<A>::DFSearch(StateId s) {
   if (s >= state_color_.size())
     state_color_.resize(s + 1, kDfsWhite);
 
@@ -239,7 +247,8 @@ bool PdtParenReachable<A>::DFSearch(StateId s, StateId start) {
     if (pit != paren_id_map_.end()) {               // paren?
       Label paren_id = pit->second;
       if (arc.ilabel == parens_[paren_id].first) {  // open paren
-        DFSearch(arc.nextstate, arc.nextstate);
+        if (!DFSearch(arc.nextstate))
+          return false;
         for (SetIterator set_iter = FindStates(paren_id, arc.nextstate);
              !set_iter.Done(); set_iter.Next()) {
           for (ParenArcIterator paren_arc_iter =
@@ -247,15 +256,14 @@ bool PdtParenReachable<A>::DFSearch(StateId s, StateId start) {
                !paren_arc_iter.Done();
                paren_arc_iter.Next()) {
             const A &cparc = paren_arc_iter.Value();
-            DFSearch(cparc.nextstate, start);
+            if (!DFSearch(cparc.nextstate))
+              return false;
           }
         }
       }
     } else {                                       // non-paren
-      if(!DFSearch(arc.nextstate, start)) {
-        FSTERROR() << "PdtReachable: Underlying cyclicity not supported";
-        return true;
-      }
+      if(!DFSearch(arc.nextstate))
+        return false;
     }
   }
   ComputeStateSet(s);
diff --git a/src/include/fst/extensions/pdt/shortest-path.h b/src/include/fst/extensions/pdt/shortest-path.h
index e90471b..85f94b8 100644
--- a/src/include/fst/extensions/pdt/shortest-path.h
+++ b/src/include/fst/extensions/pdt/shortest-path.h
@@ -28,7 +28,7 @@
 #include <unordered_map>
 using std::tr1::unordered_map;
 using std::tr1::unordered_multimap;
-#include <tr1/unordered_set>
+#include <unordered_set>
 using std::tr1::unordered_set;
 using std::tr1::unordered_multiset;
 #include <stack>
@@ -387,7 +387,6 @@ class PdtShortestPath {
   typedef typename SpData::SearchState SearchState;
   typedef typename SpData::ParenSpec ParenSpec;
 
-  typedef typename PdtParenReachable<Arc>::SetIterator StateSetIterator;
   typedef typename PdtBalanceData<Arc>::SetIterator CloseSourceIterator;
 
   PdtShortestPath(const Fst<Arc> &ifst,
@@ -403,7 +402,7 @@ class PdtShortestPath {
 
     if ((Weight::Properties() & (kPath | kRightSemiring))
         != (kPath | kRightSemiring)) {
-      FSTERROR() << "SingleShortestPath: Weight needs to have the path"
+      FSTERROR() << "PdtShortestPath: Weight needs to have the path"
                  << " property and be right distributive: " << Weight::Type();
       error_ = true;
     }
@@ -440,6 +439,7 @@ class PdtShortestPath {
   static const Arc kNoArc;
   static const uint8 kEnqueued;
   static const uint8 kExpanded;
+  static const uint8 kFinished;
   const uint8 kFinal;
 
  public:
@@ -543,6 +543,7 @@ void PdtShortestPath<Arc, Queue>::GetDistance(StateId start) {
     ProcArcs(s);
     sp_data_.SetFlags(s, kExpanded, kExpanded);
   }
+  sp_data_.SetFlags(q, kFinished, kFinished);
   balance_data_.FinishInsert(start);
   sp_data_.GC(start);
 }
@@ -607,7 +608,11 @@ void PdtShortestPath<Arc, Queue>::ProcOpenParen(
       Queue *state_queue = state_queue_;
       GetDistance(d.start);
       state_queue_ = state_queue;
+    } else if (!(sp_data_.Flags(d) & kFinished)) {
+      FSTERROR() << "PdtShortestPath: open parenthesis recursion: not bounded stack";
+      error_ = true;
     }
+
     for (CloseSourceIterator set_iter =
              balance_data_.Find(paren_id, arc.nextstate);
          !set_iter.Done(); set_iter.Next()) {
@@ -765,6 +770,9 @@ template<class Arc, class Queue>
 const uint8 PdtShortestPath<Arc, Queue>::kExpanded = 0x20;
 
 template<class Arc, class Queue>
+const uint8 PdtShortestPath<Arc, Queue>::kFinished = 0x40;
+
+template<class Arc, class Queue>
 void ShortestPath(const Fst<Arc> &ifst,
                   const vector<pair<typename Arc::Label,
                                     typename Arc::Label> > &parens,