Merge branch 'develop' into update_url

README.md

@@ -14,8 +14,8 @@
 - [Hyper-parameters Tuning](#hyper-parameters-tuning)
 - [Training for Mandarin Language](#training-for-mandarin-language)
 - [Trying Live Demo with Your Own Voice](#trying-live-demo-with-your-own-voice)
-- [Experiments and Benchmarks](#experiments-and-benchmarks)
 - [Released Models](#released-models)
+- [Experiments and Benchmarks](#experiments-and-benchmarks)
 - [Questions and Help](#questions-and-help)
 
 ## Prerequisites
@@ -466,9 +466,21 @@ Test Set                | Aishell Model     | Internal Mandarin Model
 Aishell-Test            |   X.X             |   X.X
 Baidu-Mandarin-Test     |   X.X             |   X.X
 
-#### Multiple GPU Efficiency
+#### Acceleration with Multi-GPUs
+
+We compare the training time with 1, 2, 4, 8, 16 Tesla K40m GPUs (with a subset of LibriSpeech samples whose audio durations are between 6.0 and 7.0 seconds).  And it shows that a **near-linear** acceleration with multiple GPUs has been achieved. In the following figure, the time (in seconds) used for training is plotted on the blue bars.
+
+<img src="docs/images/multi_gpu_speedup.png" width=450><br/>
+
+| # of GPU  | Acceleration Rate |
+| --------  | --------------:   |
+| 1         | 1.00 X |
+| 2         | 1.97 X |
+| 4         | 3.74 X |
+| 8         | 6.21 X |
+|16         | 10.70 X |
 
-TODO: To Be Added
+`tools/profile.sh` provides such a profiling tool.
 
 ## Questions and Help
 

model_utils/decoder.py → decoders/decoders_deprecated.py

@@ -42,8 +42,8 @@ def ctc_greedy_decoder(probs_seq, vocabulary):
 def ctc_beam_search_decoder(probs_seq,
                             beam_size,
                             vocabulary,
-                            blank_id,
                             cutoff_prob=1.0,
+                            cutoff_top_n=40,
                             ext_scoring_func=None,
                             nproc=False):
     """CTC Beam search decoder.
@@ -66,8 +66,6 @@ def ctc_beam_search_decoder(probs_seq,
     :type beam_size: int
     :param vocabulary: Vocabulary list.
     :type vocabulary: list
-    :param blank_id: ID of blank.
-    :type blank_id: int
     :param cutoff_prob: Cutoff probability in pruning,
                         default 1.0, no pruning.
     :type cutoff_prob: float
@@ -87,9 +85,8 @@ def ctc_beam_search_decoder(probs_seq,
             raise ValueError("The shape of prob_seq does not match with the "
                              "shape of the vocabulary.")
 
-    # blank_id check
-    if not blank_id < len(probs_seq[0]):
-        raise ValueError("blank_id shouldn't be greater than probs dimension")
+    # blank_id assign
+    blank_id = len(vocabulary)
 
     # If the decoder called in the multiprocesses, then use the global scorer
     # instantiated in ctc_beam_search_decoder_batch().
@@ -114,7 +111,7 @@ def ctc_beam_search_decoder(probs_seq,
         prob_idx = list(enumerate(probs_seq[time_step]))
         cutoff_len = len(prob_idx)
         #If pruning is enabled
-        if cutoff_prob < 1.0:
+        if cutoff_prob < 1.0 or cutoff_top_n < cutoff_len:
             prob_idx = sorted(prob_idx, key=lambda asd: asd[1], reverse=True)
             cutoff_len, cum_prob = 0, 0.0
             for i in xrange(len(prob_idx)):
@@ -122,6 +119,7 @@ def ctc_beam_search_decoder(probs_seq,
                 cutoff_len += 1
                 if cum_prob >= cutoff_prob:
                     break
+            cutoff_len = min(cutoff_len, cutoff_top_n)
             prob_idx = prob_idx[0:cutoff_len]
 
         for l in prefix_set_prev:
@@ -191,9 +189,9 @@ def ctc_beam_search_decoder(probs_seq,
 def ctc_beam_search_decoder_batch(probs_split,
                                   beam_size,
                                   vocabulary,
-                                  blank_id,
                                   num_processes,
                                   cutoff_prob=1.0,
+                                  cutoff_top_n=40,
                                   ext_scoring_func=None):
     """CTC beam search decoder using multiple processes.
 
@@ -204,8 +202,6 @@ def ctc_beam_search_decoder_batch(probs_split,
     :type beam_size: int
     :param vocabulary: Vocabulary list.
     :type vocabulary: list
-    :param blank_id: ID of blank.
-    :type blank_id: int
     :param num_processes: Number of parallel processes.
     :type num_processes: int
     :param cutoff_prob: Cutoff probability in pruning,
@@ -232,8 +228,8 @@ def ctc_beam_search_decoder_batch(probs_split,
     pool = multiprocessing.Pool(processes=num_processes)
     results = []
     for i, probs_list in enumerate(probs_split):
-        args = (probs_list, beam_size, vocabulary, blank_id, cutoff_prob, None,
-                nproc)
+        args = (probs_list, beam_size, vocabulary, cutoff_prob, cutoff_top_n,
+                None, nproc)
         results.append(pool.apply_async(ctc_beam_search_decoder, args))
 
     pool.close()

model_utils/lm_scorer.py → decoders/scorer_deprecated.py

@@ -8,7 +8,7 @@ import kenlm
 import numpy as np
 
 
-class LmScorer(object):
+class Scorer(object):
     """External scorer to evaluate a prefix or whole sentence in
        beam search decoding, including the score from n-gram language
        model and word count.

decoders/swig/ctc_beam_search_decoder.cpp

+#include "ctc_beam_search_decoder.h"
+
+#include <algorithm>
+#include <cmath>
+#include <iostream>
+#include <limits>
+#include <map>
+#include <utility>
+
+#include "ThreadPool.h"
+#include "fst/fstlib.h"
+
+#include "decoder_utils.h"
+#include "path_trie.h"
+
+using FSTMATCH = fst::SortedMatcher<fst::StdVectorFst>;
+
+std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
+    const std::vector<std::vector<double>> &probs_seq,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size,
+    double cutoff_prob,
+    size_t cutoff_top_n,
+    Scorer *ext_scorer) {
+  // dimension check
+  size_t num_time_steps = probs_seq.size();
+  for (size_t i = 0; i < num_time_steps; ++i) {
+    VALID_CHECK_EQ(probs_seq[i].size(),
+                   vocabulary.size() + 1,
+                   "The shape of probs_seq does not match with "
+                   "the shape of the vocabulary");
+  }
+
+  // assign blank id
+  size_t blank_id = vocabulary.size();
+
+  // assign space id
+  auto it = std::find(vocabulary.begin(), vocabulary.end(), " ");
+  int space_id = it - vocabulary.begin();
+  // if no space in vocabulary
+  if ((size_t)space_id >= vocabulary.size()) {
+    space_id = -2;
+  }
+
+  // init prefixes' root
+  PathTrie root;
+  root.score = root.log_prob_b_prev = 0.0;
+  std::vector<PathTrie *> prefixes;
+  prefixes.push_back(&root);
+
+  if (ext_scorer != nullptr && !ext_scorer->is_character_based()) {
+    auto fst_dict = static_cast<fst::StdVectorFst *>(ext_scorer->dictionary);
+    fst::StdVectorFst *dict_ptr = fst_dict->Copy(true);
+    root.set_dictionary(dict_ptr);
+    auto matcher = std::make_shared<FSTMATCH>(*dict_ptr, fst::MATCH_INPUT);
+    root.set_matcher(matcher);
+  }
+
+  // prefix search over time
+  for (size_t time_step = 0; time_step < num_time_steps; ++time_step) {
+    auto &prob = probs_seq[time_step];
+
+    float min_cutoff = -NUM_FLT_INF;
+    bool full_beam = false;
+    if (ext_scorer != nullptr) {
+      size_t num_prefixes = std::min(prefixes.size(), beam_size);
+      std::sort(
+          prefixes.begin(), prefixes.begin() + num_prefixes, prefix_compare);
+      min_cutoff = prefixes[num_prefixes - 1]->score +
+                   std::log(prob[blank_id]) - std::max(0.0, ext_scorer->beta);
+      full_beam = (num_prefixes == beam_size);
+    }
+
+    std::vector<std::pair<size_t, float>> log_prob_idx =
+        get_pruned_log_probs(prob, cutoff_prob, cutoff_top_n);
+    // loop over chars
+    for (size_t index = 0; index < log_prob_idx.size(); index++) {
+      auto c = log_prob_idx[index].first;
+      auto log_prob_c = log_prob_idx[index].second;
+
+      for (size_t i = 0; i < prefixes.size() && i < beam_size; ++i) {
+        auto prefix = prefixes[i];
+        if (full_beam && log_prob_c + prefix->score < min_cutoff) {
+          break;
+        }
+        // blank
+        if (c == blank_id) {
+          prefix->log_prob_b_cur =
+              log_sum_exp(prefix->log_prob_b_cur, log_prob_c + prefix->score);
+          continue;
+        }
+        // repeated character
+        if (c == prefix->character) {
+          prefix->log_prob_nb_cur = log_sum_exp(
+              prefix->log_prob_nb_cur, log_prob_c + prefix->log_prob_nb_prev);
+        }
+        // get new prefix
+        auto prefix_new = prefix->get_path_trie(c);
+
+        if (prefix_new != nullptr) {
+          float log_p = -NUM_FLT_INF;
+
+          if (c == prefix->character &&
+              prefix->log_prob_b_prev > -NUM_FLT_INF) {
+            log_p = log_prob_c + prefix->log_prob_b_prev;
+          } else if (c != prefix->character) {
+            log_p = log_prob_c + prefix->score;
+          }
+
+          // language model scoring
+          if (ext_scorer != nullptr &&
+              (c == space_id || ext_scorer->is_character_based())) {
+            PathTrie *prefix_toscore = nullptr;
+            // skip scoring the space
+            if (ext_scorer->is_character_based()) {
+              prefix_toscore = prefix_new;
+            } else {
+              prefix_toscore = prefix;
+            }
+
+            double score = 0.0;
+            std::vector<std::string> ngram;
+            ngram = ext_scorer->make_ngram(prefix_toscore);
+            score = ext_scorer->get_log_cond_prob(ngram) * ext_scorer->alpha;
+            log_p += score;
+            log_p += ext_scorer->beta;
+          }
+          prefix_new->log_prob_nb_cur =
+              log_sum_exp(prefix_new->log_prob_nb_cur, log_p);
+        }
+      }  // end of loop over prefix
+    }    // end of loop over vocabulary
+
+    prefixes.clear();
+    // update log probs
+    root.iterate_to_vec(prefixes);
+
+    // only preserve top beam_size prefixes
+    if (prefixes.size() >= beam_size) {
+      std::nth_element(prefixes.begin(),
+                       prefixes.begin() + beam_size,
+                       prefixes.end(),
+                       prefix_compare);
+      for (size_t i = beam_size; i < prefixes.size(); ++i) {
+        prefixes[i]->remove();
+      }
+    }
+  }  // end of loop over time
+
+  // compute aproximate ctc score as the return score, without affecting the
+  // return order of decoding result. To delete when decoder gets stable.
+  for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
+    double approx_ctc = prefixes[i]->score;
+    if (ext_scorer != nullptr) {
+      std::vector<int> output;
+      prefixes[i]->get_path_vec(output);
+      auto prefix_length = output.size();
+      auto words = ext_scorer->split_labels(output);
+      // remove word insert
+      approx_ctc = approx_ctc - prefix_length * ext_scorer->beta;
+      // remove language model weight:
+      approx_ctc -= (ext_scorer->get_sent_log_prob(words)) * ext_scorer->alpha;
+    }
+    prefixes[i]->approx_ctc = approx_ctc;
+  }
+
+  return get_beam_search_result(prefixes, vocabulary, beam_size);
+}
+
+
+std::vector<std::vector<std::pair<double, std::string>>>
+ctc_beam_search_decoder_batch(
+    const std::vector<std::vector<std::vector<double>>> &probs_split,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size,
+    size_t num_processes,
+    double cutoff_prob,
+    size_t cutoff_top_n,
+    Scorer *ext_scorer) {
+  VALID_CHECK_GT(num_processes, 0, "num_processes must be nonnegative!");
+  // thread pool
+  ThreadPool pool(num_processes);
+  // number of samples
+  size_t batch_size = probs_split.size();
+
+  // enqueue the tasks of decoding
+  std::vector<std::future<std::vector<std::pair<double, std::string>>>> res;
+  for (size_t i = 0; i < batch_size; ++i) {
+    res.emplace_back(pool.enqueue(ctc_beam_search_decoder,
+                                  probs_split[i],
+                                  vocabulary,
+                                  beam_size,
+                                  cutoff_prob,
+                                  cutoff_top_n,
+                                  ext_scorer));
+  }
+
+  // get decoding results
+  std::vector<std::vector<std::pair<double, std::string>>> batch_results;
+  for (size_t i = 0; i < batch_size; ++i) {
+    batch_results.emplace_back(res[i].get());
+  }
+  return batch_results;
+}

decoders/swig/ctc_beam_search_decoder.h

+#ifndef CTC_BEAM_SEARCH_DECODER_H_
+#define CTC_BEAM_SEARCH_DECODER_H_
+
+#include <string>
+#include <utility>
+#include <vector>
+
+#include "scorer.h"
+
+/* CTC Beam Search Decoder
+
+ * Parameters:
+ *     probs_seq: 2-D vector that each element is a vector of probabilities
+ *               over vocabulary of one time step.
+ *     vocabulary: A vector of vocabulary.
+ *     beam_size: The width of beam search.
+ *     cutoff_prob: Cutoff probability for pruning.
+ *     cutoff_top_n: Cutoff number for pruning.
+ *     ext_scorer: External scorer to evaluate a prefix, which consists of
+ *                 n-gram language model scoring and word insertion term.
+ *                 Default null, decoding the input sample without scorer.
+ * Return:
+ *     A vector that each element is a pair of score  and decoding result,
+ *     in desending order.
+*/
+std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
+    const std::vector<std::vector<double>> &probs_seq,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size,
+    double cutoff_prob = 1.0,
+    size_t cutoff_top_n = 40,
+    Scorer *ext_scorer = nullptr);
+
+/* CTC Beam Search Decoder for batch data
+
+ * Parameters:
+ *     probs_seq: 3-D vector that each element is a 2-D vector that can be used
+ *                by ctc_beam_search_decoder().
+ *     vocabulary: A vector of vocabulary.
+ *     beam_size: The width of beam search.
+ *     num_processes: Number of threads for beam search.
+ *     cutoff_prob: Cutoff probability for pruning.
+ *     cutoff_top_n: Cutoff number for pruning.
+ *     ext_scorer: External scorer to evaluate a prefix, which consists of
+ *                 n-gram language model scoring and word insertion term.
+ *                 Default null, decoding the input sample without scorer.
+ * Return:
+ *     A 2-D vector that each element is a vector of beam search decoding
+ *     result for one audio sample.
+*/
+std::vector<std::vector<std::pair<double, std::string>>>
+ctc_beam_search_decoder_batch(
+    const std::vector<std::vector<std::vector<double>>> &probs_split,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size,
+    size_t num_processes,
+    double cutoff_prob = 1.0,
+    size_t cutoff_top_n = 40,
+    Scorer *ext_scorer = nullptr);
+
+#endif  // CTC_BEAM_SEARCH_DECODER_H_

decoders/swig/ctc_greedy_decoder.cpp

+#include "ctc_greedy_decoder.h"
+#include "decoder_utils.h"
+
+std::string ctc_greedy_decoder(
+    const std::vector<std::vector<double>> &probs_seq,
+    const std::vector<std::string> &vocabulary) {
+  // dimension check
+  size_t num_time_steps = probs_seq.size();
+  for (size_t i = 0; i < num_time_steps; ++i) {
+    VALID_CHECK_EQ(probs_seq[i].size(),
+                   vocabulary.size() + 1,
+                   "The shape of probs_seq does not match with "
+                   "the shape of the vocabulary");
+  }
+
+  size_t blank_id = vocabulary.size();
+
+  std::vector<size_t> max_idx_vec(num_time_steps, 0);
+  std::vector<size_t> idx_vec;
+  for (size_t i = 0; i < num_time_steps; ++i) {
+    double max_prob = 0.0;
+    size_t max_idx = 0;
+    const std::vector<double> &probs_step = probs_seq[i];
+    for (size_t j = 0; j < probs_step.size(); ++j) {
+      if (max_prob < probs_step[j]) {
+        max_idx = j;
+        max_prob = probs_step[j];
+      }
+    }
+    // id with maximum probability in current time step
+    max_idx_vec[i] = max_idx;
+    // deduplicate
+    if ((i == 0) || ((i > 0) && max_idx_vec[i] != max_idx_vec[i - 1])) {
+      idx_vec.push_back(max_idx_vec[i]);
+    }
+  }
+
+  std::string best_path_result;
+  for (size_t i = 0; i < idx_vec.size(); ++i) {
+    if (idx_vec[i] != blank_id) {
+      best_path_result += vocabulary[idx_vec[i]];
+    }
+  }
+  return best_path_result;
+}

decoders/swig/ctc_greedy_decoder.h

+#ifndef CTC_GREEDY_DECODER_H
+#define CTC_GREEDY_DECODER_H
+
+#include <string>
+#include <vector>
+
+/* CTC Greedy (Best Path) Decoder
+ *
+ * Parameters:
+ *     probs_seq: 2-D vector that each element is a vector of probabilities
+ *               over vocabulary of one time step.
+ *     vocabulary: A vector of vocabulary.
+ * Return:
+ *     The decoding result in string
+ */
+std::string ctc_greedy_decoder(
+    const std::vector<std::vector<double>>& probs_seq,
+    const std::vector<std::string>& vocabulary);
+
+#endif  // CTC_GREEDY_DECODER_H

decoders/swig/decoder_utils.cpp

+#include "decoder_utils.h"
+
+#include <algorithm>
+#include <cmath>
+#include <limits>
+
+std::vector<std::pair<size_t, float>> get_pruned_log_probs(
+    const std::vector<double> &prob_step,
+    double cutoff_prob,
+    size_t cutoff_top_n) {
+  std::vector<std::pair<int, double>> prob_idx;
+  for (size_t i = 0; i < prob_step.size(); ++i) {
+    prob_idx.push_back(std::pair<int, double>(i, prob_step[i]));
+  }
+  // pruning of vacobulary
+  size_t cutoff_len = prob_step.size();
+  if (cutoff_prob < 1.0 || cutoff_top_n < cutoff_len) {
+    std::sort(
+        prob_idx.begin(), prob_idx.end(), pair_comp_second_rev<int, double>);
+    if (cutoff_prob < 1.0) {
+      double cum_prob = 0.0;
+      cutoff_len = 0;
+      for (size_t i = 0; i < prob_idx.size(); ++i) {
+        cum_prob += prob_idx[i].second;
+        cutoff_len += 1;
+        if (cum_prob >= cutoff_prob || cutoff_len >= cutoff_top_n) break;
+      }
+    }
+    prob_idx = std::vector<std::pair<int, double>>(
+        prob_idx.begin(), prob_idx.begin() + cutoff_len);
+  }
+  std::vector<std::pair<size_t, float>> log_prob_idx;
+  for (size_t i = 0; i < cutoff_len; ++i) {
+    log_prob_idx.push_back(std::pair<int, float>(
+        prob_idx[i].first, log(prob_idx[i].second + NUM_FLT_MIN)));
+  }
+  return log_prob_idx;
+}
+
+
+std::vector<std::pair<double, std::string>> get_beam_search_result(
+    const std::vector<PathTrie *> &prefixes,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size) {
+  // allow for the post processing
+  std::vector<PathTrie *> space_prefixes;
+  if (space_prefixes.empty()) {
+    for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
+      space_prefixes.push_back(prefixes[i]);
+    }
+  }
+
+  std::sort(space_prefixes.begin(), space_prefixes.end(), prefix_compare);
+  std::vector<std::pair<double, std::string>> output_vecs;
+  for (size_t i = 0; i < beam_size && i < space_prefixes.size(); ++i) {
+    std::vector<int> output;
+    space_prefixes[i]->get_path_vec(output);
+    // convert index to string
+    std::string output_str;
+    for (size_t j = 0; j < output.size(); j++) {
+      output_str += vocabulary[output[j]];
+    }
+    std::pair<double, std::string> output_pair(-space_prefixes[i]->approx_ctc,
+                                               output_str);
+    output_vecs.emplace_back(output_pair);
+  }
+
+  return output_vecs;
+}
+
+size_t get_utf8_str_len(const std::string &str) {
+  size_t str_len = 0;
+  for (char c : str) {
+    str_len += ((c & 0xc0) != 0x80);
+  }
+  return str_len;
+}
+
+std::vector<std::string> split_utf8_str(const std::string &str) {
+  std::vector<std::string> result;
+  std::string out_str;
+
+  for (char c : str) {
+    if ((c & 0xc0) != 0x80)  // new UTF-8 character
+    {
+      if (!out_str.empty()) {
+        result.push_back(out_str);
+        out_str.clear();
+      }
+    }
+
+    out_str.append(1, c);
+  }
+  result.push_back(out_str);
+  return result;
+}
+
+std::vector<std::string> split_str(const std::string &s,
+                                   const std::string &delim) {
+  std::vector<std::string> result;
+  std::size_t start = 0, delim_len = delim.size();
+  while (true) {
+    std::size_t end = s.find(delim, start);
+    if (end == std::string::npos) {
+      if (start < s.size()) {
+        result.push_back(s.substr(start));
+      }
+      break;
+    }
+    if (end > start) {
+      result.push_back(s.substr(start, end - start));
+    }
+    start = end + delim_len;
+  }
+  return result;
+}
+
+bool prefix_compare(const PathTrie *x, const PathTrie *y) {
+  if (x->score == y->score) {
+    if (x->character == y->character) {
+      return false;
+    } else {
+      return (x->character < y->character);
+    }
+  } else {
+    return x->score > y->score;
+  }
+}
+
+void add_word_to_fst(const std::vector<int> &word,
+                     fst::StdVectorFst *dictionary) {
+  if (dictionary->NumStates() == 0) {
+    fst::StdVectorFst::StateId start = dictionary->AddState();
+    assert(start == 0);
+    dictionary->SetStart(start);
+  }
+  fst::StdVectorFst::StateId src = dictionary->Start();
+  fst::StdVectorFst::StateId dst;
+  for (auto c : word) {
+    dst = dictionary->AddState();
+    dictionary->AddArc(src, fst::StdArc(c, c, 0, dst));
+    src = dst;
+  }
+  dictionary->SetFinal(dst, fst::StdArc::Weight::One());
+}
+
+bool add_word_to_dictionary(
+    const std::string &word,
+    const std::unordered_map<std::string, int> &char_map,
+    bool add_space,
+    int SPACE_ID,
+    fst::StdVectorFst *dictionary) {
+  auto characters = split_utf8_str(word);
+
+  std::vector<int> int_word;
+
+  for (auto &c : characters) {
+    if (c == " ") {
+      int_word.push_back(SPACE_ID);
+    } else {
+      auto int_c = char_map.find(c);
+      if (int_c != char_map.end()) {
+        int_word.push_back(int_c->second);
+      } else {
+        return false;  // return without adding
+      }
+    }
+  }
+
+  if (add_space) {
+    int_word.push_back(SPACE_ID);
+  }
+
+  add_word_to_fst(int_word, dictionary);
+  return true;  // return with successful adding
+}

decoders/swig/decoder_utils.h

+#ifndef DECODER_UTILS_H_
+#define DECODER_UTILS_H_
+
+#include <utility>
+#include "fst/log.h"
+#include "path_trie.h"
+
+const float NUM_FLT_INF = std::numeric_limits<float>::max();
+const float NUM_FLT_MIN = std::numeric_limits<float>::min();
+
+// inline function for validation check
+inline void check(
+    bool x, const char *expr, const char *file, int line, const char *err) {
+  if (!x) {
+    std::cout << "[" << file << ":" << line << "] ";
+    LOG(FATAL) << "\"" << expr << "\" check failed. " << err;
+  }
+}
+
+#define VALID_CHECK(x, info) \
+  check(static_cast<bool>(x), #x, __FILE__, __LINE__, info)
+#define VALID_CHECK_EQ(x, y, info) VALID_CHECK((x) == (y), info)
+#define VALID_CHECK_GT(x, y, info) VALID_CHECK((x) > (y), info)
+#define VALID_CHECK_LT(x, y, info) VALID_CHECK((x) < (y), info)
+
+
+// Function template for comparing two pairs
+template <typename T1, typename T2>
+bool pair_comp_first_rev(const std::pair<T1, T2> &a,
+                         const std::pair<T1, T2> &b) {
+  return a.first > b.first;
+}
+
+// Function template for comparing two pairs
+template <typename T1, typename T2>
+bool pair_comp_second_rev(const std::pair<T1, T2> &a,
+                          const std::pair<T1, T2> &b) {
+  return a.second > b.second;
+}
+
+// Return the sum of two probabilities in log scale
+template <typename T>
+T log_sum_exp(const T &x, const T &y) {
+  static T num_min = -std::numeric_limits<T>::max();
+  if (x <= num_min) return y;
+  if (y <= num_min) return x;
+  T xmax = std::max(x, y);
+  return std::log(std::exp(x - xmax) + std::exp(y - xmax)) + xmax;
+}
+
+// Get pruned probability vector for each time step's beam search
+std::vector<std::pair<size_t, float>> get_pruned_log_probs(
+    const std::vector<double> &prob_step,
+    double cutoff_prob,
+    size_t cutoff_top_n);
+
+// Get beam search result from prefixes in trie tree
+std::vector<std::pair<double, std::string>> get_beam_search_result(
+    const std::vector<PathTrie *> &prefixes,
+    const std::vector<std::string> &vocabulary,
+    size_t beam_size);
+
+// Functor for prefix comparsion
+bool prefix_compare(const PathTrie *x, const PathTrie *y);
+
+/* Get length of utf8 encoding string
+ * See: http://stackoverflow.com/a/4063229
+ */
+size_t get_utf8_str_len(const std::string &str);
+
+/* Split a string into a list of strings on a given string
+ * delimiter. NB: delimiters on beginning / end of string are
+ * trimmed. Eg, "FooBarFoo" split on "Foo" returns ["Bar"].
+ */
+std::vector<std::string> split_str(const std::string &s,
+                                   const std::string &delim);
+
+/* Splits string into vector of strings representing
+ * UTF-8 characters (not same as chars)
+ */
+std::vector<std::string> split_utf8_str(const std::string &str);
+
+// Add a word in index to the dicionary of fst
+void add_word_to_fst(const std::vector<int> &word,
+                     fst::StdVectorFst *dictionary);
+
+// Add a word in string to dictionary
+bool add_word_to_dictionary(
+    const std::string &word,
+    const std::unordered_map<std::string, int> &char_map,
+    bool add_space,
+    int SPACE_ID,
+    fst::StdVectorFst *dictionary);
+#endif  // DECODER_UTILS_H

decoders/swig/decoders.i

+%module swig_decoders
+%{
+#include "scorer.h"
+#include "ctc_greedy_decoder.h"
+#include "ctc_beam_search_decoder.h"
+#include "decoder_utils.h"
+%}
+
+%include "std_vector.i"
+%include "std_pair.i"
+%include "std_string.i"
+%import "decoder_utils.h"
+
+namespace std {
+    %template(DoubleVector) std::vector<double>;
+    %template(IntVector) std::vector<int>;
+    %template(StringVector) std::vector<std::string>;
+    %template(VectorOfStructVector) std::vector<std::vector<double> >;
+    %template(FloatVector) std::vector<float>;
+    %template(Pair) std::pair<float, std::string>;
+    %template(PairFloatStringVector)  std::vector<std::pair<float, std::string> >;
+    %template(PairDoubleStringVector) std::vector<std::pair<double, std::string> >;
+    %template(PairDoubleStringVector2) std::vector<std::vector<std::pair<double, std::string> > >;
+    %template(DoubleVector3) std::vector<std::vector<std::vector<double> > >;
+}
+
+%template(IntDoublePairCompSecondRev) pair_comp_second_rev<int, double>;
+%template(StringDoublePairCompSecondRev) pair_comp_second_rev<std::string, double>;
+%template(DoubleStringPairCompFirstRev) pair_comp_first_rev<double, std::string>;
+
+%include "scorer.h"
+%include "ctc_greedy_decoder.h"
+%include "ctc_beam_search_decoder.h"

decoders/swig/path_trie.cpp

+#include "path_trie.h"
+
+#include <algorithm>
+#include <limits>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "decoder_utils.h"
+
+PathTrie::PathTrie() {
+  log_prob_b_prev = -NUM_FLT_INF;
+  log_prob_nb_prev = -NUM_FLT_INF;
+  log_prob_b_cur = -NUM_FLT_INF;
+  log_prob_nb_cur = -NUM_FLT_INF;
+  score = -NUM_FLT_INF;
+
+  ROOT_ = -1;
+  character = ROOT_;
+  exists_ = true;
+  parent = nullptr;
+
+  dictionary_ = nullptr;
+  dictionary_state_ = 0;
+  has_dictionary_ = false;
+
+  matcher_ = nullptr;
+}
+
+PathTrie::~PathTrie() {
+  for (auto child : children_) {
+    delete child.second;
+  }
+}
+
+PathTrie* PathTrie::get_path_trie(int new_char, bool reset) {
+  auto child = children_.begin();
+  for (child = children_.begin(); child != children_.end(); ++child) {
+    if (child->first == new_char) {
+      break;
+    }
+  }
+  if (child != children_.end()) {
+    if (!child->second->exists_) {
+      child->second->exists_ = true;
+      child->second->log_prob_b_prev = -NUM_FLT_INF;
+      child->second->log_prob_nb_prev = -NUM_FLT_INF;
+      child->second->log_prob_b_cur = -NUM_FLT_INF;
+      child->second->log_prob_nb_cur = -NUM_FLT_INF;
+    }
+    return (child->second);
+  } else {
+    if (has_dictionary_) {
+      matcher_->SetState(dictionary_state_);
+      bool found = matcher_->Find(new_char);
+      if (!found) {
+        // Adding this character causes word outside dictionary
+        auto FSTZERO = fst::TropicalWeight::Zero();
+        auto final_weight = dictionary_->Final(dictionary_state_);
+        bool is_final = (final_weight != FSTZERO);
+        if (is_final && reset) {
+          dictionary_state_ = dictionary_->Start();
+        }
+        return nullptr;
+      } else {
+        PathTrie* new_path = new PathTrie;
+        new_path->character = new_char;
+        new_path->parent = this;
+        new_path->dictionary_ = dictionary_;
+        new_path->dictionary_state_ = matcher_->Value().nextstate;
+        new_path->has_dictionary_ = true;
+        new_path->matcher_ = matcher_;
+        children_.push_back(std::make_pair(new_char, new_path));
+        return new_path;
+      }
+    } else {
+      PathTrie* new_path = new PathTrie;
+      new_path->character = new_char;
+      new_path->parent = this;
+      children_.push_back(std::make_pair(new_char, new_path));
+      return new_path;
+    }
+  }
+}
+
+PathTrie* PathTrie::get_path_vec(std::vector<int>& output) {
+  return get_path_vec(output, ROOT_);
+}
+
+PathTrie* PathTrie::get_path_vec(std::vector<int>& output,
+                                 int stop,
+                                 size_t max_steps) {
+  if (character == stop || character == ROOT_ || output.size() == max_steps) {
+    std::reverse(output.begin(), output.end());
+    return this;
+  } else {
+    output.push_back(character);
+    return parent->get_path_vec(output, stop, max_steps);
+  }
+}
+
+void PathTrie::iterate_to_vec(std::vector<PathTrie*>& output) {
+  if (exists_) {
+    log_prob_b_prev = log_prob_b_cur;
+    log_prob_nb_prev = log_prob_nb_cur;
+
+    log_prob_b_cur = -NUM_FLT_INF;
+    log_prob_nb_cur = -NUM_FLT_INF;
+
+    score = log_sum_exp(log_prob_b_prev, log_prob_nb_prev);
+    output.push_back(this);
+  }
+  for (auto child : children_) {
+    child.second->iterate_to_vec(output);
+  }
+}
+
+void PathTrie::remove() {
+  exists_ = false;
+
+  if (children_.size() == 0) {
+    auto child = parent->children_.begin();
+    for (child = parent->children_.begin(); child != parent->children_.end();
+         ++child) {
+      if (child->first == character) {
+        parent->children_.erase(child);
+        break;
+      }
+    }
+
+    if (parent->children_.size() == 0 && !parent->exists_) {
+      parent->remove();
+    }
+
+    delete this;
+  }
+}
+
+void PathTrie::set_dictionary(fst::StdVectorFst* dictionary) {
+  dictionary_ = dictionary;
+  dictionary_state_ = dictionary->Start();
+  has_dictionary_ = true;
+}
+
+using FSTMATCH = fst::SortedMatcher<fst::StdVectorFst>;
+void PathTrie::set_matcher(std::shared_ptr<FSTMATCH> matcher) {
+  matcher_ = matcher;
+}

decoders/swig/path_trie.h

+#ifndef PATH_TRIE_H
+#define PATH_TRIE_H
+
+#include <algorithm>
+#include <limits>
+#include <memory>
+#include <utility>
+#include <vector>
+
+#include "fst/fstlib.h"
+
+/* Trie tree for prefix storing and manipulating, with a dictionary in
+ * finite-state transducer for spelling correction.
+ */
+class PathTrie {
+public:
+  PathTrie();
+  ~PathTrie();
+
+  // get new prefix after appending new char
+  PathTrie* get_path_trie(int new_char, bool reset = true);
+
+  // get the prefix in index from root to current node
+  PathTrie* get_path_vec(std::vector<int>& output);
+
+  // get the prefix in index from some stop node to current nodel
+  PathTrie* get_path_vec(std::vector<int>& output,
+                         int stop,
+                         size_t max_steps = std::numeric_limits<size_t>::max());
+
+  // update log probs
+  void iterate_to_vec(std::vector<PathTrie*>& output);
+
+  // set dictionary for FST
+  void set_dictionary(fst::StdVectorFst* dictionary);
+
+  void set_matcher(std::shared_ptr<fst::SortedMatcher<fst::StdVectorFst>>);
+
+  bool is_empty() { return ROOT_ == character; }
+
+  // remove current path from root
+  void remove();
+
+  float log_prob_b_prev;
+  float log_prob_nb_prev;
+  float log_prob_b_cur;
+  float log_prob_nb_cur;
+  float score;
+  float approx_ctc;
+  int character;
+  PathTrie* parent;
+
+private:
+  int ROOT_;
+  bool exists_;
+  bool has_dictionary_;
+
+  std::vector<std::pair<int, PathTrie*>> children_;
+
+  // pointer to dictionary of FST
+  fst::StdVectorFst* dictionary_;
+  fst::StdVectorFst::StateId dictionary_state_;
+  // true if finding ars in FST
+  std::shared_ptr<fst::SortedMatcher<fst::StdVectorFst>> matcher_;
+};
+
+#endif  // PATH_TRIE_H

decoders/swig/scorer.cpp

+#include "scorer.h"
+
+#include <unistd.h>
+#include <iostream>
+
+#include "lm/config.hh"
+#include "lm/model.hh"
+#include "lm/state.hh"
+#include "util/string_piece.hh"
+#include "util/tokenize_piece.hh"
+
+#include "decoder_utils.h"
+
+using namespace lm::ngram;
+
+Scorer::Scorer(double alpha,
+               double beta,
+               const std::string& lm_path,
+               const std::vector<std::string>& vocab_list) {
+  this->alpha = alpha;
+  this->beta = beta;
+
+  dictionary = nullptr;
+  is_character_based_ = true;
+  language_model_ = nullptr;
+
+  max_order_ = 0;
+  dict_size_ = 0;
+  SPACE_ID_ = -1;
+
+  setup(lm_path, vocab_list);
+}
+
+Scorer::~Scorer() {
+  if (language_model_ != nullptr) {
+    delete static_cast<lm::base::Model*>(language_model_);
+  }
+  if (dictionary != nullptr) {
+    delete static_cast<fst::StdVectorFst*>(dictionary);
+  }
+}
+
+void Scorer::setup(const std::string& lm_path,
+                   const std::vector<std::string>& vocab_list) {
+  // load language model
+  load_lm(lm_path);
+  // set char map for scorer
+  set_char_map(vocab_list);
+  // fill the dictionary for FST
+  if (!is_character_based()) {
+    fill_dictionary(true);
+  }
+}
+
+void Scorer::load_lm(const std::string& lm_path) {
+  const char* filename = lm_path.c_str();
+  VALID_CHECK_EQ(access(filename, F_OK), 0, "Invalid language model path");
+
+  RetriveStrEnumerateVocab enumerate;
+  lm::ngram::Config config;
+  config.enumerate_vocab = &enumerate;
+  language_model_ = lm::ngram::LoadVirtual(filename, config);
+  max_order_ = static_cast<lm::base::Model*>(language_model_)->Order();
+  vocabulary_ = enumerate.vocabulary;
+  for (size_t i = 0; i < vocabulary_.size(); ++i) {
+    if (is_character_based_ && vocabulary_[i] != UNK_TOKEN &&
+        vocabulary_[i] != START_TOKEN && vocabulary_[i] != END_TOKEN &&
+        get_utf8_str_len(enumerate.vocabulary[i]) > 1) {
+      is_character_based_ = false;
+    }
+  }
+}
+
+double Scorer::get_log_cond_prob(const std::vector<std::string>& words) {
+  lm::base::Model* model = static_cast<lm::base::Model*>(language_model_);
+  double cond_prob;
+  lm::ngram::State state, tmp_state, out_state;
+  // avoid to inserting <s> in begin
+  model->NullContextWrite(&state);
+  for (size_t i = 0; i < words.size(); ++i) {
+    lm::WordIndex word_index = model->BaseVocabulary().Index(words[i]);
+    // encounter OOV
+    if (word_index == 0) {
+      return OOV_SCORE;
+    }
+    cond_prob = model->BaseScore(&state, word_index, &out_state);
+    tmp_state = state;
+    state = out_state;
+    out_state = tmp_state;
+  }
+  // return  log10 prob
+  return cond_prob;
+}
+
+double Scorer::get_sent_log_prob(const std::vector<std::string>& words) {
+  std::vector<std::string> sentence;
+  if (words.size() == 0) {
+    for (size_t i = 0; i < max_order_; ++i) {
+      sentence.push_back(START_TOKEN);
+    }
+  } else {
+    for (size_t i = 0; i < max_order_ - 1; ++i) {
+      sentence.push_back(START_TOKEN);
+    }
+    sentence.insert(sentence.end(), words.begin(), words.end());
+  }
+  sentence.push_back(END_TOKEN);
+  return get_log_prob(sentence);
+}
+
+double Scorer::get_log_prob(const std::vector<std::string>& words) {
+  assert(words.size() > max_order_);
+  double score = 0.0;
+  for (size_t i = 0; i < words.size() - max_order_ + 1; ++i) {
+    std::vector<std::string> ngram(words.begin() + i,
+                                   words.begin() + i + max_order_);
+    score += get_log_cond_prob(ngram);
+  }
+  return score;
+}
+
+void Scorer::reset_params(float alpha, float beta) {
+  this->alpha = alpha;
+  this->beta = beta;
+}
+
+std::string Scorer::vec2str(const std::vector<int>& input) {
+  std::string word;
+  for (auto ind : input) {
+    word += char_list_[ind];
+  }
+  return word;
+}
+
+std::vector<std::string> Scorer::split_labels(const std::vector<int>& labels) {
+  if (labels.empty()) return {};
+
+  std::string s = vec2str(labels);
+  std::vector<std::string> words;
+  if (is_character_based_) {
+    words = split_utf8_str(s);
+  } else {
+    words = split_str(s, " ");
+  }
+  return words;
+}
+
+void Scorer::set_char_map(const std::vector<std::string>& char_list) {
+  char_list_ = char_list;
+  char_map_.clear();
+
+  for (size_t i = 0; i < char_list_.size(); i++) {
+    if (char_list_[i] == " ") {
+      SPACE_ID_ = i;
+      char_map_[' '] = i;
+    } else if (char_list_[i].size() == 1) {
+      char_map_[char_list_[i][0]] = i;
+    }
+  }
+}
+
+std::vector<std::string> Scorer::make_ngram(PathTrie* prefix) {
+  std::vector<std::string> ngram;
+  PathTrie* current_node = prefix;
+  PathTrie* new_node = nullptr;
+
+  for (int order = 0; order < max_order_; order++) {
+    std::vector<int> prefix_vec;
+
+    if (is_character_based_) {
+      new_node = current_node->get_path_vec(prefix_vec, SPACE_ID_, 1);
+      current_node = new_node;
+    } else {
+      new_node = current_node->get_path_vec(prefix_vec, SPACE_ID_);
+      current_node = new_node->parent;  // Skipping spaces
+    }
+
+    // reconstruct word
+    std::string word = vec2str(prefix_vec);
+    ngram.push_back(word);
+
+    if (new_node->character == -1) {
+      // No more spaces, but still need order
+      for (int i = 0; i < max_order_ - order - 1; i++) {
+        ngram.push_back(START_TOKEN);
+      }
+      break;
+    }
+  }
+  std::reverse(ngram.begin(), ngram.end());
+  return ngram;
+}
+
+void Scorer::fill_dictionary(bool add_space) {
+  fst::StdVectorFst dictionary;
+  // First reverse char_list so ints can be accessed by chars
+  std::unordered_map<std::string, int> char_map;
+  for (size_t i = 0; i < char_list_.size(); i++) {
+    char_map[char_list_[i]] = i;
+  }
+
+  // For each unigram convert to ints and put in trie
+  int dict_size = 0;
+  for (const auto& word : vocabulary_) {
+    bool added = add_word_to_dictionary(
+        word, char_map, add_space, SPACE_ID_, &dictionary);
+    dict_size += added ? 1 : 0;
+  }
+
+  dict_size_ = dict_size;
+
+  /* Simplify FST
+
+   * This gets rid of "epsilon" transitions in the FST.
+   * These are transitions that don't require a string input to be taken.
+   * Getting rid of them is necessary to make the FST determinisitc, but
+   * can greatly increase the size of the FST
+   */
+  fst::RmEpsilon(&dictionary);
+  fst::StdVectorFst* new_dict = new fst::StdVectorFst;
+
+  /* This makes the FST deterministic, meaning for any string input there's
+   * only one possible state the FST could be in.  It is assumed our
+   * dictionary is deterministic when using it.
+   * (lest we'd have to check for multiple transitions at each state)
+   */
+  fst::Determinize(dictionary, new_dict);
+
+  /* Finds the simplest equivalent fst. This is unnecessary but decreases
+   * memory usage of the dictionary
+   */
+  fst::Minimize(new_dict);
+  this->dictionary = new_dict;
+}

decoders/swig/scorer.h

+#ifndef SCORER_H_
+#define SCORER_H_
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "lm/enumerate_vocab.hh"
+#include "lm/virtual_interface.hh"
+#include "lm/word_index.hh"
+#include "util/string_piece.hh"
+
+#include "path_trie.h"
+
+const double OOV_SCORE = -1000.0;
+const std::string START_TOKEN = "<s>";
+const std::string UNK_TOKEN = "<unk>";
+const std::string END_TOKEN = "</s>";
+
+// Implement a callback to retrive the dictionary of language model.
+class RetriveStrEnumerateVocab : public lm::EnumerateVocab {
+public:
+  RetriveStrEnumerateVocab() {}
+
+  void Add(lm::WordIndex index, const StringPiece &str) {
+    vocabulary.push_back(std::string(str.data(), str.length()));
+  }
+
+  std::vector<std::string> vocabulary;
+};
+
+/* External scorer to query score for n-gram or sentence, including language
+ * model scoring and word insertion.
+ *
+ * Example:
+ *     Scorer scorer(alpha, beta, "path_of_language_model");
+ *     scorer.get_log_cond_prob({ "WORD1", "WORD2", "WORD3" });
+ *     scorer.get_sent_log_prob({ "WORD1", "WORD2", "WORD3" });
+ */
+class Scorer {
+public:
+  Scorer(double alpha,
+         double beta,
+         const std::string &lm_path,
+         const std::vector<std::string> &vocabulary);
+  ~Scorer();
+
+  double get_log_cond_prob(const std::vector<std::string> &words);
+
+  double get_sent_log_prob(const std::vector<std::string> &words);
+
+  // return the max order
+  size_t get_max_order() const { return max_order_; }
+
+  // return the dictionary size of language model
+  size_t get_dict_size() const { return dict_size_; }
+
+  // retrun true if the language model is character based
+  bool is_character_based() const { return is_character_based_; }
+
+  // reset params alpha & beta
+  void reset_params(float alpha, float beta);
+
+  // make ngram for a given prefix
+  std::vector<std::string> make_ngram(PathTrie *prefix);
+
+  // trransform the labels in index to the vector of words (word based lm) or
+  // the vector of characters (character based lm)
+  std::vector<std::string> split_labels(const std::vector<int> &labels);
+
+  // language model weight
+  double alpha;
+  // word insertion weight
+  double beta;
+
+  // pointer to the dictionary of FST
+  void *dictionary;
+
+protected:
+  // necessary setup: load language model, set char map, fill FST's dictionary
+  void setup(const std::string &lm_path,
+             const std::vector<std::string> &vocab_list);
+
+  // load language model from given path
+  void load_lm(const std::string &lm_path);
+
+  // fill dictionary for FST
+  void fill_dictionary(bool add_space);
+
+  // set char map
+  void set_char_map(const std::vector<std::string> &char_list);
+
+  double get_log_prob(const std::vector<std::string> &words);
+
+  // translate the vector in index to string
+  std::string vec2str(const std::vector<int> &input);
+
+private:
+  void *language_model_;
+  bool is_character_based_;
+  size_t max_order_;
+  size_t dict_size_;
+
+  int SPACE_ID_;
+  std::vector<std::string> char_list_;
+  std::unordered_map<char, int> char_map_;
+
+  std::vector<std::string> vocabulary_;
+};
+
+#endif  // SCORER_H_

decoders/swig/setup.py

+"""Script to build and install decoder package."""
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+from setuptools import setup, Extension, distutils
+import glob
+import platform
+import os, sys
+import multiprocessing.pool
+import argparse
+
+parser = argparse.ArgumentParser(description=__doc__)
+parser.add_argument(
+    "--num_processes",
+    default=1,
+    type=int,
+    help="Number of cpu processes to build package. (default: %(default)d)")
+args = parser.parse_known_args()
+
+# reconstruct sys.argv to pass to setup below
+sys.argv = [sys.argv[0]] + args[1]
+
+
+# monkey-patch for parallel compilation
+# See: https://stackoverflow.com/a/13176803
+def parallelCCompile(self,
+                     sources,
+                     output_dir=None,
+                     macros=None,
+                     include_dirs=None,
+                     debug=0,
+                     extra_preargs=None,
+                     extra_postargs=None,
+                     depends=None):
+    # those lines are copied from distutils.ccompiler.CCompiler directly
+    macros, objects, extra_postargs, pp_opts, build = self._setup_compile(
+        output_dir, macros, include_dirs, sources, depends, extra_postargs)
+    cc_args = self._get_cc_args(pp_opts, debug, extra_preargs)
+
+    # parallel code
+    def _single_compile(obj):
+        try:
+            src, ext = build[obj]
+        except KeyError:
+            return
+        self._compile(obj, src, ext, cc_args, extra_postargs, pp_opts)
+
+    # convert to list, imap is evaluated on-demand
+    thread_pool = multiprocessing.pool.ThreadPool(args[0].num_processes)
+    list(thread_pool.imap(_single_compile, objects))
+    return objects
+
+
+def compile_test(header, library):
+    dummy_path = os.path.join(os.path.dirname(__file__), "dummy")
+    command = "bash -c \"g++ -include " + header \
+                + " -l" + library + " -x c++ - <<<'int main() {}' -o " \
+                + dummy_path + " >/dev/null 2>/dev/null && rm " \
+                + dummy_path + " 2>/dev/null\""
+    return os.system(command) == 0
+
+
+# hack compile to support parallel compiling
+distutils.ccompiler.CCompiler.compile = parallelCCompile
+
+FILES = glob.glob('kenlm/util/*.cc') \
+        + glob.glob('kenlm/lm/*.cc') \
+        + glob.glob('kenlm/util/double-conversion/*.cc')
+
+FILES += glob.glob('openfst-1.6.3/src/lib/*.cc')
+
+# FILES + glob.glob('glog/src/*.cc')
+FILES = [
+    fn for fn in FILES
+    if not (fn.endswith('main.cc') or fn.endswith('test.cc') or fn.endswith(
+        'unittest.cc'))
+]
+
+LIBS = ['stdc++']
+if platform.system() != 'Darwin':
+    LIBS.append('rt')
+
+ARGS = ['-O3', '-DNDEBUG', '-DKENLM_MAX_ORDER=6', '-std=c++11']
+
+if compile_test('zlib.h', 'z'):
+    ARGS.append('-DHAVE_ZLIB')
+    LIBS.append('z')
+
+if compile_test('bzlib.h', 'bz2'):
+    ARGS.append('-DHAVE_BZLIB')
+    LIBS.append('bz2')
+
+if compile_test('lzma.h', 'lzma'):
+    ARGS.append('-DHAVE_XZLIB')
+    LIBS.append('lzma')
+
+os.system('swig -python -c++ ./decoders.i')
+
+decoders_module = [
+    Extension(
+        name='_swig_decoders',
+        sources=FILES + glob.glob('*.cxx') + glob.glob('*.cpp'),
+        language='c++',
+        include_dirs=[
+            '.',
+            'kenlm',
+            'openfst-1.6.3/src/include',
+            'ThreadPool',
+            #'glog/src'
+        ],
+        libraries=LIBS,
+        extra_compile_args=ARGS)
+]
+
+setup(
+    name='swig_decoders',
+    version='0.1',
+    description="""CTC decoders""",
+    ext_modules=decoders_module,
+    py_modules=['swig_decoders'], )

decoders/swig/setup.sh

+#!/usr/bin/env bash
+
+if [ ! -d kenlm ]; then
+    git clone https://github.com/luotao1/kenlm.git
+    echo -e "\n"
+fi
+
+if [ ! -d openfst-1.6.3 ]; then
+    echo "Download and extract openfst ..."
+    wget http://www.openfst.org/twiki/pub/FST/FstDownload/openfst-1.6.3.tar.gz
+    tar -xzvf openfst-1.6.3.tar.gz
+    echo -e "\n"
+fi
+
+if [ ! -d ThreadPool ]; then
+    git clone https://github.com/progschj/ThreadPool.git
+    echo -e "\n"
+fi
+
+echo "Install decoders ..."
+python setup.py install --num_processes 4

decoders/swig_wrapper.py

+"""Wrapper for various CTC decoders in SWIG."""
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import swig_decoders
+
+
+class Scorer(swig_decoders.Scorer):
+    """Wrapper for Scorer.
+
+    :param alpha: Parameter associated with language model. Don't use
+                  language model when alpha = 0.
+    :type alpha: float
+    :param beta: Parameter associated with word count. Don't use word
+                 count when beta = 0.
+    :type beta: float
+    :model_path: Path to load language model.
+    :type model_path: basestring
+    """
+
+    def __init__(self, alpha, beta, model_path, vocabulary):
+        swig_decoders.Scorer.__init__(self, alpha, beta, model_path, vocabulary)
+
+
+def ctc_greedy_decoder(probs_seq, vocabulary):
+    """Wrapper for ctc best path decoder in swig.
+
+    :param probs_seq: 2-D list of probability distributions over each time
+                      step, with each element being a list of normalized
+                      probabilities over vocabulary and blank.
+    :type probs_seq: 2-D list
+    :param vocabulary: Vocabulary list.
+    :type vocabulary: list
+    :return: Decoding result string.
+    :rtype: basestring
+    """
+    return swig_decoders.ctc_greedy_decoder(probs_seq.tolist(), vocabulary)
+
+
+def ctc_beam_search_decoder(probs_seq,
+                            vocabulary,
+                            beam_size,
+                            cutoff_prob=1.0,
+                            cutoff_top_n=40,
+                            ext_scoring_func=None):
+    """Wrapper for the CTC Beam Search Decoder.
+
+    :param probs_seq: 2-D list of probability distributions over each time
+                      step, with each element being a list of normalized
+                      probabilities over vocabulary and blank.
+    :type probs_seq: 2-D list
+    :param vocabulary: Vocabulary list.
+    :type vocabulary: list
+    :param beam_size: Width for beam search.
+    :type beam_size: int
+    :param cutoff_prob: Cutoff probability in pruning,
+                        default 1.0, no pruning.
+    :type cutoff_prob: float
+    :param cutoff_top_n: Cutoff number in pruning, only top cutoff_top_n
+                         characters with highest probs in vocabulary will be
+                         used in beam search, default 40.
+    :type cutoff_top_n: int
+    :param ext_scoring_func: External scoring function for
+                             partially decoded sentence, e.g. word count
+                             or language model.
+    :type external_scoring_func: callable
+    :return: List of tuples of log probability and sentence as decoding
+             results, in descending order of the probability.
+    :rtype: list
+    """
+    return swig_decoders.ctc_beam_search_decoder(probs_seq.tolist(), vocabulary,
+                                                 beam_size, cutoff_prob,
+                                                 cutoff_top_n, ext_scoring_func)
+
+
+def ctc_beam_search_decoder_batch(probs_split,
+                                  vocabulary,
+                                  beam_size,
+                                  num_processes,
+                                  cutoff_prob=1.0,
+                                  cutoff_top_n=40,
+                                  ext_scoring_func=None):
+    """Wrapper for the batched CTC beam search decoder.
+
+    :param probs_seq: 3-D list with each element as an instance of 2-D list
+                      of probabilities used by ctc_beam_search_decoder().
+    :type probs_seq: 3-D list
+    :param vocabulary: Vocabulary list.
+    :type vocabulary: list
+    :param beam_size: Width for beam search.
+    :type beam_size: int
+    :param num_processes: Number of parallel processes.
+    :type num_processes: int
+    :param cutoff_prob: Cutoff probability in vocabulary pruning,
+                        default 1.0, no pruning.
+    :type cutoff_prob: float
+    :param cutoff_top_n: Cutoff number in pruning, only top cutoff_top_n
+                         characters with highest probs in vocabulary will be
+                         used in beam search, default 40.
+    :type cutoff_top_n: int
+    :param num_processes: Number of parallel processes.
+    :type num_processes: int
+    :param ext_scoring_func: External scoring function for
+                             partially decoded sentence, e.g. word count
+                             or language model.
+    :type external_scoring_function: callable
+    :return: List of tuples of log probability and sentence as decoding
+             results, in descending order of the probability.
+    :rtype: list
+    """
+    probs_split = [probs_seq.tolist() for probs_seq in probs_split]
+
+    return swig_decoders.ctc_beam_search_decoder_batch(
+        probs_split, vocabulary, beam_size, num_processes, cutoff_prob,
+        cutoff_top_n, ext_scoring_func)

model_utils/tests/test_decoders.py → decoders/tests/test_decoders.py

@@ -4,7 +4,7 @@ from __future__ import division
 from __future__ import print_function
 
 import unittest
-from model_utils import decoder
+from decoders import decoders_deprecated as decoder
 
 
 class TestDecoders(unittest.TestCase):
@@ -66,16 +66,14 @@ class TestDecoders(unittest.TestCase):
         beam_result = decoder.ctc_beam_search_decoder(
             probs_seq=self.probs_seq1,
             beam_size=self.beam_size,
-            vocabulary=self.vocab_list,
-            blank_id=len(self.vocab_list))
+            vocabulary=self.vocab_list)
         self.assertEqual(beam_result[0][1], self.beam_search_result[0])
 
     def test_beam_search_decoder_2(self):
         beam_result = decoder.ctc_beam_search_decoder(
             probs_seq=self.probs_seq2,
             beam_size=self.beam_size,
-            vocabulary=self.vocab_list,
-            blank_id=len(self.vocab_list))
+            vocabulary=self.vocab_list)
         self.assertEqual(beam_result[0][1], self.beam_search_result[1])
 
     def test_beam_search_decoder_batch(self):
@@ -83,7 +81,6 @@ class TestDecoders(unittest.TestCase):
             probs_split=[self.probs_seq1, self.probs_seq2],
             beam_size=self.beam_size,
             vocabulary=self.vocab_list,
-            blank_id=len(self.vocab_list),
             num_processes=24)
         self.assertEqual(beam_results[0][0][1], self.beam_search_result[0])
         self.assertEqual(beam_results[1][0][1], self.beam_search_result[1])

examples/librispeech/run_infer.sh

@@ -21,9 +21,10 @@ python -u infer.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
+--cutoff_top_n=40 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/librispeech/run_infer_golden.sh

@@ -30,9 +30,10 @@ python -u infer.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
+--cutoff_top_n=40 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/librispeech/run_test.sh

@@ -22,9 +22,9 @@ python -u test.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/librispeech/run_test_golden.sh

@@ -31,9 +31,10 @@ python -u test.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
+--cutoff_top_n=40 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/tiny/run_infer.sh

@@ -21,9 +21,9 @@ python -u infer.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/tiny/run_infer_golden.sh

@@ -30,9 +30,9 @@ python -u infer.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/tiny/run_test.sh

@@ -22,9 +22,9 @@ python -u test.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

examples/tiny/run_test_golden.sh

@@ -31,9 +31,9 @@ python -u test.py \
 --num_conv_layers=2 \
 --num_rnn_layers=3 \
 --rnn_layer_size=2048 \
---alpha=0.36 \
---beta=0.25 \
---cutoff_prob=0.99 \
+--alpha=2.15 \
+--beta=0.35 \
+--cutoff_prob=1.0 \
 --use_gru=False \
 --use_gpu=True \
 --share_rnn_weights=True \

infer.py

@@ -21,9 +21,10 @@ add_arg('num_proc_bsearch', int,    12,     "# of CPUs for beam search.")
 add_arg('num_conv_layers',  int,    2,      "# of convolution layers.")
 add_arg('num_rnn_layers',   int,    3,      "# of recurrent layers.")
 add_arg('rnn_layer_size',   int,    2048,   "# of recurrent cells per layer.")
-add_arg('alpha',            float,  0.36,   "Coef of LM for beam search.")
-add_arg('beta',             float,  0.25,   "Coef of WC for beam search.")
-add_arg('cutoff_prob',      float,  0.99,   "Cutoff probability for pruning.")
+add_arg('alpha',            float,  2.15,   "Coef of LM for beam search.")
+add_arg('beta',             float,  0.35,   "Coef of WC for beam search.")
+add_arg('cutoff_prob',      float,  1.0,    "Cutoff probability for pruning.")
+add_arg('cutoff_top_n',     int,    40,     "Cutoff number for pruning.")
 add_arg('use_gru',          bool,   False,  "Use GRUs instead of simple RNNs.")
 add_arg('use_gpu',          bool,   True,   "Use GPU or not.")
 add_arg('share_rnn_weights',bool,   True,   "Share input-hidden weights across "
@@ -84,6 +85,10 @@ def infer():
         use_gru=args.use_gru,
         pretrained_model_path=args.model_path,
         share_rnn_weights=args.share_rnn_weights)
+
+    # decoders only accept string encoded in utf-8
+    vocab_list = [chars.encode("utf-8") for chars in data_generator.vocab_list]
+
     result_transcripts = ds2_model.infer_batch(
         infer_data=infer_data,
         decoding_method=args.decoding_method,
@@ -91,7 +96,8 @@ def infer():
         beam_beta=args.beta,
         beam_size=args.beam_size,
         cutoff_prob=args.cutoff_prob,
-        vocab_list=data_generator.vocab_list,
+        cutoff_top_n=args.cutoff_top_n,
+        vocab_list=vocab_list,
         language_model_path=args.lang_model_path,
         num_processes=args.num_proc_bsearch)
 
@@ -106,6 +112,7 @@ def infer():
         print("Current error rate [%s] = %f" %
               (args.error_rate_type, error_rate_func(target, result)))
 
+    ds2_model.logger.info("finish inference")
 
 def main():
     print_arguments(args)

model_utils/model.py

@@ -6,14 +6,18 @@ from __future__ import print_function
 import sys
 import os
 import time
+import logging
 import gzip
 from distutils.dir_util import mkpath
 import paddle.v2 as paddle
-from model_utils.lm_scorer import LmScorer
-from model_utils.decoder import ctc_greedy_decoder, ctc_beam_search_decoder
-from model_utils.decoder import ctc_beam_search_decoder_batch
+from decoders.swig_wrapper import Scorer
+from decoders.swig_wrapper import ctc_greedy_decoder
+from decoders.swig_wrapper import ctc_beam_search_decoder_batch
 from model_utils.network import deep_speech_v2_network
 
+logging.basicConfig(
+    format='[%(levelname)s %(asctime)s %(filename)s:%(lineno)d] %(message)s')
+
 
 class DeepSpeech2Model(object):
     """DeepSpeech2Model class.
@@ -44,6 +48,8 @@ class DeepSpeech2Model(object):
         self._inferer = None
         self._loss_inferer = None
         self._ext_scorer = None
+        self.logger = logging.getLogger("")
+        self.logger.setLevel(level=logging.INFO)
 
     def train(self,
               train_batch_reader,
@@ -157,8 +163,8 @@ class DeepSpeech2Model(object):
         return self._loss_inferer.infer(input=infer_data)
 
     def infer_batch(self, infer_data, decoding_method, beam_alpha, beam_beta,
-                    beam_size, cutoff_prob, vocab_list, language_model_path,
-                    num_processes):
+                    beam_size, cutoff_prob, cutoff_top_n, vocab_list,
+                    language_model_path, num_processes):
         """Model inference. Infer the transcription for a batch of speech
         utterances.
 
@@ -178,6 +184,10 @@ class DeepSpeech2Model(object):
         :param cutoff_prob: Cutoff probability in pruning,
                             default 1.0, no pruning.
         :type cutoff_prob: float
+        :param cutoff_top_n: Cutoff number in pruning, only top cutoff_top_n
+                        characters with highest probs in vocabulary will be
+                        used in beam search, default 40.
+        :type cutoff_top_n: int
         :param vocab_list: List of tokens in the vocabulary, for decoding.
         :type vocab_list: list
         :param language_model_path: Filepath for language model.
@@ -209,21 +219,33 @@ class DeepSpeech2Model(object):
         elif decoding_method == "ctc_beam_search":
             # initialize external scorer
             if self._ext_scorer == None:
-                self._ext_scorer = LmScorer(beam_alpha, beam_beta,
-                                            language_model_path)
                 self._loaded_lm_path = language_model_path
+                self.logger.info("begin to initialize the external scorer "
+                                 "for decoding")
+                self._ext_scorer = Scorer(beam_alpha, beam_beta,
+                                          language_model_path, vocab_list)
+
+                lm_char_based = self._ext_scorer.is_character_based()
+                lm_max_order = self._ext_scorer.get_max_order()
+                lm_dict_size = self._ext_scorer.get_dict_size()
+                self.logger.info("language model: "
+                                 "is_character_based = %d," % lm_char_based +
+                                 " max_order = %d," % lm_max_order +
+                                 " dict_size = %d" % lm_dict_size)
+                self.logger.info("end initializing scorer. Start decoding ...")
             else:
                 self._ext_scorer.reset_params(beam_alpha, beam_beta)
                 assert self._loaded_lm_path == language_model_path
             # beam search decode
+            num_processes = min(num_processes, len(probs_split))
             beam_search_results = ctc_beam_search_decoder_batch(
                 probs_split=probs_split,
                 vocabulary=vocab_list,
                 beam_size=beam_size,
-                blank_id=len(vocab_list),
                 num_processes=num_processes,
                 ext_scoring_func=self._ext_scorer,
-                cutoff_prob=cutoff_prob)
+                cutoff_prob=cutoff_prob,
+                cutoff_top_n=cutoff_top_n)
 
             results = [result[0][1] for result in beam_search_results]
         else:

requirements.txt

@@ -2,4 +2,3 @@ scipy==0.13.1
 resampy==0.1.5
 SoundFile==0.9.0.post1
 python_speech_features
-https://github.com/luotao1/kenlm/archive/master.zip

setup.sh

-#! /usr/bin/env bash
+#! /usr/bin/env  bash
 
 # install python dependencies
 if [ -f "requirements.txt" ]; then
@@ -20,10 +20,19 @@ if [ $? != 0 ]; then
     fi
     tar -zxvf libsndfile-1.0.28.tar.gz
     cd libsndfile-1.0.28
-    ./configure && make && make install
+    ./configure > /dev/null && make > /dev/null && make install > /dev/null
     cd ..
     rm -rf libsndfile-1.0.28
     rm libsndfile-1.0.28.tar.gz
 fi
 
+# install decoders
+python -c "import swig_decoders"
+if [ $? != 0 ]; then
+    cd decoders/swig > /dev/null
+    sh setup.sh
+    cd - > /dev/null
+fi
+
+
 echo "Install all dependencies successfully."

test.py

@@ -22,9 +22,10 @@ add_arg('num_proc_data',    int,    12,     "# of CPUs for data preprocessing.")
 add_arg('num_conv_layers',  int,    2,      "# of convolution layers.")
 add_arg('num_rnn_layers',   int,    3,      "# of recurrent layers.")
 add_arg('rnn_layer_size',   int,    2048,   "# of recurrent cells per layer.")
-add_arg('alpha',            float,  0.36,   "Coef of LM for beam search.")
-add_arg('beta',             float,  0.25,   "Coef of WC for beam search.")
-add_arg('cutoff_prob',      float,  0.99,   "Cutoff probability for pruning.")
+add_arg('alpha',            float,  2.15,   "Coef of LM for beam search.")
+add_arg('beta',             float,  0.35,   "Coef of WC for beam search.")
+add_arg('cutoff_prob',      float,  1.0,    "Cutoff probability for pruning.")
+add_arg('cutoff_top_n',     int,    40,     "Cutoff number for pruning.")
 add_arg('use_gru',          bool,   False,  "Use GRUs instead of simple RNNs.")
 add_arg('use_gpu',          bool,   True,   "Use GPU or not.")
 add_arg('share_rnn_weights',bool,   True,   "Share input-hidden weights across "
@@ -85,6 +86,9 @@ def evaluate():
         pretrained_model_path=args.model_path,
         share_rnn_weights=args.share_rnn_weights)
 
+    # decoders only accept string encoded in utf-8
+    vocab_list = [chars.encode("utf-8") for chars in data_generator.vocab_list]
+
     error_rate_func = cer if args.error_rate_type == 'cer' else wer
     error_sum, num_ins = 0.0, 0
     for infer_data in batch_reader():
@@ -95,7 +99,8 @@ def evaluate():
             beam_beta=args.beta,
             beam_size=args.beam_size,
             cutoff_prob=args.cutoff_prob,
-            vocab_list=data_generator.vocab_list,
+            cutoff_top_n=args.cutoff_top_n,
+            vocab_list=vocab_list,
             language_model_path=args.lang_model_path,
             num_processes=args.num_proc_bsearch)
         target_transcripts = [
@@ -110,6 +115,7 @@ def evaluate():
     print("Final error rate [%s] (%d/%d) = %f" %
           (args.error_rate_type, num_ins, num_ins, error_sum / num_ins))
 
+    ds2_model.logger.info("finish evaluation")
 
 def main():
     print_arguments(args)