From 921c6d0cc1d9f2595edd710db3a7770e7d392988 Mon Sep 17 00:00:00 2001
From: Yibing Liu <liuyibing01@baidu.com>
Date: Mon, 6 Nov 2017 23:20:20 +0800
Subject: [PATCH 1/2] Add the scoring of last word/char of prefixes in CTC beam
 search decoder

---
 decoders/swig/ctc_beam_search_decoder.cpp | 28 +++++++++++++++++++----
 1 file changed, 23 insertions(+), 5 deletions(-)

diff --git a/decoders/swig/ctc_beam_search_decoder.cpp b/decoders/swig/ctc_beam_search_decoder.cpp
index 624784b05..0f33e8573 100644
--- a/decoders/swig/ctc_beam_search_decoder.cpp
+++ b/decoders/swig/ctc_beam_search_decoder.cpp
@@ -110,17 +110,17 @@ std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
           // language model scoring
           if (ext_scorer != nullptr &&
               (c == space_id || ext_scorer->is_character_based())) {
-            PathTrie *prefix_toscore = nullptr;
+            PathTrie *prefix_to_score = nullptr;
             // skip scoring the space
             if (ext_scorer->is_character_based()) {
-              prefix_toscore = prefix_new;
+              prefix_to_score = prefix_new;
             } else {
-              prefix_toscore = prefix;
+              prefix_to_score = prefix;
             }
 
-            double score = 0.0;
+            float score = 0.0;
             std::vector<std::string> ngram;
-            ngram = ext_scorer->make_ngram(prefix_toscore);
+            ngram = ext_scorer->make_ngram(prefix_to_score);
             score = ext_scorer->get_log_cond_prob(ngram) * ext_scorer->alpha;
             log_p += score;
             log_p += ext_scorer->beta;
@@ -131,6 +131,7 @@ std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
       }  // end of loop over prefix
     }    // end of loop over vocabulary
 
+
     prefixes.clear();
     // update log probs
     root.iterate_to_vec(prefixes);
@@ -147,6 +148,23 @@ std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
     }
   }  // end of loop over time
 
+  // score the last word/character of each prefix
+  if (ext_scorer != nullptr) {
+    for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
+      auto prefix = prefixes[i];
+      if (prefix->character != space_id && !prefix->is_empty()) {
+        float score = 0.0;
+        std::vector<std::string> ngram = ext_scorer->make_ngram(prefix);
+        score = ext_scorer->get_log_cond_prob(ngram) * ext_scorer->alpha;
+        score += ext_scorer->beta;
+        prefix->score += score;
+      }
+    }
+  }
+
+  size_t num_prefixes = std::min(prefixes.size(), beam_size);
+  std::sort(prefixes.begin(), prefixes.begin() + num_prefixes, prefix_compare);
+
   // 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) {

From 4b20a7029c24a9645dea56682d527b8137150cd2 Mon Sep 17 00:00:00 2001
From: Yibing Liu <liuyibing01@baidu.com>
Date: Tue, 7 Nov 2017 17:10:15 +0800
Subject: [PATCH 2/2] skip scoring the end when using character-based scorer

---
 decoders/swig/ctc_beam_search_decoder.cpp | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/decoders/swig/ctc_beam_search_decoder.cpp b/decoders/swig/ctc_beam_search_decoder.cpp
index 0f33e8573..4a63af26a 100644
--- a/decoders/swig/ctc_beam_search_decoder.cpp
+++ b/decoders/swig/ctc_beam_search_decoder.cpp
@@ -148,11 +148,11 @@ std::vector<std::pair<double, std::string>> ctc_beam_search_decoder(
     }
   }  // end of loop over time
 
-  // score the last word/character of each prefix
-  if (ext_scorer != nullptr) {
+  // score the last word of each prefix that doesn't end with space
+  if (ext_scorer != nullptr && !ext_scorer->is_character_based()) {
     for (size_t i = 0; i < beam_size && i < prefixes.size(); ++i) {
       auto prefix = prefixes[i];
-      if (prefix->character != space_id && !prefix->is_empty()) {
+      if (!prefix->is_empty() && prefix->character != space_id) {
         float score = 0.0;
         std::vector<std::string> ngram = ext_scorer->make_ngram(prefix);
         score = ext_scorer->get_log_cond_prob(ngram) * ext_scorer->alpha;