From 46d833dc92d99f8cbcf5c45e4624ffaca954570b Mon Sep 17 00:00:00 2001
From: Chris Dyer <cdyer@cs.cmu.edu>
Date: Thu, 29 Dec 2011 21:09:14 -0500
Subject: ngram base dist

---
 gi/pf/ngram_base.cc | 69 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 69 insertions(+)
 create mode 100644 gi/pf/ngram_base.cc

(limited to 'gi/pf/ngram_base.cc')

diff --git a/gi/pf/ngram_base.cc b/gi/pf/ngram_base.cc
new file mode 100644
index 00000000..1299f06f
--- /dev/null
+++ b/gi/pf/ngram_base.cc
@@ -0,0 +1,69 @@
+#include "ngram_base.h"
+
+#include "lm/model.hh"
+#include "tdict.h"
+
+using namespace std;
+
+namespace {
+struct GICSVMapper : public lm::EnumerateVocab {
+  GICSVMapper(vector<lm::WordIndex>* out) : out_(out), kLM_UNKNOWN_TOKEN(0) { out_->clear(); }
+  void Add(lm::WordIndex index, const StringPiece &str) {
+    const WordID cdec_id = TD::Convert(str.as_string());
+    if (cdec_id >= out_->size())
+      out_->resize(cdec_id + 1, kLM_UNKNOWN_TOKEN);
+    (*out_)[cdec_id] = index;
+  }
+  vector<lm::WordIndex>* out_;
+  const lm::WordIndex kLM_UNKNOWN_TOKEN;
+};
+}
+
+struct FixedNgramBaseImpl {
+  FixedNgramBaseImpl(const string& param) {
+    GICSVMapper vm(&cdec2klm_map_);
+    lm::ngram::Config conf;
+    conf.enumerate_vocab = &vm;
+    cerr << "Reading character LM from " << param << endl;
+    model = new lm::ngram::ProbingModel(param.c_str(), conf);
+    order = model->Order();
+    kEOS = MapWord(TD::Convert("</s>"));
+    assert(kEOS > 0);
+  }
+
+  lm::WordIndex MapWord(const WordID w) const {
+    if (w < cdec2klm_map_.size()) return cdec2klm_map_[w];
+    return 0;
+  }
+
+  ~FixedNgramBaseImpl() { delete model; }
+
+  prob_t StringProbability(const vector<WordID>& s) const {
+    lm::ngram::State state = model->BeginSentenceState();
+    double prob = 0;
+    for (unsigned i = 0; i < s.size(); ++i) {
+      const lm::ngram::State scopy(state);
+      prob += model->Score(scopy, MapWord(s[i]), state);
+    }
+    const lm::ngram::State scopy(state);
+    prob += model->Score(scopy, kEOS, state);
+    prob_t p; p.logeq(prob * log(10));
+    return p;
+  }
+
+  lm::ngram::ProbingModel* model;
+  unsigned order;
+  vector<lm::WordIndex> cdec2klm_map_;
+  lm::WordIndex kEOS;
+};
+
+FixedNgramBase::~FixedNgramBase() { delete impl; }
+
+FixedNgramBase::FixedNgramBase(const string& lmfname) {
+  impl = new FixedNgramBaseImpl(lmfname);
+}
+
+prob_t FixedNgramBase::StringProbability(const vector<WordID>& s) const {
+  return impl->StringProbability(s);
+}
+
-- 
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