From 9f34384f610e512488df4bb0f08e962ad95d6d13 Mon Sep 17 00:00:00 2001
From: graehl <graehl@ec762483-ff6d-05da-a07a-a48fb63a330f>
Date: Tue, 27 Jul 2010 04:59:37 +0000
Subject: fsa feature templated Accum interface, phrase interface allows
 exceeding markov order e.g. unigram state, 3gram lm.  use Accum,set_value
 rather than clear,add_value.  warning: 3gram fsa lm disagrees with bottom-up
 in 4th decimal place

git-svn-id: https://ws10smt.googlecode.com/svn/trunk@431 ec762483-ff6d-05da-a07a-a48fb63a330f
---
 decoder/ff_lm_fsa.h | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 90 insertions(+), 5 deletions(-)

(limited to 'decoder/ff_lm_fsa.h')

diff --git a/decoder/ff_lm_fsa.h b/decoder/ff_lm_fsa.h
index 55a8b497..3547d75b 100755
--- a/decoder/ff_lm_fsa.h
+++ b/decoder/ff_lm_fsa.h
@@ -1,27 +1,112 @@
 #ifndef FF_LM_FSA_H
 #define FF_LM_FSA_H
 
-//TODO: use SRI LM::contextID to shorten state
-//TODO: expose ScanPhrase interface to achieve > ngram probs (e.g. unigram) with higher order lm - but that wouldn't apply to L->R maximal hook/sharing decoding
+//FIXME: 3gram has differences in 4th decimal digit, compared to regular ff_lm.  this is USUALLY a bug (there's way more actual precision in there).  this was with #define LM_FSA_SHORTEN_CONTEXT 1
+
+
+#define FSA_LM_DEBUG 0
+#if FSA_LM_DEBUG
+# define FSALMDBG(e,x) FSADBGif(debug(),e,x)
+# define FSALMDBGnl(e) FSADBGif_nl(debug(),e)
+#else
+# define FSALMDBG(e,x)
+# define FSALMDBGnl(e)
+#endif
 
 #include "ff_lm.h"
 #include "ff_from_fsa.h"
 
+namespace {
+WordID empty_context=TD::none;
+}
+
 struct LanguageModelFsa : public FsaFeatureFunctionBase<LanguageModelFsa> {
+  typedef WordID * W;
+  typedef WordID const* WP;
+
   // overrides; implementations in ff_lm.cc
+  typedef SingleFeatureAccumulator Accum;
   static std::string usage(bool,bool);
   LanguageModelFsa(std::string const& param);
   int markov_order() const { return ctxlen_; }
-  void Scan(SentenceMetadata const& /* smeta */,const Hypergraph::Edge& /* edge */,WordID w,void const* old_st,void *new_st,FeatureVector *features) const;
-  void print_state(std::ostream &,void *) const;
+  void print_state(std::ostream &,void const *) const;
+  inline Featval floored(Featval p) const {
+    return p<floor_?floor_:p;
+  }
+  static inline WordID const* left_end(WordID const* left, WordID const* e) {
+    for (;e>left;--e)
+      if (e[-1]!=TD::none) break;
+    //post: [left,e] are the seen left words
+    return e;
+  }
+  template <class Accum>
+  void ScanPhraseAccum(SentenceMetadata const& /* smeta */,const Hypergraph::Edge&edge,WordID const* begin,WordID const* end,void const* old_st,void *new_st,Accum *a) const {
+    if (begin==end) return; // otherwise w/ shortening it's possible to end up with no words at all.
+    /* // this is forcing unigram prob always.  we will instead build the phrase
+    if (!ctxlen_) {
+      Featval p=0;
+      for (;i<end;++i)
+        p+=floored(pimpl_->WordProb(*i,e&mpty_context));
+      Add(p,a);
+      return;
+      } */
+    int nw=end-begin;
+    WP st=(WP)old_st;
+    WP st_end=st+ctxlen_; // may include some null already (or none if full)
+    int nboth=nw+ctxlen_;
+    WordID ctx[nboth+1];
+    ctx[nboth]=TD::none;
+    // reverse order - state at very end of context, then [i,end) in rev order ending at ctx[0]
+    wordcpy_reverse(ctx,begin,end);
+    W ctx_score_end=ctx+nw;
+    wordcpy(ctx_score_end,st,st_end); // st already reversed
+//    FSALMDBG(edge," Scan("<<TD::GetString(ctx,ctx+nboth)<<')');
+    Featval p=0;
+    FSALMDBGnl(edge);
+    for(;ctx_score_end>ctx;--ctx_score_end)
+      p+=floored(pimpl_->WordProb(ctx_score_end[-1],ctx_score_end));
+#if LM_FSA_SHORTEN_CONTEXT
+    p+=pimpl_->ShortenContext(ctx,nboth<ctxlen_?nboth:ctxlen_);
+#endif
+    state_copy(new_st,ctx);
+    FSALMDBG(edge," lm.Scan("<<TD::GetString(begin,end)<<"|"<<describe_state(old_st)<<")"<<"="<<p<<","<<describe_state(new_st));
+    FSALMDBGnl(edge);
+    Add(p,a);
+  }
+  template <class Accum>
+  void ScanAccum(SentenceMetadata const& /* smeta */,const Hypergraph::Edge& /* edge */,WordID w,void const* old_st,void *new_st,Accum *a) const {
+    if (!ctxlen_) {
+      Add(floored(pimpl_->WordProb(w,&empty_context)),a);
+      return;
+    }
+    //variable length array is in C99, msvc++, if it doesn't support it, #ifdef it or use a stackalloc call (forget the name)
+    if (ctxlen_) {
+      WordID ctx[ngram_order_];
+      state_copy(ctx,old_st);
+      ctx[ctxlen_]=TD::none; // make this part of state?  wastes space but saves copies.
+      Featval p=pimpl_->WordProb(w,ctx);
+// states are sri contexts so are in reverse order (most recent word is first, then 1-back comes next, etc.).
+      WordID *nst=(WordID *)new_st;
+      nst[0]=w; // new most recent word
+      to_state(nst+1,ctx,ctxlen_-1); // rotate old words right
+#if LM_FSA_SHORTEN_CONTEXT
+      p+=pimpl_->ShortenContext(nst,ctxlen_);
+#endif
+      Add(floored(p),a);
+    }
+  }
 
   // impl details:
   void set_ngram_order(int i); // if you build ff_from_fsa first, then increase this, you will get memory overflows.  otherwise, it's the same as a "-o i" argument to constructor
   double floor_; // log10prob minimum used (e.g. unk words)
+
 private:
   int ngram_order_;
   int ctxlen_; // 1 less than above
-  LanguageModelImpl *pimpl_;
+  LanguageModelInterface *pimpl_;
+public:
+  SCAN_PHRASE_ACCUM_OVERRIDE
+
 };
 
 typedef FeatureFunctionFromFsa<LanguageModelFsa> LanguageModelFromFsa;
-- 
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