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#ifndef FF_LM_FSA_H
#define FF_LM_FSA_H
//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 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
LanguageModelInterface *pimpl_;
public:
SCAN_PHRASE_ACCUM_OVERRIDE
};
typedef FeatureFunctionFromFsa<LanguageModelFsa> LanguageModelFromFsa;
#endif
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