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// finite-state transducer library.
//
// Functions and classes to determinize an FST.
#ifndef FST_LIB_DETERMINIZE_H_
#define FST_LIB_DETERMINIZE_H_
#include <algorithm>
#include <climits>
#include <forward_list>
#include <map>
#include <string>
#include <vector>
#include <fst/arc-map.h>
#include <fst/bi-table.h>
#include <fst/cache.h>
#include <fst/factor-weight.h>
#include <fst/filter-state.h>
#include <fst/prune.h>
#include <fst/test-properties.h>
namespace fst {
//
// COMMON DIVISORS - these are used in determinization to compute
// the transition weights. In the simplest case, it is just the same
// as the semiring Plus(). However, other choices permit more efficient
// determinization when the output contains strings.
//
// The default common divisor uses the semiring Plus.
template <class W>
class DefaultCommonDivisor {
public:
typedef W Weight;
W operator()(const W &w1, const W &w2) const { return Plus(w1, w2); }
};
// The label common divisor for a (left) string semiring selects a
// single letter common prefix or the empty string. This is used in
// the determinization of output strings so that at most a single
// letter will appear in the output of a transtion.
template <typename L, StringType S>
class LabelCommonDivisor {
public:
typedef StringWeight<L, S> Weight;
Weight operator()(const Weight &w1, const Weight &w2) const {
StringWeightIterator<L, S> iter1(w1);
StringWeightIterator<L, S> iter2(w2);
if (!(StringWeight<L, S>::Properties() & kLeftSemiring)) {
FSTERROR() << "LabelCommonDivisor: Weight needs to be left semiring";
return Weight::NoWeight();
} else if (w1.Size() == 0 || w2.Size() == 0) {
return Weight::One();
} else if (w1 == Weight::Zero()) {
return Weight(iter2.Value());
} else if (w2 == Weight::Zero()) {
return Weight(iter1.Value());
} else if (iter1.Value() == iter2.Value()) {
return Weight(iter1.Value());
} else {
return Weight::One();
}
}
};
// The gallic common divisor uses the label common divisor on the
// string component and the template argument D common divisor on the
// weight component, which defaults to the default common divisor.
template <class L, class W, GallicType G, class D = DefaultCommonDivisor<W>>
class GallicCommonDivisor {
public:
typedef GallicWeight<L, W, G> Weight;
Weight operator()(const Weight &w1, const Weight &w2) const {
return Weight(label_common_divisor_(w1.Value1(), w2.Value1()),
weight_common_divisor_(w1.Value2(), w2.Value2()));
}
private:
LabelCommonDivisor<L, GALLIC_STRING_TYPE(G)> label_common_divisor_;
D weight_common_divisor_;
};
// Specialization for general GALLIC weight.
template <class L, class W, class D>
class GallicCommonDivisor<L, W, GALLIC, D> {
public:
typedef GallicWeight<L, W, GALLIC> Weight;
typedef GallicWeight<L, W, GALLIC_RESTRICT> GRWeight;
typedef UnionWeightIterator<GRWeight, GallicUnionWeightOptions<L, W>> Iter;
Weight operator()(const Weight &w1, const Weight &w2) const {
GRWeight w = GRWeight::Zero();
for (Iter iter(w1); !iter.Done(); iter.Next())
w = common_divisor_(w, iter.Value());
for (Iter iter(w2); !iter.Done(); iter.Next())
w = common_divisor_(w, iter.Value());
return w == GRWeight::Zero() ? Weight::Zero() : Weight(w);
}
private:
GallicCommonDivisor<L, W, GALLIC_RESTRICT, D> common_divisor_;
};
// Represents an element in a subset
template <class A>
struct DeterminizeElement {
typedef typename A::StateId StateId;
typedef typename A::Weight Weight;
DeterminizeElement() {}
DeterminizeElement(StateId s, Weight w) : state_id(s), weight(w) {}
bool operator==(const DeterminizeElement<A> &element) const {
return state_id == element.state_id && weight == element.weight;
}
bool operator!=(const DeterminizeElement<A> &element) const {
return !(*this == element);
}
bool operator<(const DeterminizeElement<A> &element) const {
return state_id < element.state_id;
}
StateId state_id; // Input state Id
Weight weight; // Residual weight
};
// Represents a weighted subset and determinization filter state
template <typename A, typename F>
struct DeterminizeStateTuple {
typedef A Arc;
typedef F FilterState;
typedef DeterminizeElement<Arc> Element;
typedef std::forward_list<Element> Subset;
DeterminizeStateTuple() : filter_state(FilterState::NoState()) {}
bool operator==(const DeterminizeStateTuple<A, F> &tuple) const {
return (tuple.filter_state == filter_state) && (tuple.subset == subset);
}
bool operator!=(const DeterminizeStateTuple<A, F> &tuple) const {
return (tuple.filter_state != filter_state) || (tuple.subset != subset);
}
Subset subset;
FilterState filter_state;
};
// Proto-transition for determinization
template <class S>
struct DeterminizeArc {
typedef S StateTuple;
typedef typename S::Arc Arc;
typedef typename Arc::Label Label;
typedef typename Arc::Weight Weight;
DeterminizeArc() : label(kNoLabel), weight(Weight::Zero()), dest_tuple(0) {}
explicit DeterminizeArc(const Arc &arc)
: label(arc.ilabel), weight(Weight::Zero()), dest_tuple(new S) {}
Label label; // arc label
Weight weight; // arc weight
StateTuple *dest_tuple; // destination subset and filter state
};
//
// DETERMINIZE FILTERS - these are used in determinization to compute
// destination state tuples based on the source tuple, transition, and
// destination element or on similar super-final transition
// information. The filter operates on a map between a label and the
// corresponding destination state tuples. It must define the map type
// LabelMap. The default filter is used for weighted determinization.
//
// A determinize filter for implementing weighted determinization.
template <class Arc>
class DefaultDeterminizeFilter {
public:
typedef typename Arc::StateId StateId;
typedef typename Arc::Label Label;
typedef typename Arc::Weight Weight;
typedef CharFilterState FilterState;
typedef DeterminizeElement<Arc> Element;
typedef DeterminizeStateTuple<Arc, FilterState> StateTuple;
typedef std::map<Label, DeterminizeArc<StateTuple>> LabelMap;
// This is needed e.g. to go into the gallic domain for transducers.
template <class A>
struct rebind {
typedef DefaultDeterminizeFilter<A> other;
};
DefaultDeterminizeFilter(const Fst<Arc> &fst) : fst_(fst.Copy()) {}
// This is needed e.g. to go into the gallic domain for transducers.
// Ownership of the templated filter argument is given to this class.
template <class F>
DefaultDeterminizeFilter(const Fst<Arc> &fst, F *filter) : fst_(fst.Copy()) {
delete filter;
}
// Copy ctr. The FST can be passed if it has been e.g. (deep) copied.
explicit DefaultDeterminizeFilter(const DefaultDeterminizeFilter<Arc> &filter,
const Fst<Arc> *fst = 0)
: fst_(fst ? fst->Copy() : filter.fst_->Copy()) {}
~DefaultDeterminizeFilter() { delete fst_; }
FilterState Start() const { return FilterState(0); }
void SetState(StateId s, const StateTuple &tuple) {}
// Filters transition, possibly modifying label map. Returns
// true if arc is added to label map.
bool FilterArc(const Arc &arc, const Element &src_element,
const Element &dest_element, LabelMap *label_map) const {
// Adds element to unique state tuple for arc label; create if necessary
DeterminizeArc<StateTuple> &det_arc = (*label_map)[arc.ilabel];
if (det_arc.label == kNoLabel) {
det_arc = DeterminizeArc<StateTuple>(arc);
det_arc.dest_tuple->filter_state = FilterState(0);
}
det_arc.dest_tuple->subset.push_front(dest_element);
return true;
}
// Filters super-final transition, returning new final weight
Weight FilterFinal(Weight final_weight, const Element &element) {
return final_weight;
}
static uint64 Properties(uint64 props) { return props; }
private:
Fst<Arc> *fst_;
void operator=(const DefaultDeterminizeFilter<Arc> &); // disallow
};
//
// DETERMINIZATION STATE TABLES
//
// The determinization state table has the form:
//
// template <class A, class F>
// class DeterminizeStateTable {
// public:
// typename A Arc;
// typename F FilterState;
// typedef typename Arc::StateId StateId;
// typedef DeterminizeStateTuple<Arc, FilterState> StateTuple;
//
// // Required sub-class. This is needed e.g. to go into the gallic domain.
// template <class B, class G>
// struct rebind { typedef DeterminizeStateTable<B, G> other; };
//
// // Required constuctor
// DeterminizeStateTable();
//
// // Required copy constructor that does not copy state
// DeterminizeStateTable(const DeterminizeStateTable<A,F> &table);
//
// // Lookup state ID by state tuple.
// // If it doesn't exist, then add it. FindState takes ownership
// // of the state tuple argument (so that it doesn't have to
// // copy it if it creates a new state).
// StateId FindState(StateTuple *tuple);
//
// // Lookup state tuple by ID.
// const StateTuple *Tuple(StateId id) const;
// };
// The default determinization state table based on the
// compact hash bi-table.
template <class A, class F>
class DefaultDeterminizeStateTable {
public:
typedef A Arc;
typedef F FilterState;
typedef typename Arc::StateId StateId;
typedef typename Arc::Label Label;
typedef typename Arc::Weight Weight;
typedef DeterminizeStateTuple<Arc, FilterState> StateTuple;
typedef typename StateTuple::Subset Subset;
typedef typename StateTuple::Element Element;
template <class B, class G>
struct rebind {
typedef DefaultDeterminizeStateTable<B, G> other;
};
explicit DefaultDeterminizeStateTable(size_t table_size = 0)
: table_size_(table_size), tuples_(table_size_) {}
DefaultDeterminizeStateTable(const DefaultDeterminizeStateTable<A, F> &table)
: table_size_(table.table_size_), tuples_(table_size_) {}
~DefaultDeterminizeStateTable() {
for (StateId s = 0; s < tuples_.Size(); ++s) delete tuples_.FindEntry(s);
}
// Finds the state corresponding to a state tuple. Only creates a new
// state if the tuple is not found. FindState takes ownership of
// the tuple argument (so that it doesn't have to copy it if it
// creates a new state).
StateId FindState(StateTuple *tuple) {
StateId ns = tuples_.Size();
StateId s = tuples_.FindId(tuple);
if (s != ns) delete tuple; // tuple found
return s;
}
const StateTuple *Tuple(StateId s) { return tuples_.FindEntry(s); }
private:
// Comparison object for StateTuples.
class StateTupleEqual {
public:
bool operator()(const StateTuple *tuple1, const StateTuple *tuple2) const {
return *tuple1 == *tuple2;
}
};
// Hash function for StateTuples.
class StateTupleKey {
public:
size_t operator()(const StateTuple *tuple) const {
size_t h = tuple->filter_state.Hash();
for (typename Subset::const_iterator iter = tuple->subset.begin();
iter != tuple->subset.end(); ++iter) {
const Element &element = *iter;
size_t h1 = element.state_id;
size_t h2 = element.weight.Hash();
const int lshift = 5;
const int rshift = CHAR_BIT * sizeof(size_t) - 5;
h ^= h << 1 ^ h1 << lshift ^ h1 >> rshift ^ h2;
}
return h;
}
};
size_t table_size_;
typedef CompactHashBiTable<StateId, StateTuple *, StateTupleKey,
StateTupleEqual, HS_STL> StateTupleTable;
StateTupleTable tuples_;
void operator=(const DefaultDeterminizeStateTable<A, F> &); // disallow
};
// Type of determinization
enum DeterminizeType {
DETERMINIZE_FUNCTIONAL, // Input transducer is functional (error if not)
DETERMINIZE_NONFUNCTIONAL, // Input transducer is not known to be functional
DETERMINIZE_DISAMBIGUATE // Input transducer is non-functional but only
// keep the min of ambiguous outputs.
};
// Options for finite-state transducer determinization templated on
// the arc type, common divisor, the determinization filter and the
// state table. DeterminizeFst takes ownership of the determinization
// filter and state table if provided.
template <class Arc, class D = DefaultCommonDivisor<typename Arc::Weight>,
class F = DefaultDeterminizeFilter<Arc>,
class T = DefaultDeterminizeStateTable<Arc, typename F::FilterState>>
struct DeterminizeFstOptions : CacheOptions {
typedef typename Arc::Label Label;
float delta; // Quantization delta for subset weights
Label subsequential_label; // Label used for residual final output
// when producing subsequential transducers.
DeterminizeType type; // Determinization type
bool increment_subsequential_label; // When creating several subsequential
// arcs at a given state, make their
// label distinct by incrementing.
F *filter; // Determinization filter
T *state_table; // Determinization state table
explicit DeterminizeFstOptions(const CacheOptions &opts, float del = kDelta,
Label lab = 0,
DeterminizeType typ = DETERMINIZE_FUNCTIONAL,
bool inc_lab = false, F *filt = 0,
T *table = 0)
: CacheOptions(opts),
delta(del),
subsequential_label(lab),
type(typ),
increment_subsequential_label(inc_lab),
filter(filt),
state_table(table) {}
explicit DeterminizeFstOptions(float del = kDelta, Label lab = 0,
DeterminizeType typ = DETERMINIZE_FUNCTIONAL,
bool inc_lab = false, F *filt = 0,
T *table = 0)
: delta(del),
subsequential_label(lab),
type(typ),
increment_subsequential_label(inc_lab),
filter(filt),
state_table(table) {}
};
// Implementation of delayed DeterminizeFst. This base class is
// common to the variants that implement acceptor and transducer
// determinization.
template <class A>
class DeterminizeFstImplBase : public CacheImpl<A> {
public:
using FstImpl<A>::SetType;
using FstImpl<A>::SetProperties;
using FstImpl<A>::Properties;
using FstImpl<A>::SetInputSymbols;
using FstImpl<A>::SetOutputSymbols;
using CacheBaseImpl<CacheState<A>>::HasStart;
using CacheBaseImpl<CacheState<A>>::HasFinal;
using CacheBaseImpl<CacheState<A>>::HasArcs;
using CacheBaseImpl<CacheState<A>>::SetFinal;
using CacheBaseImpl<CacheState<A>>::SetStart;
typedef typename A::Label Label;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef DefaultCacheStore<A> Store;
typedef typename Store::State State;
template <class D, class F, class T>
DeterminizeFstImplBase(const Fst<A> &fst,
const DeterminizeFstOptions<A, D, F, T> &opts)
: CacheImpl<A>(opts), fst_(fst.Copy()) {
SetType("determinize");
uint64 iprops = fst.Properties(kFstProperties, false);
uint64 dprops =
DeterminizeProperties(iprops, opts.subsequential_label != 0,
opts.type == DETERMINIZE_NONFUNCTIONAL
? opts.increment_subsequential_label
: true);
SetProperties(F::Properties(dprops), kCopyProperties);
SetInputSymbols(fst.InputSymbols());
SetOutputSymbols(fst.OutputSymbols());
}
DeterminizeFstImplBase(const DeterminizeFstImplBase<A> &impl)
: CacheImpl<A>(impl), fst_(impl.fst_->Copy(true)) {
SetType("determinize");
SetProperties(impl.Properties(), kCopyProperties);
SetInputSymbols(impl.InputSymbols());
SetOutputSymbols(impl.OutputSymbols());
}
~DeterminizeFstImplBase() override { delete fst_; }
virtual DeterminizeFstImplBase<A> *Copy() const = 0;
StateId Start() {
if (!HasStart()) {
StateId start = ComputeStart();
if (start != kNoStateId) {
SetStart(start);
}
}
return CacheImpl<A>::Start();
}
Weight Final(StateId s) {
if (!HasFinal(s)) {
Weight final = ComputeFinal(s);
SetFinal(s, final);
}
return CacheImpl<A>::Final(s);
}
virtual void Expand(StateId s) = 0;
size_t NumArcs(StateId s) {
if (!HasArcs(s)) Expand(s);
return CacheImpl<A>::NumArcs(s);
}
size_t NumInputEpsilons(StateId s) {
if (!HasArcs(s)) Expand(s);
return CacheImpl<A>::NumInputEpsilons(s);
}
size_t NumOutputEpsilons(StateId s) {
if (!HasArcs(s)) Expand(s);
return CacheImpl<A>::NumOutputEpsilons(s);
}
void InitArcIterator(StateId s, ArcIteratorData<A> *data) {
if (!HasArcs(s)) Expand(s);
CacheImpl<A>::InitArcIterator(s, data);
}
virtual StateId ComputeStart() = 0;
virtual Weight ComputeFinal(StateId s) = 0;
const Fst<A> &GetFst() const { return *fst_; }
private:
const Fst<A> *fst_; // Input Fst
void operator=(const DeterminizeFstImplBase<A> &); // disallow
};
// Implementation of delayed determinization for weighted acceptors.
// It is templated on the arc type A and the common divisor D.
template <class A, class D, class F, class T>
class DeterminizeFsaImpl : public DeterminizeFstImplBase<A> {
public:
using FstImpl<A>::SetProperties;
using DeterminizeFstImplBase<A>::GetFst;
using DeterminizeFstImplBase<A>::SetArcs;
typedef typename A::Label Label;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef typename F::FilterState FilterState;
typedef DeterminizeStateTuple<A, FilterState> StateTuple;
typedef typename StateTuple::Element Element;
typedef typename StateTuple::Subset Subset;
typedef typename F::LabelMap LabelMap;
DeterminizeFsaImpl(const Fst<A> &fst, const std::vector<Weight> *in_dist,
std::vector<Weight> *out_dist,
const DeterminizeFstOptions<A, D, F, T> &opts)
: DeterminizeFstImplBase<A>(fst, opts),
delta_(opts.delta),
in_dist_(in_dist),
out_dist_(out_dist),
filter_(opts.filter ? opts.filter : new F(fst)),
state_table_(opts.state_table ? opts.state_table : new T()) {
if (!fst.Properties(kAcceptor, true)) {
FSTERROR() << "DeterminizeFst: Argument not an acceptor";
SetProperties(kError, kError);
}
if (!(Weight::Properties() & kLeftSemiring)) {
FSTERROR() << "DeterminizeFst: Weight needs to be left distributive: "
<< Weight::Type();
SetProperties(kError, kError);
}
if (out_dist_) out_dist_->clear();
}
DeterminizeFsaImpl(const DeterminizeFsaImpl<A, D, F, T> &impl)
: DeterminizeFstImplBase<A>(impl),
delta_(impl.delta_),
in_dist_(0),
out_dist_(0),
filter_(new F(*impl.filter_, &GetFst())),
state_table_(new T(*impl.state_table_)) {
if (impl.out_dist_) {
FSTERROR() << "DeterminizeFsaImpl: Cannot copy with out_dist vector";
SetProperties(kError, kError);
}
}
~DeterminizeFsaImpl() override {
delete filter_;
delete state_table_;
}
DeterminizeFsaImpl<A, D, F, T> *Copy() const override {
return new DeterminizeFsaImpl<A, D, F, T>(*this);
}
uint64 Properties() const override { return Properties(kFstProperties); }
// Set error if found; return FST impl properties.
uint64 Properties(uint64 mask) const override {
if ((mask & kError) && (GetFst().Properties(kError, false)))
SetProperties(kError, kError);
return FstImpl<A>::Properties(mask);
}
StateId ComputeStart() override {
StateId s = GetFst().Start();
if (s == kNoStateId) return kNoStateId;
Element element(s, Weight::One());
StateTuple *tuple = new StateTuple;
tuple->subset.push_front(element);
tuple->filter_state = filter_->Start();
return FindState(tuple);
}
Weight ComputeFinal(StateId s) override {
const StateTuple *tuple = state_table_->Tuple(s);
filter_->SetState(s, *tuple);
Weight final = Weight::Zero();
for (typename Subset::const_iterator siter = tuple->subset.begin();
siter != tuple->subset.end(); ++siter) {
const Element &element = *siter;
final =
Plus(final, Times(element.weight, GetFst().Final(element.state_id)));
final = filter_->FilterFinal(final, element);
if (!final.Member()) SetProperties(kError, kError);
}
return final;
}
StateId FindState(StateTuple *tuple) {
StateId s = state_table_->FindState(tuple);
if (in_dist_ && out_dist_->size() <= s)
out_dist_->push_back(ComputeDistance(tuple->subset));
return s;
}
// Compute distance from a state to the final states in the DFA
// given the distances in the NFA.
Weight ComputeDistance(const Subset &subset) {
Weight outd = Weight::Zero();
for (typename Subset::const_iterator siter = subset.begin();
siter != subset.end(); ++siter) {
const Element &element = *siter;
Weight ind = element.state_id < in_dist_->size()
? (*in_dist_)[element.state_id]
: Weight::Zero();
outd = Plus(outd, Times(element.weight, ind));
}
return outd;
}
// Computes the outgoing transitions from a state, creating new destination
// states as needed.
void Expand(StateId s) override {
LabelMap label_map;
GetLabelMap(s, &label_map);
for (auto liter = label_map.begin(); liter != label_map.end(); ++liter) {
AddArc(s, liter->second);
}
SetArcs(s);
}
private:
// Constructs proto determinization transition, including
// destination subset, per label.
void GetLabelMap(StateId s, LabelMap *label_map) {
const StateTuple *src_tuple = state_table_->Tuple(s);
filter_->SetState(s, *src_tuple);
for (typename Subset::const_iterator siter = src_tuple->subset.begin();
siter != src_tuple->subset.end(); ++siter) {
const Element &src_element = *siter;
for (ArcIterator<Fst<A>> aiter(GetFst(), src_element.state_id);
!aiter.Done(); aiter.Next()) {
const A &arc = aiter.Value();
Element dest_element(arc.nextstate,
Times(src_element.weight, arc.weight));
filter_->FilterArc(arc, src_element, dest_element, label_map);
}
}
for (auto liter = label_map->begin(); liter != label_map->end(); ++liter) {
NormArc(&liter->second);
}
}
// Sorts subsets and removes duplicate elements.
// Normalizes transition and subset weights.
void NormArc(DeterminizeArc<StateTuple> *det_arc) {
StateTuple *dest_tuple = det_arc->dest_tuple;
dest_tuple->subset.sort();
auto piter = dest_tuple->subset.begin();
for (auto diter = dest_tuple->subset.begin();
diter != dest_tuple->subset.end();) {
Element &dest_element = *diter;
Element &prev_element = *piter;
// Computes arc weight.
det_arc->weight = common_divisor_(det_arc->weight, dest_element.weight);
if (piter != diter && dest_element.state_id == prev_element.state_id) {
// Found duplicate state: sums state weight and deletes dup.
prev_element.weight = Plus(prev_element.weight, dest_element.weight);
if (!prev_element.weight.Member()) SetProperties(kError, kError);
++diter;
dest_tuple->subset.erase_after(piter);
} else {
piter = diter;
++diter;
}
}
// Divides out label weight from destination subset elements.
// Quantizes to ensure comparisons are effective.
for (auto diter = dest_tuple->subset.begin();
diter != dest_tuple->subset.end(); ++diter) {
Element &dest_element = *diter;
dest_element.weight =
Divide(dest_element.weight, det_arc->weight, DIVIDE_LEFT);
dest_element.weight = dest_element.weight.Quantize(delta_);
}
}
// Adds an arc from state S to the destination state associated
// with state tuple in DET_ARC (as created by GetLabelMap).
void AddArc(StateId s, const DeterminizeArc<StateTuple> &det_arc) {
A arc;
arc.ilabel = det_arc.label;
arc.olabel = det_arc.label;
arc.weight = det_arc.weight;
arc.nextstate = FindState(det_arc.dest_tuple);
CacheImpl<A>::PushArc(s, arc);
}
float delta_; // Quantization delta for subset weights
const std::vector<Weight> *in_dist_; // Distance to final NFA states
std::vector<Weight> *out_dist_; // Distance to final DFA states
D common_divisor_;
F *filter_;
T *state_table_;
void operator=(const DeterminizeFsaImpl<A, D, F, T> &); // disallow
};
// Implementation of delayed determinization for transducers.
// Transducer determinization is implemented by mapping the input to
// the Gallic semiring as an acceptor whose weights contain the output
// strings and using acceptor determinization above to determinize
// that acceptor.
template <class A, GallicType G, class D, class F, class T>
class DeterminizeFstImpl : public DeterminizeFstImplBase<A> {
public:
using FstImpl<A>::SetProperties;
using DeterminizeFstImplBase<A>::GetFst;
using CacheBaseImpl<CacheState<A>>::GetCacheGc;
using CacheBaseImpl<CacheState<A>>::GetCacheLimit;
typedef typename A::Label Label;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef ToGallicMapper<A, G> ToMapper;
typedef FromGallicMapper<A, G> FromMapper;
typedef typename ToMapper::ToArc ToArc;
typedef ArcMapFst<A, ToArc, ToMapper> ToFst;
typedef ArcMapFst<ToArc, A, FromMapper> FromFst;
typedef GallicCommonDivisor<Label, Weight, G, D> ToD;
typedef typename F::template rebind<ToArc>::other ToF;
typedef typename ToF::FilterState ToFilterState;
typedef typename T::template rebind<ToArc, ToFilterState>::other ToT;
typedef GallicFactor<Label, Weight, G> FactorIterator;
DeterminizeFstImpl(const Fst<A> &fst,
const DeterminizeFstOptions<A, D, F, T> &opts)
: DeterminizeFstImplBase<A>(fst, opts),
delta_(opts.delta),
subsequential_label_(opts.subsequential_label),
increment_subsequential_label_(opts.increment_subsequential_label) {
if (opts.state_table) {
FSTERROR() << "DeterminizeFst: "
<< "A state table can not be passed with transducer input";
SetProperties(kError, kError);
return;
}
Init(GetFst(), opts.filter);
}
DeterminizeFstImpl(const DeterminizeFstImpl<A, G, D, F, T> &impl)
: DeterminizeFstImplBase<A>(impl),
delta_(impl.delta_),
subsequential_label_(impl.subsequential_label_),
increment_subsequential_label_(impl.increment_subsequential_label_) {
Init(GetFst(), 0);
}
~DeterminizeFstImpl() override { delete from_fst_; }
DeterminizeFstImpl<A, G, D, F, T> *Copy() const override {
return new DeterminizeFstImpl<A, G, D, F, T>(*this);
}
uint64 Properties() const override { return Properties(kFstProperties); }
// Set error if found; return FST impl properties.
uint64 Properties(uint64 mask) const override {
if ((mask & kError) && (GetFst().Properties(kError, false) ||
from_fst_->Properties(kError, false)))
SetProperties(kError, kError);
return FstImpl<A>::Properties(mask);
}
StateId ComputeStart() override { return from_fst_->Start(); }
Weight ComputeFinal(StateId s) override { return from_fst_->Final(s); }
void Expand(StateId s) override {
for (ArcIterator<FromFst> aiter(*from_fst_, s); !aiter.Done(); aiter.Next())
CacheImpl<A>::PushArc(s, aiter.Value());
CacheImpl<A>::SetArcs(s);
}
private:
// Initialization of transducer determinization implementation, which
// is defined after DeterminizeFst since it calls it.
void Init(const Fst<A> &fst, F *filter);
float delta_;
Label subsequential_label_;
bool increment_subsequential_label_;
FromFst *from_fst_;
void operator=(const DeterminizeFstImpl<A, G, D, F, T> &); // disallow
};
// Determinizes a weighted transducer. This version is a delayed
// Fst. The result will be an equivalent FST that has the property
// that no state has two transitions with the same input label.
// For this algorithm, epsilon transitions are treated as regular
// symbols (cf. RmEpsilon).
//
// The transducer must be functional. The weights must be (weakly)
// left divisible (valid for TropicalWeight and LogWeight for instance)
// and be zero-sum-free if for all a,b: (Plus(a, b) = 0 => a = b = 0.
//
// Complexity:
// - Determinizable: exponential (polynomial in the size of the output)
// - Non-determinizable) does not terminate
//
// The determinizable automata include all unweighted and all acyclic input.
//
// References:
// - Mehryar Mohri, "Finite-State Transducers in Language and Speech
// Processing". Computational Linguistics, 23:2, 1997.
//
// This class attaches interface to implementation and handles
// reference counting, delegating most methods to ImplToFst.
template <class A>
class DeterminizeFst : public ImplToFst<DeterminizeFstImplBase<A>> {
public:
friend class ArcIterator<DeterminizeFst<A>>;
friend class StateIterator<DeterminizeFst<A>>;
template <class B, GallicType G, class D, class F, class T>
friend class DeterminizeFstImpl;
typedef A Arc;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef typename A::Label Label;
typedef DefaultCacheStore<A> Store;
typedef typename Store::State State;
typedef DeterminizeFstImplBase<A> Impl;
explicit DeterminizeFst(const Fst<A> &fst)
: ImplToFst<Impl>(CreateImpl(fst)) {}
template <class D, class F, class T>
DeterminizeFst(const Fst<A> &fst,
const DeterminizeFstOptions<A, D, F, T> &opts)
: ImplToFst<Impl>(CreateImpl(fst, opts)) {}
// This acceptor-only version additionally computes the distance to
// final states in the output if provided with those distances for the
// input. Useful for e.g. unique N-shortest paths.
template <class D, class F, class T>
DeterminizeFst(const Fst<A> &fst, const std::vector<Weight> *in_dist,
std::vector<Weight> *out_dist,
const DeterminizeFstOptions<A, D, F, T> &opts)
: ImplToFst<Impl>(std::make_shared<DeterminizeFsaImpl<A, D, F, T>>(
fst, in_dist, out_dist, opts)) {
if (!fst.Properties(kAcceptor, true)) {
FSTERROR() << "DeterminizeFst: "
<< "Distance to final states computed for acceptors only";
GetMutableImpl()->SetProperties(kError, kError);
}
}
// See Fst<>::Copy() for doc.
DeterminizeFst(const DeterminizeFst<A> &fst, bool safe = false)
: ImplToFst<Impl>(safe ? std::shared_ptr<Impl>(fst.GetImpl()->Copy())
: fst.GetSharedImpl()) {}
// Get a copy of this DeterminizeFst. See Fst<>::Copy() for further doc.
DeterminizeFst<A> *Copy(bool safe = false) const override {
return new DeterminizeFst<A>(*this, safe);
}
inline void InitStateIterator(StateIteratorData<A> *data) const override;
void InitArcIterator(StateId s, ArcIteratorData<A> *data) const override {
GetMutableImpl()->InitArcIterator(s, data);
}
private:
using ImplToFst<Impl>::GetImpl;
using ImplToFst<Impl>::GetMutableImpl;
static std::shared_ptr<Impl> CreateImpl(const Fst<Arc> &fst) {
typedef DefaultCommonDivisor<Weight> D;
typedef DefaultDeterminizeFilter<A> F;
typedef typename F::FilterState FilterState;
typedef DefaultDeterminizeStateTable<A, FilterState> T;
DeterminizeFstOptions<A, D, F, T> opts;
return CreateImpl(fst, opts);
}
template <class D, class F, class T>
static std::shared_ptr<Impl> CreateImpl(
const Fst<Arc> &fst, const DeterminizeFstOptions<A, D, F, T> &opts) {
if (fst.Properties(kAcceptor, true)) {
// Calls implementation for acceptors.
return std::make_shared<DeterminizeFsaImpl<A, D, F, T>>(fst, nullptr,
nullptr, opts);
} else if (opts.type == DETERMINIZE_DISAMBIGUATE) {
std::shared_ptr<Impl> rv =
std::make_shared<DeterminizeFstImpl<A, GALLIC_MIN, D, F, T>>(fst,
opts);
if (!(Weight::Properties() & kPath)) {
FSTERROR() << "DeterminizeFst: Weight needs to have the "
<< "path property to disambiguate output: "
<< Weight::Type();
rv->SetProperties(kError, kError);
}
// Calls disambiguating implementation for non-functional transducers.
return rv;
} else if (opts.type == DETERMINIZE_FUNCTIONAL) {
// Calls implementation for functional transducers.
return std::make_shared<DeterminizeFstImpl<A, GALLIC_RESTRICT, D, F, T>>(
fst, opts);
} else { // opts.type == DETERMINIZE_NONFUNCTIONAL
// Calls implementation for non functional transducers;
return std::make_shared<DeterminizeFstImpl<A, GALLIC, D, F, T>>(fst,
opts);
}
}
void operator=(const DeterminizeFst<A> &fst); // Disallow
};
// Initialization of transducer determinization implementation, which
// is defined after DeterminizeFst since it calls it.
template <class A, GallicType G, class D, class F, class T>
void DeterminizeFstImpl<A, G, D, F, T>::Init(const Fst<A> &fst, F *filter) {
// Mapper to an acceptor.
ToFst to_fst(fst, ToMapper());
ToF *to_filter = filter ? new ToF(to_fst, filter) : 0;
// Determinizes acceptor.
// This recursive call terminates since it is to a (non-recursive)
// different constructor.
CacheOptions copts(GetCacheGc(), GetCacheLimit());
DeterminizeFstOptions<ToArc, ToD, ToF, ToT> dopts(
copts, delta_, 0, DETERMINIZE_FUNCTIONAL, false, to_filter);
// Uses acceptor-only constructor to avoid template recursion
DeterminizeFst<ToArc> det_fsa(to_fst, 0, 0, dopts);
// Mapper back to transducer.
FactorWeightOptions<ToArc> fopts(
CacheOptions(true, 0), delta_, kFactorFinalWeights, subsequential_label_,
subsequential_label_, increment_subsequential_label_,
increment_subsequential_label_);
FactorWeightFst<ToArc, FactorIterator> factored_fst(det_fsa, fopts);
from_fst_ = new FromFst(factored_fst, FromMapper(subsequential_label_));
}
// Specialization for DeterminizeFst.
template <class A>
class StateIterator<DeterminizeFst<A>>
: public CacheStateIterator<DeterminizeFst<A>> {
public:
explicit StateIterator(const DeterminizeFst<A> &fst)
: CacheStateIterator<DeterminizeFst<A>>(fst, fst.GetMutableImpl()) {}
};
// Specialization for DeterminizeFst.
template <class A>
class ArcIterator<DeterminizeFst<A>>
: public CacheArcIterator<DeterminizeFst<A>> {
public:
typedef typename A::StateId StateId;
ArcIterator(const DeterminizeFst<A> &fst, StateId s)
: CacheArcIterator<DeterminizeFst<A>>(fst.GetMutableImpl(), s) {
if (!fst.GetImpl()->HasArcs(s)) fst.GetMutableImpl()->Expand(s);
}
private:
DISALLOW_COPY_AND_ASSIGN(ArcIterator);
};
template <class A>
inline void DeterminizeFst<A>::InitStateIterator(
StateIteratorData<A> *data) const {
data->base = new StateIterator<DeterminizeFst<A>>(*this);
}
// Useful aliases when using StdArc.
typedef DeterminizeFst<StdArc> StdDeterminizeFst;
template <class Arc>
struct DeterminizeOptions {
typedef typename Arc::StateId StateId;
typedef typename Arc::Weight Weight;
typedef typename Arc::Label Label;
float delta; // Quantization delta for subset weights.
Weight weight_threshold; // Pruning weight threshold.
StateId state_threshold; // Pruning state threshold.
Label subsequential_label; // Label used for residual final output
// when producing subsequential transducers.
DeterminizeType type; // functional, nonfunctional, disambiguate?
bool increment_subsequential_label; // When creating several subsequential
// arcs at a given state, make their label distinct by incrementing.
explicit DeterminizeOptions(float d = kDelta, Weight w = Weight::Zero(),
StateId n = kNoStateId, Label l = 0,
DeterminizeType t = DETERMINIZE_FUNCTIONAL,
bool isl = false)
: delta(d),
weight_threshold(w),
state_threshold(n),
subsequential_label(l),
type(t),
increment_subsequential_label(isl) {}
};
// Determinizes a weighted transducer. This version writes the
// determinized Fst to an output MutableFst. The result will be an
// equivalent FST that has the property that no state has two
// transitions with the same input label. For this algorithm, epsilon
// transitions are treated as regular symbols (cf. RmEpsilon).
//
// The transducer must be functional. The weights must be (weakly)
// left divisible (valid for TropicalWeight and LogWeight).
//
// Complexity:
// - Determinizable: exponential (polynomial in the size of the output)
// - Non-determinizable: does not terminate
//
// The determinizable automata include all unweighted and all acyclic input.
//
// References:
// - Mehryar Mohri, "Finite-State Transducers in Language and Speech
// Processing". Computational Linguistics, 23:2, 1997.
template <class Arc>
void Determinize(
const Fst<Arc> &ifst, MutableFst<Arc> *ofst,
const DeterminizeOptions<Arc> &opts = DeterminizeOptions<Arc>()) {
typedef typename Arc::StateId StateId;
typedef typename Arc::Weight Weight;
DeterminizeFstOptions<Arc> nopts;
nopts.delta = opts.delta;
nopts.subsequential_label = opts.subsequential_label;
nopts.type = opts.type;
nopts.increment_subsequential_label = opts.increment_subsequential_label;
nopts.gc_limit = 0; // Cache only the last state for fastest copy.
if (opts.weight_threshold != Weight::Zero() ||
opts.state_threshold != kNoStateId) {
if (ifst.Properties(kAcceptor, false)) {
std::vector<Weight> idistance, odistance;
ShortestDistance(ifst, &idistance, true);
DeterminizeFst<Arc> dfst(ifst, &idistance, &odistance, nopts);
PruneOptions<Arc, AnyArcFilter<Arc>> popts(
opts.weight_threshold, opts.state_threshold, AnyArcFilter<Arc>(),
&odistance);
Prune(dfst, ofst, popts);
} else {
*ofst = DeterminizeFst<Arc>(ifst, nopts);
Prune(ofst, opts.weight_threshold, opts.state_threshold);
}
} else {
*ofst = DeterminizeFst<Arc>(ifst, nopts);
}
}
} // namespace fst
#endif // FST_LIB_DETERMINIZE_H_
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