/usr/include/fst/synchronize.h is in libfst-dev 1.5.3+r3-2.
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// finite-state transducer library.
//
// Synchronize an FST with bounded delay.
#ifndef FST_LIB_SYNCHRONIZE_H_
#define FST_LIB_SYNCHRONIZE_H_
#include <algorithm>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
#include <fst/cache.h>
#include <fst/test-properties.h>
namespace fst {
typedef CacheOptions SynchronizeFstOptions;
// Implementation class for SynchronizeFst
template <class A>
class SynchronizeFstImpl : public CacheImpl<A> {
public:
using FstImpl<A>::SetType;
using FstImpl<A>::SetProperties;
using FstImpl<A>::SetInputSymbols;
using FstImpl<A>::SetOutputSymbols;
using CacheBaseImpl<CacheState<A>>::PushArc;
using CacheBaseImpl<CacheState<A>>::HasArcs;
using CacheBaseImpl<CacheState<A>>::HasFinal;
using CacheBaseImpl<CacheState<A>>::HasStart;
using CacheBaseImpl<CacheState<A>>::SetArcs;
using CacheBaseImpl<CacheState<A>>::SetFinal;
using CacheBaseImpl<CacheState<A>>::SetStart;
typedef A Arc;
typedef typename A::Label Label;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef basic_string<Label> String;
struct Element {
Element() {}
Element(StateId s, const String *i, const String *o)
: state(s), istring(i), ostring(o) {}
StateId state; // Input state Id
const String *istring; // Residual input labels
const String *ostring; // Residual output labels
// Residual strings are represented by const pointers to
// basic_string<Label> and are stored in a hash_set. The pointed
// memory is owned by the hash_set string_set_.
};
SynchronizeFstImpl(const Fst<A> &fst, const SynchronizeFstOptions &opts)
: CacheImpl<A>(opts), fst_(fst.Copy()) {
SetType("synchronize");
uint64 props = fst.Properties(kFstProperties, false);
SetProperties(SynchronizeProperties(props), kCopyProperties);
SetInputSymbols(fst.InputSymbols());
SetOutputSymbols(fst.OutputSymbols());
}
SynchronizeFstImpl(const SynchronizeFstImpl &impl)
: CacheImpl<A>(impl), fst_(impl.fst_->Copy(true)) {
SetType("synchronize");
SetProperties(impl.Properties(), kCopyProperties);
SetInputSymbols(impl.InputSymbols());
SetOutputSymbols(impl.OutputSymbols());
}
~SynchronizeFstImpl() override {
delete fst_;
// Extract pointers from the hash set
std::vector<const String *> strings;
auto it = string_set_.begin();
for (; it != string_set_.end(); ++it) strings.push_back(*it);
// Free the extracted pointers
for (size_t i = 0; i < strings.size(); ++i) delete strings[i];
}
StateId Start() {
if (!HasStart()) {
StateId s = fst_->Start();
if (s == kNoStateId) return kNoStateId;
const String *empty = FindString(new String());
StateId start = FindState(Element(fst_->Start(), empty, empty));
SetStart(start);
}
return CacheImpl<A>::Start();
}
Weight Final(StateId s) {
if (!HasFinal(s)) {
const Element &e = elements_[s];
Weight w = e.state == kNoStateId ? Weight::One() : fst_->Final(e.state);
if ((w != Weight::Zero()) && (e.istring)->empty() && (e.ostring)->empty())
SetFinal(s, w);
else
SetFinal(s, Weight::Zero());
}
return CacheImpl<A>::Final(s);
}
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);
}
uint64 Properties() const override { return Properties(kFstProperties); }
// Set error if found; return FST impl properties.
uint64 Properties(uint64 mask) const override {
if ((mask & kError) && fst_->Properties(kError, false))
SetProperties(kError, kError);
return FstImpl<Arc>::Properties(mask);
}
void InitArcIterator(StateId s, ArcIteratorData<A> *data) {
if (!HasArcs(s)) Expand(s);
CacheImpl<A>::InitArcIterator(s, data);
}
// Returns the first character of the string obtained by
// concatenating s and l.
Label Car(const String *s, Label l = 0) const {
if (!s->empty())
return (*s)[0];
else
return l;
}
// Computes the residual string obtained by removing the first
// character in the concatenation of s and l.
const String *Cdr(const String *s, Label l = 0) {
String *r = new String();
for (int i = 1; i < s->size(); ++i) r->push_back((*s)[i]);
if (l && !(s->empty())) r->push_back(l);
return FindString(r);
}
// Computes the concatenation of s and l.
const String *Concat(const String *s, Label l = 0) {
String *r = new String();
for (int i = 0; i < s->size(); ++i) r->push_back((*s)[i]);
if (l) r->push_back(l);
return FindString(r);
}
// Tests if the concatenation of s and l is empty
bool Empty(const String *s, Label l = 0) const {
if (s->empty())
return l == 0;
else
return false;
}
// Finds the string pointed by s in the hash set. Transfers the
// pointer ownership to the hash set.
const String *FindString(const String *s) {
auto it = string_set_.find(s);
if (it != string_set_.end()) {
delete s;
return (*it);
} else {
string_set_.insert(s);
return s;
}
}
// Finds state corresponding to an element. Creates new state
// if element not found.
StateId FindState(const Element &e) {
auto eit = element_map_.find(e);
if (eit != element_map_.end()) {
return (*eit).second;
} else {
StateId s = elements_.size();
elements_.push_back(e);
element_map_.insert(std::pair<const Element, StateId>(e, s));
return s;
}
}
// Computes the outgoing transitions from a state, creating new destination
// states as needed.
void Expand(StateId s) {
Element e = elements_[s];
if (e.state != kNoStateId)
for (ArcIterator<Fst<A>> ait(*fst_, e.state); !ait.Done(); ait.Next()) {
const A &arc = ait.Value();
if (!Empty(e.istring, arc.ilabel) && !Empty(e.ostring, arc.olabel)) {
const String *istring = Cdr(e.istring, arc.ilabel);
const String *ostring = Cdr(e.ostring, arc.olabel);
StateId d = FindState(Element(arc.nextstate, istring, ostring));
PushArc(s, Arc(Car(e.istring, arc.ilabel), Car(e.ostring, arc.olabel),
arc.weight, d));
} else {
const String *istring = Concat(e.istring, arc.ilabel);
const String *ostring = Concat(e.ostring, arc.olabel);
StateId d = FindState(Element(arc.nextstate, istring, ostring));
PushArc(s, Arc(0, 0, arc.weight, d));
}
}
Weight w = e.state == kNoStateId ? Weight::One() : fst_->Final(e.state);
if ((w != Weight::Zero()) &&
((e.istring)->size() + (e.ostring)->size() > 0)) {
const String *istring = Cdr(e.istring);
const String *ostring = Cdr(e.ostring);
StateId d = FindState(Element(kNoStateId, istring, ostring));
PushArc(s, Arc(Car(e.istring), Car(e.ostring), w, d));
}
SetArcs(s);
}
private:
// Equality function for Elements, assume strings have been hashed.
class ElementEqual {
public:
bool operator()(const Element &x, const Element &y) const {
return x.state == y.state && x.istring == y.istring &&
x.ostring == y.ostring;
}
};
// Hash function for Elements to Fst states.
class ElementKey {
public:
size_t operator()(const Element &x) const {
size_t key = x.state;
key = (key << 1) ^ (x.istring)->size();
for (size_t i = 0; i < (x.istring)->size(); ++i)
key = (key << 1) ^ (*x.istring)[i];
key = (key << 1) ^ (x.ostring)->size();
for (size_t i = 0; i < (x.ostring)->size(); ++i)
key = (key << 1) ^ (*x.ostring)[i];
return key;
}
};
// Equality function for strings
class StringEqual {
public:
bool operator()(const String *const &x, const String *const &y) const {
if (x->size() != y->size()) return false;
for (size_t i = 0; i < x->size(); ++i)
if ((*x)[i] != (*y)[i]) return false;
return true;
}
};
// Hash function for set of strings
class StringKey {
public:
size_t operator()(const String *const &x) const {
size_t key = x->size();
for (size_t i = 0; i < x->size(); ++i) key = (key << 1) ^ (*x)[i];
return key;
}
};
typedef std::unordered_map<Element, StateId, ElementKey, ElementEqual>
ElementMap;
typedef std::unordered_set<const String *, StringKey, StringEqual> StringSet;
const Fst<A> *fst_;
std::vector<Element> elements_; // mapping Fst state to Elements
ElementMap element_map_; // mapping Elements to Fst state
StringSet string_set_;
void operator=(const SynchronizeFstImpl<A> &); // disallow
};
// Synchronizes a transducer. This version is a delayed Fst. The
// result will be an equivalent FST that has the property that during
// the traversal of a path, the delay is either zero or strictly
// increasing, where the delay is the difference between the number of
// non-epsilon output labels and input labels along the path.
//
// For the algorithm to terminate, the input transducer must have
// bounded delay, i.e., the delay of every cycle must be zero.
//
// Complexity:
// - A has bounded delay: exponential
// - A does not have bounded delay: does not terminate
//
// References:
// - Mehryar Mohri. Edit-Distance of Weighted Automata: General
// Definitions and Algorithms, International Journal of Computer
// Science, 14(6): 957-982 (2003).
//
// This class attaches interface to implementation and handles
// reference counting, delegating most methods to ImplToFst.
template <class A>
class SynchronizeFst : public ImplToFst<SynchronizeFstImpl<A>> {
public:
friend class ArcIterator<SynchronizeFst<A>>;
friend class StateIterator<SynchronizeFst<A>>;
typedef A Arc;
typedef typename A::Weight Weight;
typedef typename A::StateId StateId;
typedef DefaultCacheStore<A> Store;
typedef typename Store::State State;
typedef SynchronizeFstImpl<A> Impl;
explicit SynchronizeFst(const Fst<A> &fst)
: ImplToFst<Impl>(std::make_shared<Impl>(fst, SynchronizeFstOptions())) {}
SynchronizeFst(const Fst<A> &fst, const SynchronizeFstOptions &opts)
: ImplToFst<Impl>(std::make_shared<Impl>(fst, opts)) {}
// See Fst<>::Copy() for doc.
SynchronizeFst(const SynchronizeFst<A> &fst, bool safe = false)
: ImplToFst<Impl>(fst, safe) {}
// Get a copy of this SynchronizeFst. See Fst<>::Copy() for further doc.
SynchronizeFst<A> *Copy(bool safe = false) const override {
return new SynchronizeFst<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;
void operator=(const SynchronizeFst<A> &fst); // Disallow
};
// Specialization for SynchronizeFst.
template <class A>
class StateIterator<SynchronizeFst<A>>
: public CacheStateIterator<SynchronizeFst<A>> {
public:
explicit StateIterator(const SynchronizeFst<A> &fst)
: CacheStateIterator<SynchronizeFst<A>>(fst, fst.GetMutableImpl()) {}
};
// Specialization for SynchronizeFst.
template <class A>
class ArcIterator<SynchronizeFst<A>>
: public CacheArcIterator<SynchronizeFst<A>> {
public:
typedef typename A::StateId StateId;
ArcIterator(const SynchronizeFst<A> &fst, StateId s)
: CacheArcIterator<SynchronizeFst<A>>(fst.GetMutableImpl(), s) {
if (!fst.GetImpl()->HasArcs(s)) fst.GetMutableImpl()->Expand(s);
}
private:
DISALLOW_COPY_AND_ASSIGN(ArcIterator);
};
template <class A>
inline void SynchronizeFst<A>::InitStateIterator(
StateIteratorData<A> *data) const {
data->base = new StateIterator<SynchronizeFst<A>>(*this);
}
// Synchronizes a transducer. This version writes the synchronized
// result to a MutableFst. The result will be an equivalent FST that
// has the property that during the traversal of a path, the delay is
// either zero or strictly increasing, where the delay is the
// difference between the number of non-epsilon output labels and
// input labels along the path.
//
// For the algorithm to terminate, the input transducer must have
// bounded delay, i.e., the delay of every cycle must be zero.
//
// Complexity:
// - A has bounded delay: exponential
// - A does not have bounded delay: does not terminate
//
// References:
// - Mehryar Mohri. Edit-Distance of Weighted Automata: General
// Definitions and Algorithms, International Journal of Computer
// Science, 14(6): 957-982 (2003).
template <class Arc>
void Synchronize(const Fst<Arc> &ifst, MutableFst<Arc> *ofst) {
SynchronizeFstOptions opts;
opts.gc_limit = 0; // Cache only the last state for fastest copy.
*ofst = SynchronizeFst<Arc>(ifst, opts);
}
} // namespace fst
#endif // FST_LIB_SYNCHRONIZE_H_
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