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// pdt.h
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// Copyright 2005-2010 Google, Inc.
// Author: (Michael Riley)
// \file
// Common classes for PDT expansion/traversal.
#include <unordered_map>
using std::tr1::unordered_map;
using std::tr1::unordered_multimap;
#include <map>
#include <set>
#include <fst/state-table.h>
#include <fst/fst.h>
namespace fst {
// Provides bijection between parenthesis stacks and signed integral
// stack IDs. Each stack ID is unique to each distinct stack. The
// open-close parenthesis label pairs are passed in 'parens'.
template <typename K, typename L>
class PdtStack {
typedef K StackId;
typedef L Label;
// The stacks are stored in a tree. The nodes are stored in vector
// 'nodes_'. Each node represents the top of some stack and is
// ID'ed by its position in the vector. Its parent node represents
// the stack with the top 'popped' and its children are stored in
// 'child_map_' accessed by stack_id and label. The paren_id is
// the position in 'parens' of the parenthesis for that node.
struct StackNode {
StackId parent_id;
size_t paren_id;
StackNode(StackId p, size_t i) : parent_id(p), paren_id(i) {}
PdtStack(const vector<pair<Label, Label> > &parens)
: parens_(parens), min_paren_(kNoLabel), max_paren_(kNoLabel) {
for (size_t i = 0; i < parens.size(); ++i) {
const pair<Label, Label> &p = parens[i];
paren_map_[p.first] = i;
paren_map_[p.second] = i;
if (min_paren_ == kNoLabel || p.first < min_paren_)
min_paren_ = p.first;
if (p.second < min_paren_)
min_paren_ = p.second;
if (max_paren_ == kNoLabel || p.first > max_paren_)
max_paren_ = p.first;
if (p.second > max_paren_)
max_paren_ = p.second;
nodes_.push_back(StackNode(-1, -1)); // Tree root.
// Returns stack ID given the current stack ID (0 if empty) and
// label read. 'Pushes' onto a stack if the label is an open
// parenthesis, returning the new stack ID. 'Pops' the stack if the
// label is a close parenthesis that matches the top of the stack,
// returning the parent stack ID. Returns -1 if label is an
// unmatched close parenthesis. Otherwise, returns the current stack
// ID.
StackId Find(StackId stack_id, Label label) {
if (min_paren_ == kNoLabel || label < min_paren_ || label > max_paren_)
return stack_id; // Non-paren.
typename unordered_map<Label, size_t>::const_iterator pit
= paren_map_.find(label);
if (pit == paren_map_.end()) // Non-paren.
return stack_id;
ssize_t paren_id = pit->second;
if (label == parens_[paren_id].first) { // Open paren.
StackId &child_id = child_map_[make_pair(stack_id, label)];
if (child_id == 0) { // Child not found, push label.
child_id = nodes_.size();
nodes_.push_back(StackNode(stack_id, paren_id));
return child_id;
const StackNode &node = nodes_[stack_id];
if (paren_id == node.paren_id) // Matching close paren.
return node.parent_id;
return -1; // Non-matching close paren.
// Returns the stack ID obtained by "popping" the label at the top
// of the current stack ID.
StackId Pop(StackId stack_id) const {
return nodes_[stack_id].parent_id;
// Returns the paren ID at the top of the stack for 'stack_id'
ssize_t Top(StackId stack_id) const {
return nodes_[stack_id].paren_id;
ssize_t ParenId(Label label) const {
typename unordered_map<Label, size_t>::const_iterator pit
= paren_map_.find(label);
if (pit == paren_map_.end()) // Non-paren.
return -1;
return pit->second;
struct ChildHash {
size_t operator()(const pair<StackId, Label> &p) const {
return p.first + p.second * kPrime;
static const size_t kPrime;
vector<pair<Label, Label> > parens_;
vector<StackNode> nodes_;
unordered_map<Label, size_t> paren_map_;
unordered_map<pair<StackId, Label>,
StackId, ChildHash> child_map_; // Child of stack node wrt label
Label min_paren_; // For faster paren. check
Label max_paren_; // For faster paren. check
template <typename T, typename L>
const size_t PdtStack<T, L>::kPrime = 7853;
// State tuple for PDT expansion
template <typename S, typename K>
struct PdtStateTuple {
typedef S StateId;
typedef K StackId;
StateId state_id;
StackId stack_id;
: state_id(kNoStateId), stack_id(-1) {}
PdtStateTuple(StateId fs, StackId ss)
: state_id(fs), stack_id(ss) {}
// Equality of PDT state tuples.
template <typename S, typename K>
inline bool operator==(const PdtStateTuple<S, K>& x,
const PdtStateTuple<S, K>& y) {
if (&x == &y)
return true;
return x.state_id == y.state_id && x.stack_id == y.stack_id;
// Hash function object for PDT state tuples
template <class T>
class PdtStateHash {
size_t operator()(const T &tuple) const {
return tuple.state_id + tuple.stack_id * kPrime;
static const size_t kPrime;
template <typename T>
const size_t PdtStateHash<T>::kPrime = 7853;
// Tuple to PDT state bijection.
template <class S, class K>
class PdtStateTable
: public CompactHashStateTable<PdtStateTuple<S, K>,
PdtStateHash<PdtStateTuple<S, K> > > {
typedef S StateId;
typedef K StackId;
PdtStateTable() {}
PdtStateTable(const PdtStateTable<S, K> &table) {}
void operator=(const PdtStateTable<S, K> &table); // disallow
} // namespace fst