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// 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: (Jeffrey Sorensen)
#include <vector>
using std::vector;
#include <string>
#include <unordered_set>
using std::tr1::unordered_set;
using std::tr1::unordered_multiset;
#include <fst/fst.h>
#include <fst/symbol-table.h>
namespace fst {
// Returns a minimal symbol table containing only symbols referenced by the
// passed fst. Symbols preserve their original numbering, so fst does not
// require relabeling.
template<class Arc>
SymbolTable *PruneSymbolTable(const Fst<Arc> &fst, const SymbolTable &syms,
bool input) {
unordered_set<typename Arc::Label> seen;
seen.insert(0); // Always keep epslion
StateIterator<Fst<Arc> > siter(fst);
for (; !siter.Done(); siter.Next()) {
ArcIterator<Fst<Arc> > aiter(fst, siter.Value());
for (; !aiter.Done(); aiter.Next()) {
typename Arc::Label sym = (input) ? aiter.Value().ilabel :
SymbolTable *pruned = new SymbolTable(syms.Name() + "_pruned");
for (SymbolTableIterator stiter(syms); !stiter.Done(); stiter.Next()) {
typename Arc::Label label = stiter.Value();
if (seen.find(label) != seen.end()) {
pruned->AddSymbol(stiter.Symbol(), stiter.Value());
return pruned;
// Relabels a symbol table to make it a contiguous mapping.
SymbolTable *CompactSymbolTable(const SymbolTable &syms);
// Merges two SymbolTables, all symbols from left will be merged into right
// with the same ids. Symbols in right that have conflicting ids with those
// in left will be assigned to value assigned from the left SymbolTable.
// The returned symbol table will never modify symbol assignments from the left
// side, but may do so on the right. If right_relabel_output is non-NULL, it
// will be assigned true if the symbols from the right table needed to be
// reassigned.
// A potential use case is to Compose two Fst's that have different symbol
// tables. You can reconcile them in the following way:
// Fst<Arc> a, b;
// bool relabel;
// SymbolTable *bnew = MergeSymbolTable(a.OutputSymbols(),
// b.InputSymbols(), &relabel);
// if (relabel) {
// Relabel(b, bnew, NULL);
// }
// b.SetInputSymbols(bnew);
// delete bnew;
SymbolTable *MergeSymbolTable(const SymbolTable &left, const SymbolTable &right,
bool *right_relabel_output = 0);
// Read the symbol table from any Fst::Read()able file, without loading the
// corresponding Fst. Returns NULL if the Fst does not contain a symbol table
// or the symbol table cannot be read.
SymbolTable *FstReadSymbols(const string &filename, bool input);
} // namespace fst