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label-maker.h
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label-maker.h
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// festus/label-maker.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
//
// http:https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Copyright 2015, 2016 Google, Inc.
// Author: [email protected] (Martin Jansche)
//
// \file
// Conversion between symbols and numeric labels.
#ifndef FESTUS_LABEL_MAKER_H__
#define FESTUS_LABEL_MAKER_H__
#include <vector>
#include <fst/compat.h>
#include <fst/symbol-table.h>
#include "festus/string-util.h"
namespace festus {
// Abstract converter between C++ byte strings and FST label sequences.
class LabelMaker {
public:
typedef std::vector<int> Labels;
virtual ~LabelMaker() = default;
virtual const fst::SymbolTable *Symbols() const { return nullptr; }
virtual bool StringToLabels(const StringPiece str, Labels *labels) const = 0;
virtual bool LabelsToString(const Labels &labels, string *str) const = 0;
template <class CompactFstType>
bool StringToCompactFst(const StringPiece str, CompactFstType *fst) {
Labels labels;
if (!StringToLabels(str, &labels)) return false;
fst->SetCompactElements(labels.begin(), labels.end());
return true;
}
};
// Converter that turns a C++ byte string into an FST label sequence where
// bytes (viewed as unsigned integers) correspond one-for-one to labels.
class ByteLabelMaker : public LabelMaker {
public:
ByteLabelMaker() = default;
bool StringToLabels(const StringPiece str, Labels *labels) const override;
bool LabelsToString(const Labels &labels, string *str) const override;
};
// Converter between UTF-8 byte strings and sequences of Unicode codepoints.
// Strings must be structurally valid UTF-8. Labels represent UTF-32 codepoints.
class UnicodeLabelMaker : public LabelMaker {
public:
UnicodeLabelMaker() = default;
bool StringToLabels(const StringPiece str, Labels *labels) const override;
bool LabelsToString(const Labels &labels, string *str) const override;
};
// Converter that splits a byte string into symbols and looks up the label
// values in the provided symbol table.
class SymbolLabelMaker : public LabelMaker {
public:
// TODO: Add special handling of "" as delimiter.
SymbolLabelMaker(const fst::SymbolTable *symbols, string delimiters);
~SymbolLabelMaker() override;
const fst::SymbolTable *Symbols() const override { return symbols_; }
bool StringToLabels(const StringPiece str, Labels *labels) const override;
bool LabelsToString(const Labels &labels, string *str) const override;
private:
SymbolLabelMaker() = delete;
const fst::SymbolTable *const symbols_;
const string delimiters_;
};
} // namespace festus
#endif // FESTUS_LABEL_MAKER_H__