/*
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* Copyright (C) 2018 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_NORMALIZER_H_
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#define LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_NORMALIZER_H_
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#include <memory>
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#include <string>
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#include "utils/sentencepiece/double_array_trie.h"
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#include "utils/strings/stringpiece.h"
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namespace libtextclassifier3 {
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// Normalizer implements a simple text normalizer with user-defined
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// string-to-string rules and leftmost longest matching.
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class SentencePieceNormalizer {
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public:
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// charsmap_trie and charsmap_normalized specify the normalization/replacement
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// string-to-string rules in the following way:
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// A match in the trie for a string will return the offset in
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// charsmap_normalized that contains the replacement string.
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//
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// add_dummy_prefix: Whether to add dummy whitespace at the beginning of the
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// text in order to treat "world" in "world" and "hello world" uniformly.
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//
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// remove_extra_whitespaces: Whether to remove leading, trailing and duplicate
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// internal whitespace.
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//
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// escape_whitespaces: Whether to replace whitespace with a meta symbol.
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SentencePieceNormalizer(const DoubleArrayTrie& charsmap_trie,
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StringPiece charsmap_normalized,
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bool add_dummy_prefix = true,
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bool remove_extra_whitespaces = true,
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bool escape_whitespaces = true)
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: charsmap_trie_(charsmap_trie),
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charsmap_normalized_(charsmap_normalized),
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add_dummy_prefix_(add_dummy_prefix),
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remove_extra_whitespaces_(remove_extra_whitespaces),
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escape_whitespaces_(escape_whitespaces) {}
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// Normalizes a plain utf8 string into an internal representation for
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// Sentencepiece model.
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bool Normalize(StringPiece input, std::string* normalized_input) const;
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private:
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// Normalizes the prefix of `input` and returns the pair of
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// normalized prefix and the length of the prefix of `input` processed in the
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// normalization.
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bool NormalizePrefix(StringPiece input,
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std::pair<StringPiece, int>* prefix) const;
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// Internal trie for efficient longest prefix string matching.
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DoubleArrayTrie charsmap_trie_;
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// "\0" delimitered concatenated normalized strings.
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// the value of `charsmap_trie_` stores offsets into this string.
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StringPiece charsmap_normalized_;
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const bool add_dummy_prefix_;
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const bool remove_extra_whitespaces_;
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const bool escape_whitespaces_;
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};
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} // namespace libtextclassifier3
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#endif // LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_NORMALIZER_H_
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