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// Copyright 2016 Google Inc.
//
// 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://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.!
#ifndef NORMALIZER_NORMALIZER_H_
#define NORMALIZER_NORMALIZER_H_
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include "common.h"
#include "sentencepiece_model.pb.h"
#include "sentencepiece_processor.h"
#include "third_party/absl/strings/string_view.h"
#include "third_party/darts_clone/darts.h"
namespace sentencepiece {
namespace normalizer {
// Normalizer implements a simple text normalizer with
// user-defined string-to-string rules and leftmost longest
// matching. The rules of Normalizer are built with
// Builder::CompileCharsMap() method. Pre-compiled rules are
// also available via Builder::GetPrecompiledCharsMap(<name>) method.
//
// The motivation of Normalizer is to make flexible, user-customizable
// and self-contained normalizer. All the logic of normalization is
// encoded in the model proto which allows us to define language/task
// dependent normalization rules without breaking the default rule.
class Normalizer {
public:
// Instantiates Normalizer with |spec|.
// |spec| should not be deleted until Normalizer is destroyed.
explicit Normalizer(const NormalizerSpec &spec);
virtual ~Normalizer();
// Returns Status.
// Normalizes function is valid only when status is OK.
virtual util::Status status() const { return status_; }
// Normalizes a plain utf8 string into an internal representation for
// Sentencepiece model. |norm_to_orig| stores the byte-alignment from
// normalized string to the original input.
// This function can do the following normalizations:
// - Character normalization.
// (NFKC / full-width to half-width conversion etc).
// - Adds a prefix space.
// - Replaces a space with a meta symbol.
// - Removing heading, tailing and other redundant spaces.
virtual util::Status Normalize(absl::string_view input, std::string *normalized,
std::vector<size_t> *norm_to_orig) const;
// Returns a normalized string without alignments.
// This function is used in sentencepiece training.
virtual std::string Normalize(absl::string_view input) const;
friend class Builder;
private:
FRIEND_TEST(NormalizerTest, EncodeDecodePrecompiledCharsMapTest);
// Normalizes the prefix of |input| and returns the pair of
// normalized prefix and length we must consume after
// normalization.
// Here's the sample code for the full text normalization.
//
// string output;
// absl::string_view input = "...";
// while (!input.empty()) {
// const auto p = normalizer.NormalizePrefix(input);
// output.append(p.first.data(), p.first.size());
// input.remove_prefix(p.second);
// }
std::pair<absl::string_view, int> NormalizePrefix(absl::string_view input) const;
// Encodes trie_blob and normalized string and return compiled blob.
static std::string EncodePrecompiledCharsMap(absl::string_view trie_blob,
absl::string_view normalized);
// Decodes blob into trie_blob and normalized string.
static util::Status DecodePrecompiledCharsMap(absl::string_view blob,
absl::string_view *trie_blob,
absl::string_view *normalized);
// Maximum size of the return value of Trie, which corresponds
// to the maximum size of shared common prefix in the chars map.
static constexpr int kMaxTrieResultsSize = 32;
// Internal trie for efficient longest matching.
std::unique_ptr<Darts::DoubleArray> trie_;
// "\0" delimitered output string.
// the value of |trie_| stores pointers to this string.
const char *normalized_ = nullptr;
// Spec for normalization.
const NormalizerSpec *spec_;
// Normalizer's status.
util::Status status_;
};
} // namespace normalizer
} // namespace sentencepiece
#endif // NORMALIZER_NORMALIZER_H_
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