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/*
* Copyright (C) 2018 The Android Open Source Project
*
* 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 LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_DOUBLE_ARRAY_TRIE_H_
#define LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_DOUBLE_ARRAY_TRIE_H_
#include <functional>
#include <vector>
#include "utils/base/endian.h"
#include "utils/sentencepiece/matcher.h"
#include "utils/strings/stringpiece.h"
namespace libtextclassifier3 {
// A trie node specifies a node in the tree, either an intermediate node or
// a leaf node.
// A leaf node contains the id as an int of the string match. This id is encoded
// in the lower 30 bits, thus the number of distinct ids is 2^30.
// An intermediate node has an associated label and an offset to it's children.
// The label is encoded in the least significant byte and must match the input
// character during matching.
// We account for endianness when using the node values, as they are serialized
// (in little endian) as bytes in the flatbuffer model.
typedef unsigned int TrieNode;
// A memory mappable trie, compatible with Darts::DoubleArray.
class DoubleArrayTrie : public SentencePieceMatcher {
public:
// nodes and nodes_length specify the array of the nodes of the trie.
DoubleArrayTrie(const TrieNode* nodes, const int nodes_length)
: nodes_(nodes), nodes_length_(nodes_length) {}
// Find matches that are prefixes of a string.
bool FindAllPrefixMatches(StringPiece input,
std::vector<TrieMatch>* matches) const override;
// Find the longest prefix match of a string.
bool LongestPrefixMatch(StringPiece input,
TrieMatch* longest_match) const override;
private:
// Returns whether a node as a leaf as a child.
bool has_leaf(unsigned int i) const { return nodes_[i] & 0x100; }
// Available when a node is a leaf.
int value(unsigned int i) const {
return static_cast<int>(LittleEndian::ToHost32(nodes_[i]) & 0x7fffffff);
}
// Label associated with a node.
// A leaf node will have the MSB set and thus return an invalid label.
unsigned int label(unsigned int i) const {
return LittleEndian::ToHost32(nodes_[i]) & 0x800000ff;
}
// Returns offset to children.
unsigned int offset(unsigned int i) const {
const unsigned int node = LittleEndian::ToHost32(nodes_[i]);
return (node >> 10) << ((node & 0x200) >> 6);
}
bool GatherPrefixMatches(
StringPiece input, const std::function<void(TrieMatch)>& update_fn) const;
const TrieNode* nodes_;
const int nodes_length_;
};
} // namespace libtextclassifier3
#endif // LIBTEXTCLASSIFIER_UTILS_SENTENCEPIECE_DOUBLE_ARRAY_TRIE_H_
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