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 // Licensed to the Apache Software Foundation (ASF) under one
 // or more contributor license agreements.  See the NOTICE file
 // distributed with this work for additional information
 // regarding copyright ownership.  The ASF licenses this file
 // to you 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.
 
 #pragma once
 
 #include <cassert>
 #include <cstdint>
 #include <cstring>
 #include <iosfwd>
 #include <limits>
 #include <string>
 #include <string_view>
 #include <utility>
 #include <vector>
 
 #include "arrow/status.h"
 #include "arrow/util/macros.h"
 #include "arrow/util/visibility.h"
 
 namespace arrow {
 namespace internal {
 
 // A non-zero-terminated small string class.
 // std::string usually has a small string optimization
 // (see review at https://shaharmike.com/cpp/std-string/)
 // but this one allows tight control and optimization of memory layout.
 template <uint8_t N>
 class SmallString {
  public:
   SmallString() : length_(0) {}
 
   template <typename T>
   SmallString(const T& v) {  // NOLINT implicit constructor
     *this = std::string_view(v);
   }
 
   SmallString& operator=(const std::string_view s) {
 #ifndef NDEBUG
     CheckSize(s.size());
 #endif
     length_ = static_cast<uint8_t>(s.size());
     std::memcpy(data_, s.data(), length_);
     return *this;
   }
 
   SmallString& operator=(const std::string& s) {
     *this = std::string_view(s);
     return *this;
   }
 
   SmallString& operator=(const char* s) {
     *this = std::string_view(s);
     return *this;
   }
 
   explicit operator std::string_view() const { return std::string_view(data_, length_); }
 
   const char* data() const { return data_; }
   size_t length() const { return length_; }
   bool empty() const { return length_ == 0; }
   char operator[](size_t pos) const {
 #ifdef NDEBUG
     assert(pos <= length_);
 #endif
     return data_[pos];
   }
 
   SmallString substr(size_t pos) const {
     return SmallString(std::string_view(*this).substr(pos));
   }
 
   SmallString substr(size_t pos, size_t count) const {
     return SmallString(std::string_view(*this).substr(pos, count));
   }
 
   template <typename T>
   bool operator==(T&& other) const {
     return std::string_view(*this) == std::string_view(std::forward<T>(other));
   }
 
   template <typename T>
   bool operator!=(T&& other) const {
     return std::string_view(*this) != std::string_view(std::forward<T>(other));
   }
 
  protected:
   uint8_t length_;
   char data_[N];
 
   void CheckSize(size_t n) { assert(n <= N); }
 };
 
 template <uint8_t N>
 std::ostream& operator<<(std::ostream& os, const SmallString<N>& str) {
   return os << std::string_view(str);
 }
 
 // A trie class for byte strings, optimized for small sets of short strings.
 // This class is immutable by design, use a TrieBuilder to construct it.
 class ARROW_EXPORT Trie {
   using index_type = int16_t;
   using fast_index_type = int_fast16_t;
   static constexpr auto kMaxIndex = std::numeric_limits<index_type>::max();
 
  public:
   Trie() : size_(0) {}
   Trie(Trie&&) = default;
   Trie& operator=(Trie&&) = default;
 
   int32_t Find(std::string_view s) const {
     const Node* node = &nodes_[0];
     fast_index_type pos = 0;
     if (s.length() > static_cast<size_t>(kMaxIndex)) {
       return -1;
     }
     fast_index_type remaining = static_cast<fast_index_type>(s.length());
 
     while (remaining > 0) {
       auto substring_length = node->substring_length();
       if (substring_length > 0) {
         auto substring_data = node->substring_data();
         if (remaining < substring_length) {
           // Input too short
           return -1;
         }
         for (fast_index_type i = 0; i < substring_length; ++i) {
           if (s[pos++] != substring_data[i]) {
             // Mismatching substring
             return -1;
           }
           --remaining;
         }
         if (remaining == 0) {
           // Matched node exactly
           return node->found_index_;
         }
       }
       // Lookup child using next input character
       if (node->child_lookup_ == -1) {
         // Input too long
         return -1;
       }
       auto c = static_cast<uint8_t>(s[pos++]);
       --remaining;
       auto child_index = lookup_table_[node->child_lookup_ * 256 + c];
       if (child_index == -1) {
         // Child not found
         return -1;
       }
       node = &nodes_[child_index];
     }
 
     // Input exhausted
     if (node->substring_.empty()) {
       // Matched node exactly
       return node->found_index_;
     } else {
       return -1;
     }
   }
 
   Status Validate() const;
 
   void Dump() const;
 
  protected:
   static constexpr size_t kNodeSize = 16;
   static constexpr auto kMaxSubstringLength =
       kNodeSize - 2 * sizeof(index_type) - sizeof(int8_t);
 
   struct Node {
     // If this node is a valid end of string, index of found string, otherwise -1
     index_type found_index_;
     // Base index for child lookup in lookup_table_ (-1 if no child nodes)
     index_type child_lookup_;
     // The substring for this node.
     SmallString<kMaxSubstringLength> substring_;
 
     fast_index_type substring_length() const {
       return static_cast<fast_index_type>(substring_.length());
     }
     const char* substring_data() const { return substring_.data(); }
   };
 
   static_assert(sizeof(Node) == kNodeSize, "Unexpected node size");
 
   ARROW_DISALLOW_COPY_AND_ASSIGN(Trie);
 
   void Dump(const Node* node, const std::string& indent) const;
 
   // Node table: entry 0 is the root node
   std::vector<Node> nodes_;
 
   // Indexed lookup structure: gives index in node table, or -1 if not found
   std::vector<index_type> lookup_table_;
 
   // Number of entries
   index_type size_;
 
   friend class TrieBuilder;
 };
 
 class ARROW_EXPORT TrieBuilder {
   using index_type = Trie::index_type;
   using fast_index_type = Trie::fast_index_type;
 
  public:
   TrieBuilder();
   Status Append(std::string_view s, bool allow_duplicate = false);
   Trie Finish();
 
  protected:
   // Extend the lookup table by 256 entries, return the index of the new span
   Status ExtendLookupTable(index_type* out_lookup_index);
   // Split the node given by the index at the substring index `split_at`
   Status SplitNode(fast_index_type node_index, fast_index_type split_at);
   // Append an already constructed child node to the parent
   Status AppendChildNode(Trie::Node* parent, uint8_t ch, Trie::Node&& node);
   // Create a matching child node from this parent
   Status CreateChildNode(Trie::Node* parent, uint8_t ch, std::string_view substring);
   Status CreateChildNode(Trie::Node* parent, char ch, std::string_view substring);
 
   Trie trie_;
 
   static constexpr auto kMaxIndex = std::numeric_limits<index_type>::max();
 };
 
 }  // namespace internal
 }  // namespace arrow

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