utf8.hpp

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/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#ifndef UTF8_HPP
#define UTF8_HPP
 
#include <iterator>
#include "bitmath_func.hpp"
 
[[nodiscard]] std::pair<char[4], size_t> EncodeUtf8(char32_t c);
[[nodiscard]] std::pair<size_t, char32_t> DecodeUtf8(std::string_view buf);
 
/* Check if the given character is part of a UTF8 sequence */
inline bool IsUtf8Part(char c)
{
  return GB(c, 6, 2) == 2;
}

class Utf8View {
  std::string_view src;
public:
  Utf8View() = default;
  Utf8View(std::string_view src) : src(src) {}

  class iterator {
    std::string_view src;
    size_t position = 0;
  public:
    using value_type = char32_t;
    using difference_type = std::ptrdiff_t;
    using iterator_category = std::bidirectional_iterator_tag;
    using pointer = void;
    using reference = void;
 
    iterator() = default;
    iterator(std::string_view src, size_t position) : src(src), position(position) {}
 
    size_t GetByteOffset() const
    {
      return this->position;
    }
 
    bool operator==(const iterator &rhs) const
    {
      assert(this->src.data() == rhs.src.data());
      return this->position == rhs.position;
    }
 
    std::strong_ordering operator<=>(const iterator &rhs) const
    {
      assert(this->src.data() == rhs.src.data());
      return this->position <=> rhs.position;
    }
 
    char32_t operator*() const
    {
      assert(this->position < this->src.size());
      auto [len, c] = DecodeUtf8(this->src.substr(this->position));
      return len > 0 ? c : '?';
    }
 
    iterator& operator++()
    {
      auto size = this->src.size();
      assert(this->position < size);
      do {
        ++this->position;
      } while (this->position < size && IsUtf8Part(this->src[this->position]));
      return *this;
    }
 
    iterator operator++(int)
    {
      iterator result = *this;
      ++*this;
      return result;
    }
 
    iterator& operator--()
    {
      assert(this->position > 0);
      do {
        --this->position;
      } while (this->position > 0 && IsUtf8Part(this->src[this->position]));
      return *this;
    }
 
    iterator operator--(int)
    {
      iterator result = *this;
      --*this;
      return result;
    }
  };
 
  iterator begin() const
  {
    return iterator(this->src, 0);
  }
 
  iterator end() const
  {
    return iterator(this->src, this->src.size());
  }
 
  iterator GetIterAtByte(size_t offset) const;
};
 
#endif /* UTF8_HPP */