utf8.cpp

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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>.
 */
 
#include "../stdafx.h"
#include "utf8.hpp"
#include "../safeguards.h"
 
[[nodiscard]] std::pair<char[4], size_t> EncodeUtf8(char32_t c)
{
  std::pair<char[4], size_t> result{};
  auto &[buf, len] = result;
  if (c < 0x80) {
    buf[len++] = c;
  } else if (c < 0x800) {
    buf[len++] = 0xC0 + GB(c,  6, 5);
    buf[len++] = 0x80 + GB(c,  0, 6);
  } else if (c < 0x10000) {
    buf[len++] = 0xE0 + GB(c, 12, 4);
    buf[len++] = 0x80 + GB(c,  6, 6);
    buf[len++] = 0x80 + GB(c,  0, 6);
  } else if (c < 0x110000) {
    buf[len++] = 0xF0 + GB(c, 18, 3);
    buf[len++] = 0x80 + GB(c, 12, 6);
    buf[len++] = 0x80 + GB(c,  6, 6);
    buf[len++] = 0x80 + GB(c,  0, 6);
  }
  return result;
}
 
[[nodiscard]] std::pair<size_t, char32_t> DecodeUtf8(std::string_view buf)
{
  if (buf.size() >= 1 && !HasBit(buf[0], 7)) {
    /* Single byte character: 0xxxxxxx */
    char32_t c = buf[0];
    return {1, c};
  } else if (buf.size() >= 2 && GB(buf[0], 5, 3) == 6) {
    if (IsUtf8Part(buf[1])) {
      /* Double byte character: 110xxxxx 10xxxxxx */
      char32_t c = GB(buf[0], 0, 5) << 6 | GB(buf[1], 0, 6);
      if (c >= 0x80) return {2, c};
    }
  } else if (buf.size() >= 3 && GB(buf[0], 4, 4) == 14) {
    if (IsUtf8Part(buf[1]) && IsUtf8Part(buf[2])) {
      /* Triple byte character: 1110xxxx 10xxxxxx 10xxxxxx */
      char32_t c = GB(buf[0], 0, 4) << 12 | GB(buf[1], 0, 6) << 6 | GB(buf[2], 0, 6);
      if (c >= 0x800) return {3, c};
    }
  } else if (buf.size() >= 4 && GB(buf[0], 3, 5) == 30) {
    if (IsUtf8Part(buf[1]) && IsUtf8Part(buf[2]) && IsUtf8Part(buf[3])) {
      /* 4 byte character: 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx */
      char32_t c = GB(buf[0], 0, 3) << 18 | GB(buf[1], 0, 6) << 12 | GB(buf[2], 0, 6) << 6 | GB(buf[3], 0, 6);
      if (c >= 0x10000 && c <= 0x10FFFF) return {4, c};
    }
  }
  return {};
}
 
Utf8View::iterator Utf8View::GetIterAtByte(size_t offset) const
{
  assert(offset <= this->src.size());
  if (offset >= this->src.size()) return this->end();
 
  /* Sanitize iterator to point to the start of a codepoint */
  auto it = iterator(this->src, offset + 1);
  --it;
  return it;
}