Function Encode

3party/open-location-code/openlocationcode.cc:122–187

}  // anonymous namespace

std::string Encode(const LatLng &location, size_t code_length) {
  // Limit the maximum number of digits in the code.
  code_length = std::min(code_length, internal::kMaximumDigitCount);
  // Adjust latitude and longitude so that they are normalized/clipped.
  double latitude = adjust_latitude(location.latitude, code_length);
  double longitude = normalize_longitude(location.longitude);
  // Reserve 15 characters for the code digits. The separator will be inserted
  // at the end.
  std::string code = "123456789abcdef";

  // Compute the code.
  // This approach converts each value to an integer after multiplying it by
  // the final precision. This allows us to use only integer operations, so
  // avoiding any accumulation of floating point representation errors.

  // Multiply values by their precision and convert to positive without any
  // floating point operations.
  int64_t lat_val =
      internal::kLatitudeMaxDegrees * internal::kGridLatPrecisionInverse;
  int64_t lng_val =
      internal::kLongitudeMaxDegrees * internal::kGridLngPrecisionInverse;
  lat_val += latitude * internal::kGridLatPrecisionInverse;
  lng_val += longitude * internal::kGridLngPrecisionInverse;

  size_t pos = internal::kMaximumDigitCount - 1;
  // Compute the grid part of the code if necessary.
  if (code_length > internal::kPairCodeLength) {
    for (size_t i = 0; i < internal::kGridCodeLength; i++) {
      int lat_digit = lat_val % internal::kGridRows;
      int lng_digit = lng_val % internal::kGridColumns;
      int ndx = lat_digit * internal::kGridColumns + lng_digit;
      code.replace(pos--, 1, 1, internal::kAlphabet[ndx]);
      // Note! Integer division.
      lat_val /= internal::kGridRows;
      lng_val /= internal::kGridColumns;
    }
  } else {
    lat_val /= pow(internal::kGridRows, internal::kGridCodeLength);
    lng_val /= pow(internal::kGridColumns, internal::kGridCodeLength);
  }
  pos = internal::kPairCodeLength - 1;
  // Compute the pair section of the code.
  for (size_t i = 0; i < internal::kPairCodeLength / 2; i++) {
    int lat_ndx = lat_val % internal::kEncodingBase;
    int lng_ndx = lng_val % internal::kEncodingBase;
    code.replace(pos--, 1, 1, internal::kAlphabet[lng_ndx]);
    code.replace(pos--, 1, 1, internal::kAlphabet[lat_ndx]);
    // Note! Integer division.
    lat_val /= internal::kEncodingBase;
    lng_val /= internal::kEncodingBase;
  }

  // Add the separator character.
  code.insert(internal::kSeparatorPosition, &(internal::kSeparator), 1);

  // If we don't need to pad the code, return the requested section.
  if (code_length >= internal::kSeparatorPosition) {
    return code.substr(0, code_length + 1);