Function Shorten

3party/open-location-code/openlocationcode.cc:256–287

}

std::string Shorten(const std::string &code, const LatLng &reference_location) {
  if (!IsFull(code)) {
    return code;
  }
  if (code.find(internal::kPaddingCharacter) != std::string::npos) {
    return code;
  }
  CodeArea code_area = Decode(code);
  LatLng center = code_area.GetCenter();
  // Ensure that latitude and longitude are valid.
  double latitude =
      adjust_latitude(reference_location.latitude, CodeLength(code));
  double longitude = normalize_longitude(reference_location.longitude);
  // How close are the latitude and longitude to the code center.
  double range = std::max(fabs(center.latitude - latitude),
                          fabs(center.longitude - longitude));
  std::string code_copy(code);
  const double safety_factor = 0.3;
  const int removal_lengths[3] = {8, 6, 4};
  for (int removal_length : removal_lengths) {
    // Check if we're close enough to shorten. The range must be less than 1/2
    // the resolution to shorten at all, and we want to allow some safety, so
    // use 0.3 instead of 0.5 as a multiplier.
    double area_edge =
        compute_precision_for_length(removal_length) * safety_factor;
    if (range < area_edge) {
      code_copy = code_copy.substr(removal_length);
      break;
    }
  }
  return code_copy;
}

std::string RecoverNearest(const std::string &short_code,
                           const LatLng &reference_location) {