function is_known_ip($ip) { // updated: 2025-04-04  
  // Convert IP string to number
  if (is_string($ip)) {
    $bytes = explode('.', $ip);
    $ip = 0;
    foreach ($bytes as $n) {
      $ip <<= 8;
      $ip |= (int)$n;
    }
  }
  // Check rules
  switch ($ip & 0b0_11111111_11111111_11110000_00000000) { // mask: 255.255.240.0
    case        0b0_11000001_00101011_11000000_00000000:   // ip:   193.43.192.0
      return true;
  }
  switch ($ip & 0b0_11111111_11111111_11111111_00000000) { // mask: 255.255.255.0
    case        0b0_10111100_11010010_11101111_00000000:   // ip:   188.210.239.0
      return true;
  }
  switch ($ip & 0b0_11111111_11111111_11111111_11100000) { // mask: 255.255.255.224
    case        0b0_01001110_00000110_01000011_10000000:   // ip:   78.6.67.128
      return true;
  }
  switch ($ip & 0b0_11111111_11111111_11111111_11111000) { // mask: 255.255.255.248
    case        0b0_01001110_00000101_01001101_01100000:   // ip:   78.5.77.96
      return true;
  }
  switch ($ip & 0b0_11111111_11111111_11111111_11111111) { // mask: 255.255.255.255
    case        0b0_11010100_01001101_01011111_00100011:   // ip:   212.77.95.35
      return true;
  }
  return false;
}