ip2location.go
func readuint128(pos uint32) *big.Int {
	pos2 := int64(pos)
	retval := big.NewInt(0)
	data := make([]byte, 16)
	_, err := f.ReadAt(data, pos2 - 1)
	if err != nil {
		fmt.Println("File read failed:", err)
	}
	
	// little endian to big endian
	for i, j := 0, len(data)-1; i < j; i, j = i+1, j-1 {
		data[i], data[j] = data[j], data[i]
	}
	retval.SetBytes(data)
	return retval
}
func readuint128(pos uint32) *big.Int {
	pos2 := int64(pos)
	retval := big.NewInt(0)
	data := make([]byte, 16)
	_, err := f.ReadAt(data, pos2 - 1)
	if err != nil {
		fmt.Println("File read failed:", err)
	}
	
	// little endian to big endian
	for i, j := 0, len(data)-1; i < j; i, j = i+1, j-1 {
		data[i], data[j] = data[j], data[i]
	}
	retval.SetBytes(data)
	return retval
}
// read unsigned 128-bit integer