code: func oldBtcdHomeDir() string {
  	// Search for Windows APPDATA first.  This won't exist on POSIX OSes.
  	appData := os.Getenv("APPDATA")
  	if appData != "" {
  		return filepath.Join(appData, "btcd")
  	}
  
  	// Fall back to standard HOME directory that works for most POSIX OSes.
  	home := os.Getenv("HOME")
  	if home != "" {
  		return filepath.Join(home, ".btcd")
  	}
  
  	// In the worst case, use the current directory.
  	return "."
  }
docs: // oldBtcdHomeDir returns the OS specific home directory btcd used prior to
  // version 0.3.3.  This has since been replaced with btcutil.AppDataDir, but
  // this function is still provided for the automatic upgrade path.