bool rechts = LOW;

void setup() {
  // put your setup code here, to run once:
  DDRD=B11111111;
  PORTD=B00000001;
}

void loop() {
  // put your main code here, to run repeatedly:
  delay(500);

  if(PORTD==B10000000){
    rechts = HIGH;
  }
  if(PORTD==B00000001){
    rechts = LOW;
  }
  if(rechts){
     PORTD=PORTD >> 1;
  }
  if(rechts==LOW){
    PORTD=PORTD << 1;
  }
}