int potPin = A0;
float potVal;
int potMap;

void setup() {
  DDRD |= B11111111;
}

void loop() {
  potVal = analogRead(potPin);
  potMap = map(potVal, 0, 1024, 0, 8);
  PIND |= B00000000;
  PORTD |= B00000001 << potMap;
  PORTD &= B01111111 >> potMap;
}