void setup()
{
  Serial.begin(9600);
	
  char buf[64];
  
  unsigned long currentTime = 0x00000100;
  unsigned long earlierTime = 0xFFFFFF00;
    
  unsigned long result = currentTime-earlierTime;
    
  sprintf(buf, "%lx", result);

  Serial.println(buf);
  Serial.println(result, HEX);
}

void loop()
{

}