After opening with a positive gap of 35 points at 12,388, the index touched a high of 12,390, and then tumbled into the negative zone to touch a low of 12,315 - down 75 points from the day's high.The index has now rebounded into the positive zone and is now up 4 points at 12,357.HDFC has surged 1.8% to Rs 1,465. Dr.Reddy's has spurted 1% to Rs 711.Reliance, ACC and Tata Motors are the other smart gainers.