Save array from previous iteration into shift register. Detect change - it will give you position.
Angular encoders usually have 90 degrees phase shift between 2 channels. So if value change is positive (rising slope) on one channel and second channel is 1, then it is rotating clockwise. Similar with other 3 cases. Look at your signals with 2 channel scope (or at LabVIEW chart) to check it is the case for your encoder. Arrays are small it will not take time to process them, it can be done on the fly.
