Write a VHDL module for an 8-bit accumulator for subtraction, which can also shift the accumulator bits to the right. There are two control inputs, A and B. If A = B = 1, the value of the data inputs D are subtracted from the accumulator. If A = 1 and B = o, the value of the data inputs D are loaded directly into the register. If A = o and B = 1, the accumulator should shift right with zero fill. If A = B = o, the accumulator should hold its state. Use an overloaded "-"operator for subtraction.