code: def complex_mult(A, B, shifts, start):
      
  
      alen = len(A)
      blen = len(B)
      areg = pyrtl.Register(alen)
      breg = pyrtl.Register(alen + blen)
      accum = pyrtl.Register(alen + blen)
      done = (areg == 0)  # Multiplication is finished when a becomes 0
      if (shifts > alen) or (shifts > blen):
          raise pyrtl.PyrtlError("shift is larger than one or both of the parameters A or B,"
                                 "please choose smaller shift")
  
      # During multiplication, shift a right every cycle 'shift' times,
      # shift b left every cycle 'shift' times
      with pyrtl.conditional_assignment:
          with start:  # initialization
              areg.next |= A
              breg.next |= B
              accum.next |= 0
  
          with ~done:  # don't run when there's no work to do
              # "Multiply" shifted breg by LSB of areg by cond. adding
              areg.next |= libutils._shifted_reg_next(areg, 'r', shifts)  # right shift
              breg.next |= libutils._shifted_reg_next(breg, 'l', shifts)  # left shift
              accum.next |= accum + _one_cycle_mult(areg, breg, shifts)
  
      return accum, done
docs: Generate shift-and-add multiplier that can shift and add multiple bits per clock cycle.
      Uses substantially more space than `simple_mult()` but is much faster.
  
      :param WireVector A, B: two input wires for the multiplication
      :param int shifts: number of spaces Register is to be shifted per clk cycle
          (cannot be greater than the length of `A` or `B`)
      :param bool start: start signal
      :returns: Register containing the product; the "done" signal