code: def MOVSX(cpu, op0, op1):
          
          op0.write(Operators.SEXTEND(op1.read(), op1.size, op0.size))
docs: Moves with sign-extension.
  
          Copies the contents of the source operand (register or memory location) to the destination
          operand (register) and sign extends the value to 16::
  
                  OP0  =  SignExtend(OP1);
  
          :param cpu: current CPU.
          :param op0: destination operand.
          :param op1: source operand.