We address the problem of formally verifying arithmetic instructions of microprocessors implemented by microprograms that contain loops. We try to avoid theorem proving techniques using a new symbolic representation: Binary Moment Diagrams (*BMDs). In order to use *BMDs for verifying sequential circuits as well as microprograms, we extend this representation and define several bit-vector level operators. This extension is then integrated into an automatic verification system. We illustrate the paper with examples and we discuss power and weakness of *BMDs.