Circular shifts are sometimes called rotating shifts because they form a kind of circle of bits. The value of a register is not lost if it subjected to a series of circular shifts. In fact, if an n-bit register is circularly shifted n times, it will wind up with the original value. This is not true with logical shifts since bits are constantly getting lost at one end and 0s are inserted at the other. To set an n-bit register to 0, subject it to n logical shifts, either left or right.