In addition, because a register of finite length has a finite number of possible states, it must eventually enter a repeating cycle. The initial value of the LFSR is called the seed, and because the operation of the register is deterministic, the stream of output value it produces is completely determined by its current (or previous) state. An LFSR is most often a shift register where the input bit is driven by the exclusive-or (XOR) of certain bits of the contents of the overall shift register. The XOR function can also be viewed as part of the digital addition function in that XORs are used as the Sum portion of the simplest form of the half adder. In digital signal processing, a linear-feedback shift register, or LFSR, is a shift register where the input bit is a linear function of its previous state.Ī common linear function of single bits is the XOR.
