In Figure 11.11, it is assumed that an array of 80 64-bit words is available to store the values of W_t so that they can be precomputed at the beginning of the processing of a block. Now assume that space is at a premium. As an alternative, consider the use of a 16-word circular buffer that is initially loaded with W₀ through W₁₅. Design an algorithm that, for each step , computes the required input value W_t.