On some machines, the SHR instruction used in Fig. 9-38(b) fills the unused bits with zeros; on

Question:

On some machines, the SHR instruction used in Fig. 9-38(b) fills the unused bits with zeros; on others the sign bit is extended to the right. For the correctness of Fig. 9-38(b), does it matter which kind of shift instruction is used? If so, which is better?