Assume that r0 holds the least significant 32 bits of a 64-bit integer a, and r1 holds the most significant 32 bits of a. Likewise, r2 holds the least significant 32 bits of a 64-bit integer b, and r3 holds the most significant 32 bits of b. Show the shortest instruction sequences necessary to: (a) compare a to b, setting the CPSR flags, (b) shift a left by one bit, storing the result in b, (c) add b to a, and (d) subtract b from a