a. What does the following program do (give a description in English sentences)?

xor $1, $1, $2 xor $2, $1, $2 xor $1, $1, $2

b. Assume that variables a, b, c, and d are mapped to registers $s0, $s1, $s2, and $s3, respectively. Write a MIPS program that implements = ( + ) 7 % 4 using only add, sub, addi, and, andi, or, ori, sll, and srl instructions. Since b, c, and d must not be overwritten, use as many temporary registers ($t0-$t9) as needed.