Question

Consider the following MIPS code (don't worry about what it does): loop: beq $s0, $s1, done addi $t0, $t0, 7 addi St1, St2, 4 addi $s0, $s0, 1 j loop done: beq St1, $15, skip addi St0, Sto, 1 addi St1, St2, St0 skip addi $t5, $0, 10 beq St1, St5, done j end Compute the branch offset for each beq in number of words away from the branch (e.g., "branch offset is 2") Assume label loop is at location 0 times 00114214 and label end is at location 0 times 00032794. Compute the correct value to place in the jump address field for each jump instruction in the MIPS code above

Answer 1

A conditional jump is called a branch in MIPS. The offset is a 16-bit value. It can be computed as follows:

Offset = target instruction - (branch instruction + 1).

Now let us number each instruction starting form 0 as follows.

0 loop: beq $s0, $s1, done

1. ….
2. done: beq $t0, $t1, skip
3. skip: addi ….
4. beq $t1, $t5, done
5. jend

offset of instruction 0 = 5 – (0 + 1) = 4

offset of instruction 5 = 8 – (5 + 1) = 2

offset of instruction 9 = 5 – (9 + 1) = 5