Answer:

Both operand registers and the result register can all be the same. (This is not true on many processors, but MIPS is nice in this way.)

The effect of adding an integer to itself is doubling it. The maximum unsigned integer that can be represented in 32 bits is +2³²-1 so the maximum that $8 could start with is: +2³¹-1

Example Program

## AddSome.asm
## 
## Program to demonstrate addition
        .text
        .globl  main

main:
        ori      $8, $0, 0xAB       # put 0x000000AB into $8
        ori      $9, $0, 0x55       # put 0x00000055 into $9
        addu     $10,$9, $8         # $10  gets sum

## End of file

Here is the addition problem on a previous page extended to 32 bits.

carry:   0 0000 0000 0000 0000 0000 0001 1111 111
           0000 0000 0000 0000 0000 0000 1010 1011         000000AB
           0000 0000 0000 0000 0000 0000 0101 0101         00000055
           0000 0000 0000 0000 0000 0001 0000 0000         00000100

What was unsigned overflow with 8-bit unsigned arithmetic is within range for 32-bit arithmetic.

QUESTION 5:

Are registers $8 and $9 changed by the addu instruction in this program?