created 06/20/2003; edited: 07/24/2015

# Chapter 13 Programming Exercises

For these programming exercises, use only those instructions that have been discussed so far in these notes:

In the Settings menu of SPIM set Bare Machine ON, Allow Pseudo Instructions OFF, Load Trap File OFF, Delayed Branches ON, Delayed Loads ON, Mapped IO OFF, Quiet OFF.

Run the programs by setting the value of the PC to 0x400000 and then single stepping (pushing F10) or by multiple stepping (push F11 and enter a number of steps). Observing the results in the SPIM window.

## *Exercise 1 — Column Addition

Write a program that adds up the following integers:

``` 456
-229
325
-552
```

Leave the answer in register \$8.

## *Exercise 2 — Shifting and Adding

Initialize the sum in register \$8 to zero. Then add 409610 to \$8 sixteen times. You don't know how to loop, yet, so do this by making 16 copies of the same instruction. The value 409610 is 0x1000.

Next initialize register \$9 to 409610. Shift \$9 left by the correct number of positions so that registers \$8 and \$9 contain the same bit pattern.

Finally, initialize aregister \$10 to 409610. Add \$10 to itself the correct number of times so that it contains the same bit pattern as the other two registers.

## *Exercise 3 — Trapping Overflow

Initialize register \$9 to 0x7000. Shift the bit pattern so that \$9 contains 0x70000000. Now use `addu` to add \$9 to itself. Is the result correct?

Now use the `add` instruction and run the program again. What happens?

This may be the only time in this course that you will use the `add` instruction.

## *Exercise 4 — Arithmetic Expression

Let register \$8 be `x` and register \$9 be `y`. Write a program to evaluate:

```3x - 5y
```

Leave the result in register \$10. Inspect the register after running the program to check that the program works. Run the program several times, initialize `x` and `y` to different values for each run.

## **Exercise 5 — Two's Complement

Let register \$8 be `x`. Write a program that computes `13x`. Leave the result in register \$10. Initialize `x` to 1 for debugging. Then try some other positive values.

Extend your program so that it also computes `-13x` and leaves the result in register \$11 (This will take one additional instruction.) Now initialize `x` to -1. Look at your result for `13x`. Is it correct?