Lab 5: Branches, Memory, and Arrays in MIPS Assembly

Due Thursday, July 6 at 11:59 PM

Goals for This Lab

By the time you have completed this work, you should be able to:

• Execute instructions conditionally
• Translate conditionals (if/else) and loops (while, for) into MIPS assembly
• Access values in memory with the lw instruction
• Store values in memory with the sw instruction
• Iterate over arrays in memory

• factorial.asm
• sum.asm
• add_amount.asm
• collaborators.txt

Step-by-Step Instructions

Step 1: Edit factorial.asm

Open the factorial.asm file with a text editor of your choice. Note that word processors (e.g., Microsoft Word, Pages, Google Docs) will probably not work for this purpose, as you must save your file as plain text. You must write MIPS assembly code which, when run under QtSpim, will do the following:

1. Read an integer from the user
2. Compute the factorial of the integer
3. Print out the factorial

An example interaction with this program is shown below:

5
120

factorial.asm contains comments which further explain how you can do this. You may assume that the input integer will be non-negative. You may also assume that the computed factorial will fit into a 32-bit unsigned value, so you never need to look at the HI register. The Week 5 Materials have some examples which may be helpful.

Step 2: Edit sum.asm

Now move to the sum.asm file. This program contains a hard-coded array, along with its length, in the .data section of the file. You must iterate through this array, compute the sum of all the elements (i.e., add them all together), and print out the result. Given the existing data in the file, this program should print 28. Your code should work for ANY array and array_length values, but you may assume the following:

• array_length will always be at least 1, and will be an unsigned integer
• array will contain exactly as many .words as array_length.
• Each element of the array will be non-negative

Further details are provided in the comments of sum.asm. The Week 5 Materials have some examples which may be helpful.

Step 3: Edit add_amount.asm

Now move to add_amount.asm. This program works with two arrays of the same length: an input array, and an output array. Additionally, it contains a value to add to each element of the array (amount_to_add). For each element of the input array, it should add this amount, putting the result in the output array. A code snippet below illustrates this behavior:

for (int index = 0; index < array_length; index++) {
  output_array[index] = input_array[index] + amount_to_add;
}

The end of the code (provided) will print each element of the output array. As with the prior problem, this code MUST work for any values of amount_to_add, array_length, input_array, and output_array. You may make the following assumptions in your code:

• array_length will always be at least 1, and will be an unsigned integer
• input_array and output_array will always contain exactly array_length .words.
• The values of input_array will all be non-negative.
• amount_to_add will always be an unsigned integer.

The Week 5 Materials have some examples which may be helpful.

Step 4: Turn in Your Code Using Canvas

Log into Canvas, and go to the COMP 122 class. Click “Assignments” on the left pane, then click “Lab 5”. From here, you can upload your .asm files. Specifically, you must turn in the following three files:

• factorial.asm
• sum.asm
• add_amount.asm

In addition, if you collaborated with anyone else, be sure to download collaborators.txt and write the names of the people you collaborated with in the file, one per line. Please submit this file along with the other three files.

You can turn in the assignment multiple times, but only the last version you submitted will be graded.

IMPORTANT: Your Code Must Run Under QtSpim

The code you submit must run under QtSpim without modification.
Code with syntax errors gets an automatic 0.
If you can't get your code to do the right thing, it's better to submit code that runs but does the wrong thing.