CS2110 Project 3- Assembly Solution

1.1 Introduction
Hello and welcome to Project 3. In this project, you’ll write some simple programs in assembly, and then implement bit shifting, the Collatz conjecture problem, and a dot product calculator in assembly!
1.2 General Instructions
• Take a look at Section 8 for details on the LC-3 Assembly Programming requirements that you must adhere to
1.3 Running the autograder
Take a look at section 6 for information on how to run the autograder, and how to debug your code. For this project, we will be using complx in the Docker Container to debug our code.
2 Simple ASM Programs
2.1 Compare
To start off, you will implement the compare function. Comparing two values is something you will do frequently in assembly, so it’s important you know how to do this. The two operands are stored in memory with the labels A and B. You will load them from memory, and store a value in the label RESULT. The value that you store to RESULT depends on whether A is greater than B.
• If A < B, you should store −1.
• If A = B, you should store 0.
• If A > B, you should store 1.
2.2 Modulus
In this part of the project, you will be implementing the modulus operator that you will find in a lot of programming languages. Since there are different interpretations of modulus for negative numbers, you should take the absolute values of both your operands and then perform the operation. The two operands are stored in memory with the labels A and B. You will load them from memory, perform the modulus operation, and then store the result in the label RESULT.
Suggested Pseudocode:

a = mem[A]; b = mem[B];
a = abs(a); b = abs(b);
while (a >= b) { a = a - b;
} mem[RESULT] = a;
2.3 String Manipulation
Next, you will write a program that takes in a string stored in memory, changes any lowercase letters in the string to uppercase letters, and stores this new string back into memory.
• Strings are essentially a contiguous array of ASCII values. In this case, the first character is stored at the address indicated by the value at the address labeled as STRING.
• The string continues until the first instance of a null terminator, which has the value of 0.
Here is an example layout:
Address Label Value
··· ··· ···
x3021 STRING x4000
x3022 RESULT
··· ··· ···
x4000 “h”
x4001 “A”
x4002 “h”
x4003 “A”
x4004 0
3 Bit Shifting
For this section of the product, you will implement bit-shifting in LC3 assembly as subroutines. As such, values for bit shifting will no longer be placed at label values, but rather, passed-in values will now be passed in through registers. Results will also be stored in registers.You will be given an original value, and amount of bits to shift by. Note, for shifting, expected behavior involves adding zero’s from the left and right. We will not be sign-extending.
The operands will be passed in through 2 registers, R0 for the value and R1 for the shift amount. The result should be stored at R0. You will not have to handle overflow. Write your code in collatzconjecture.asm, under the appropriate sections and .orig tags (x3100 for SHIFTLEFT, x3200 for SHIFTRIGHT).
Suggested Pseudocode (Shift Right):

val = R0; amt = R1; result = 0;
while (amt < 16) { result = result + result; if (val < 0) { result++;
}
val = val + val;
amt++;
}
R0 = result;
Suggested Pseudocode (Shift Left):

val = R0; amt = R1;
while (amt > 0) { val += val; amt--;
}
R0 = val;
4 Collatz Conjecture
For this part of the project, you will be implementing a calculator for iterations of the Collatz Conjecture. This program will use labels as input/output, but will be required to call the subroutines shiftleft and shiftright that you wrote previously.
The Collatz Conjecture is a famous unsolved math problem, which operates under a few simple rules. We have our Collatz function, C(n), which takes in exclusively positive integers. If n is an odd number, C(n) = 3n+1. If n is an even number, . From here, we seek to calculate how many times we need to run n (and its subsequent results) through the Collatz function in order for it to reach the value 1.
As an example, let’s say we start with the number 5.
5 is odd, so we begin by performing (3 * 5) + 1 = 16.
16 is even, so we perform (16/2) = 8.
8 is even, so we perform (8/2) = 4.
4 is even, so we perform (4/2) = 2.
2 is even, so we perform (2/2) = 1.
In this example, our Collatz operation required 5 total iterations to reach 1.
Suggested Pseudocode:

val = mem[VALUE]; num_of_iterations = 0; while (val > 1) { if (val % 2 != 0) {
val = shiftleft(val, 1); val += val; val += 1;
} else { val = shiftright(val, 1);
} num_of_iterations++;
} mem[RESULT] = num_of_iterations;
5 Dot Product
The last assembly program you’ll be writing for this project is a dot product calculator. Given two arrays/vectors in memory, your job is to compute the dot product, and return it back into memory. In mathematics, the dot product is calculated as the sum of multiplication between each pair of vector components. If A = {a1,a2,a3} and B = {b1,b2,b3}, the dot product between A and B would be (a1∗b1)+(a2∗b2)+(a3∗b3). For example,
A = {1, 2, 3}
B = {4, -2, -1}
Dot Product of A and B = (1 * 4) + (2 * -2) + (3 * -1) = -3
In this program, values inside vectors can be positive or negative integers, and you are given 3 input values at labels VECTOR_A, VECTOR_B, and .
1. VECTOR_A represents the starting location of the first vector in memory.
2. VECTOR_B represents the starting location of the second vector in memory.
3. LENGTH represents the length of each individual vector.
6 Debugging
When you turn in your files on Gradescope for the first time, you might not receive a perfect score. Does this mean you change one line and spam Gradescope until you get a 100? No! You can use a handy tool known as tester strings.
1. First off, we can get these tester strings in two places: the local grader or off of Gradescope. To run the local grader:
• Mac/Linux Users:
(a) Navigate to the directory your project is in. In your terminal, not in your browser
(b) Run the command sudo chmod +x grade.sh
(c) Now run ./grade.sh
• Windows Users:
(a) On docker quickstart, navigate to the directory your project is in (b) Run ./grade.sh
When you run the script, you should see an output like this:

Copy the string, starting with the leading ‘B’ and ending with the final backslace. Do not include the quotations.
Side Note: If you do not have docker installed, you can still use the tester strings to debug your assembly code. In your Gradescope error output, you will see a tester string. When copying, make sure you copy from the first letter to the final backslace and again, don’t copy the quotations.

2. Secondly, navigate to the clipboard in your docker image and paste in the string.

3. Next, go to the Test Tab and click Setup Replay String

4. Now, paste your tester string in the box!

5. Now, complx is set up with the test that you failed! The nicest part of complx is the ability to step through each instruction and see how they change register values. To do so, click the step button. To change the number representation of the registers, double click inside the register box.

6. If you are interested in looking how your code changes different portions of memory, click the view tab and indicate ‘New View’

7. Now in your new view, go to the area of memory where your data is stored by CTRL+G and insert the address


7 Deliverables
Note: Please do not wait until the last minute to run/test your project, history has proved that last minute turn-ins will result in long queue times for grading on Gradescope. You have been warned.
8 LC-3 Assembly Programming Requirements
8.1 Overview
1. Your code must assemble with NO WARNINGS OR ERRORS. To assemble your program, open the file with Complx. It will complain if there are any issues. If your code does not assemble you WILL get a zero for that file.
2. Comment your code! This is especially important in assembly, because it’s much harder to interpret what is happening later, and you’ll be glad you left yourself notes on what certain instructions are contributing to the code. Comment things like what registers are being used for and what less intuitive lines of code are actually doing. To comment code in LC-3 assembly just type a semicolon (;), and the rest of that line will be a comment.
3. Avoid stating the obvious in your comments, it doesn’t help in understanding what the code is doing.
Good Comment
ADD R3, R3, -1 ; counter--
BRp LOOP
Bad Comment ; if counter == 0 don’t loop again
ADD R3, R3, -1 ; Decrement R3
BRp LOOP ; Branch to LOOP if positive
4. DO NOT assume that ANYTHING in the LC-3 is already zero. Treat the machine as if your program was loaded into a machine with random values stored in the memory and register file.
5. Following from 3. You can randomize the memory and load your program by doing File - Randomize and Load using complx.
6. Do NOT execute any data as if it were an instruction (meaning you should put .fills after HALT or RET).
7. Do not add any comments beginning with @plugin or change any comments of this kind.
8. Test your assembly. Don’t just assume it works and turn it in.
9 Demos
• Sign up for a demo time slot via Canvas before the beginning of the first demo slot. This is the only way you can ensure you will have a slot.
• Your overall project score will be ((autograder_score * 0.5) + (demo_score * 0.5)), meaning if you received a 90% on your autograder, but a 30% on the demo you would receive an overall score of 60%. If you miss your demo you will not receive any of these points and the maximum you can receive on the project is 50%.
• You will be able to makeup one of your demos at the end of the semester for half credit.
10 Rules and Regulations
10.1 General Rules
2. Please read the assignment in its entirety before asking questions.
4. If you find any problems with the assignment, it would be greatly appreciated if you reported them to the author (which can be found at the top of the assignment). Announcements will be posted if the assignment changes.
10.2 Submission Conventions
2. Do not submit links to files. The autograder does not understand it, and we will not manually grade assignments submitted this way as it is easy to change the files after the submission period ends.
10.3 Submission Guidelines
2. You are also responsible for ensuring that what you turned in is what you meant to turn in. After submitting you should be sure to download your submission into a brand new folder and test if it works. No excuses if you submit the wrong files, what you turn in is what we grade. In addition, your assignment must be turned in via Canvas/Gradescope. Under no circumstances whatsoever we will accept any email submission of an assignment. Note: if you were granted an extension you will still turn in the assignment over Canvas/Gradescope.
4. Projects turned in late receive partial credit within the first 48 hours. We will take off 30% of the points for a project submitted between 0 and 24 hours late, and we will take off 50% of the points for a project submitted between 24 and 48 hours late. We will not accept projects turned in over 48 hours late. This late policy is also in the syllabus.
10.4 Syllabus Excerpt on Academic Misconduct
Academic misconduct is taken very seriously in this class.
3. A student must submit an assignment or project as his/her own work (this is what is expected of the students).
10.5 Is collaboration allowed?
• Publishing your assignments on public repositories accessible to other students is unauthorized collaboration and thus Academic Misconduct.