Building a Multiplication Routine in MARIE Assembly: A Step-by-Step Guide

Introduction to MARIE Assembly and Multiplication

In the CDA3103 Project 1, you are tasked with writing a MARIE assembly program that computes z = a * b * c. Since MARIE does not have a multiply instruction, you must implement multiplication using repeated addition. This guide will walk you through the algorithm, code structure, and testing on the MARIE simulator. All numbers are positive integers.

Understanding the Multiplication Algorithm

Multiplication can be performed by repeated addition. For example, 4 * 3 is 4 + 4 + 4 = 12. To compute a * b, add a to itself b times. Then multiply the result by c similarly.

Step-by-Step Algorithm

1. Read input a and display it.
2. Read input b and display it.
3. Read input c and display it.
4. Compute temp = a * b using a loop that adds a repeatedly b times.
5. Compute z = temp * c using a similar loop.
6. Display the result z.

MARIE Assembly Code Structure

Below is a template for the program. Replace Your Name with your actual name.

        ORG 100
        / Program to compute z = a * b * c
        / Your Name
        / Input a, b, c; display each; output z
        INPUT
        STORE a
        OUTPUT
        INPUT
        STORE b
        OUTPUT
        INPUT
        STORE c
        OUTPUT
        / Multiply a * b -> temp
        LOAD a
        STORE temp
        LOAD b
        STORE count
Loop1,  SUBT one
        SKIPCOND 000
        JUMP EndMul1
        LOAD temp
        ADD a
        STORE temp
        LOAD count
        JUMP Loop1
EndMul1, / temp = a * b
        / Multiply temp * c -> z
        LOAD temp
        STORE z
        LOAD c
        STORE count
Loop2,  SUBT one
        SKIPCOND 000
        JUMP EndMul2
        LOAD z
        ADD temp
        STORE z
        LOAD count
        JUMP Loop2
EndMul2, / Output result
        LOAD z
        OUTPUT
        HALT
a,      DEC 0
b,      DEC 0
c,      DEC 0
temp,   DEC 0
z,      DEC 0
count,  DEC 0
one,    DEC 1

Explanation of the Code

The program uses three main sections: input, first multiplication loop, and second multiplication loop. Variables a, b, c store inputs. temp holds the intermediate product. count is a loop counter initialized to the multiplier. The one constant is used to decrement the counter.

In each multiplication loop, we subtract 1 from count and check if it becomes zero using SKIPCOND 000 (skip if AC = 0). If not zero, we add the multiplicand to the running product and repeat.

Testing on the MARIE Simulator

After writing the code in a .mas file, load it into the MARIE simulator. Assemble the code, then run step-by-step or continuously. Enter positive integers for a, b, and c. Verify that each input is displayed and the final result is correct. For example, with a=2, b=3, c=4, you should see output 2, 3, 4, 24.

Common Pitfalls and Tips

• Ensure all variables are initialized to 0 before use.
• The SKIPCOND instruction checks the AC value. After subtracting 1, if AC becomes 0, the next instruction is skipped.
• Use ORG 100 to start the program at address 100 (typical for MARIE).
• Include comments for clarity, especially for your name as required.

Trend Connection: Multiplication in AI and Gaming

Multiplication is fundamental in computer graphics, AI calculations, and even in popular games like Minecraft where coordinates are multiplied for world generation. Understanding low-level multiplication in MARIE helps you appreciate how modern CPUs handle arithmetic efficiently.

Conclusion

By following this guide, you can successfully implement multiplication in MARIE assembly for CDA3103 Project 1. Test thoroughly and ensure your .mas file includes your name as a comment. Good luck!