COMP2421 Assignment 2

MA Mingyu (Derek) | 14110562D | Oct 2, 2017
derek.ma | derek.ma@connect.polyu.hk

Question 1

    # Get value of A[20]
    lw $t3, 80($s2)       # load word at address $t2 to $t3

    # Get value of B[A[20]]
    mul $t4, $t3, 4     # get index
    add $t5, $s3, $t4   # calculate offset
    lw $t6, ($t5)       # load word at that address

    # Add y to value of B[A[20]]
    add $s0, $s1, $t6

Full executable program for verification is attached below.

Question 2

loop: 
    # Check condition for this while loop
    slti $t8, $s0, 10   # t8 is 1 if the condition satisfies, 0 if not
    beq $t8, $zero, exit # if condition doesn't hold ,exit without getting into the loop

    add $t0, $s0, $s1   # add x and y and save to $t0

    mul $t3, $s0, 4     # $t3 is the offset
    add $t4, $s2, $t3   # $t4 is the address of A[20]
    sw $t0, ($t4)       # store the value to address
    
    addi $t1, $s0, 1    # add 1 to x value
    move $s0, $t1

    j loop              # run the loop body again

exit:    
    # program to be run after the while loop

Full executable program for verification is attached below.

Question 3

// Assume variable x and y are already been declaimed with values
    int i;
    i = 0;
    while (y != 0){
        i += x;
        y -= 1;
    }
    i += 1;
    return i;

This function calculate the value of \(x \times y+1\) and return the value.

Question 4

    # Check condition in if statement
    slt $t5, $t1, $t2       # compare values in $t1 and $t2
    beq $t5, $zero, L1      # if $t5 is zero, x<y not satisfied, exit
    bne $t3, $zero, L1      # if condition doesn't hold ,exit without getting into the loop

    li $t4, 1               # set value of w to 1
    
    j L1
L1:
    # program after this instruction

Full programs for verification

Program for question 1

# assign2_1.s

    .data
arrayA:   .word  0:20       # assume array A has length of 20
arrayB:   .word  0:20       # assume array A has length of 20

    .globl main # Global variable: the entry point of the prog.

    .text
main:
    # Pre-process: load all values to registers
    li $s1, 5 # assume y is 5
    la $s2, arrayA # load base address of array A
    la $s3, arrayB # load base address of array B

    # Get value of A[20]
    lw $t3, 80($s2)       # load word at address $t2 to $t3

    # Print value of A[20]
    move $a0, $t3
    li $v0, 1
    syscall

    # Get value of B[A[20]]
    mul $t4, $t3, 4     # get index
    add $t5, $s3, $t4   # calculate offset
    lw $t6, ($t5)       # load word at that address

    # Print value of B[A[20]]
    move $a0, $t6
    li $v0, 1
    syscall

    # Add y to value of B[A[20]]
    add $s0, $s1, $t6

    # Print final value for x
    move $a0, $s0
    li $v0, 1
    syscall

    # Terminate the program
    li $v0, 10
    syscall

Program for question 2

Following verification programs do not simulate function call part, just logical operations part.

# assign2_2.s

    .data
array:   .word  0:10    # assume array A has length of 20

    .globl main

    .text
main:
    # Pre-process: load all values to registers
    li $s0, 1           # assume x is 1
    li $s1, 5           # assume y is 5
    la $s2, array       # load base address of array

loop: 
    # Check condition for this while loop
    slti $t8, $s0, 10   # t8 is 1 if the condition satisfies, 0 if not
    beq $t8, $zero, exit # if condition doesn't hold ,exit without getting into the loop

    add $t0, $s0, $s1   # add x and y and save to $t0

    mul $t3, $s0, 4     # $t4 is the offset
    add $t4, $s2, $t3   # $t5 is the address of A[20]
    sw $t0, ($t4)       # store the value to address
    
    addi $t1, $s0, 1    # add 1 to x value
    move $s0, $t1

    # Print out the result for verification
    move $a0, $t0
    li $v0, 1
    syscall

    move $a0, $s0
    li $v0, 1
    syscall

    j loop              # run the loop body again

exit:    
    # Terminate the program
    li $v0, 10
    syscall

Programs for question 3

Following verification programs do not simulate function call part, just logical operations part.

# assign2_3.s

    .data
str1: .asciiz "------\n"

    .globl main # Global variable: the entry point of the prog.

    .text
main:
    li $a3, 3
    li $a1, 17
    add $t0, $zero, $zero
loop: 
    beq $a1, $zero, Done

    move $a0, $t0
    li $v0, 1
    syscall

    move $a0, $a3
    li $v0, 1
    syscall

    add $t0, $t0, $a3

    move $a0, $t0
    li $v0, 1
    syscall

    sub $a1, $a1, 1

    move $a0, $a1
    li $v0, 1
    syscall

    j loop

Done: 
    la $a0, str1 # load string address into $a0 and I/O code into $v0 
    li $v0, 4
    syscall
    addi $t0, $t0, 1

    move $a0, $t0
    li $v0, 1
    syscall

    #add $v0, $t0, $zero
    li $v0, 10
    syscall
// assign2_3.c

#include <stdio.h>
int main () {
    int x, y;
    x = 3;
    y = 17;
    // Assume variable x and y are already been declaimed with values
    int i;
    i = 0;
    while (y != 0){
        i += x;
        y -= 1;
    }
    i += 1;
    // return i;
    printf("%d", i);
}

Program for question 4

# assign2_4.s

    .data
str1: .asciiz "Getting in the if body\n"

    .globl main # Global variable: the entry point of the prog.

    .text
main:

    li $t1, 3 # x
    li $t2, 4 # y
    li $t3, 0 # z
    li $t4, 0

    slt $t5, $t1, $t2 # compare values in $t1 and $t2
    beq $t5, $zero, L1 # if $t5 is zero, x<y not satisfied, exit
    bne $t3, $zero, L1 # if condition doesn't hold ,exit without getting into the loop
    
    la $a0, str1
    li $v0, 4
    syscall

    li $t4, 1 # set value of w to 1
    j L1
L1:
    move $a0, $t4
    li $v0, 1
    syscall

    li $v0, 10
    syscall

References

http://pages.cs.wisc.edu/~smoler/cs354/onyourown/arrays.html

http://logos.cs.uic.edu/366/notes/mips%20quick%20tutorial.htm

https://www.cs.umd.edu/class/sum2003/cmsc311/Notes/Mips/cond.html

https://www.cs.umd.edu/class/sum2003/cmsc311/Notes/Mips/pseudojump.html