Infinite array loop MIPS

Question

So I'm new to MIPS and I'm trying to build a program in Assembly MIPS which finds the maximum value in array:

    .data 
    A: .word 11 100 3 5 8 13 1 16  #array of integers
    N: .word 8  # array length
    output_max: .asciiz "The max value is: "
    
    .text
    .globl main
    
main:
    la $a0 N
    la $a1 A
    
    jal max
    move $s0 $v0
    
    
    li $v0 4
    la $a0 output_max
    syscall
    
    li $v0 1
    move $a0 $s0
    syscall
    j exit
    
    
exit:
    li $v0 10
    syscall

max:
    
    move $t0 $a0  
    move $t1 $a1  
    lw $v0 0($t1)  
    li $t2 0  
    j maxLoop
    
maxLoop:
    addi $t2 $t2 1 
    beq $t2 $t0 maxEnd  
    addi $t1 $t1 4 
    lw $t3 0($t1)
    slt $t4 $v0 $t3 
    beq $t4 1 changeMax
    j maxLoop
    
changeMax:
    move $v0 $t3
    j maxLoop
        

maxEnd:
    jr $ra

The max function should return the maximum value in the input array. So after compiling, it goes into an infinite loop. I can't quite see where the problem is..

Did you try debugging it?

Erik Eidt
– Erik Eidt

2021-06-02 19:06:07 +00:00
Commented Jun 2, 2021 at 19:06 — Erik Eidt
– Erik Eidt, Commented Jun 2, 2021 at 19:06

Unn · Accepted Answer · 2021-06-02 16:49:06Z

1

The problem is you are running your loop using the address of N and not the value of N. The first line of main loads the address of N into $a0 which becomes $t0 in your max function. However, you then use that address as if its the value of N (ie, 8) in your loop with beq $t2 $t0 maxEnd.

Either just load the value directly into $a0 at the beginning:

main:
    li $a0 8 # Length of A

Or dereference the argument in max first:

max:
    lw $t0 0($a0) # Get value of N from pointer to N

answered Jun 2, 2021 at 16:49

Unn

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