MIPS, function call goes to infinite loop

Question

C code

int GCD(int m, int n) 
{ //Call MACRO PRINTARGS as the first line of code in GCD 
 //PRINTARGS($a0, $a1) 

 int result = 0; 

 // Base Case: 
if(m == n) 
 result = m; 
else if (m > n) 
// Recursive Case: 
 result = GCD(m-n, n); 
else 
// Recursive Case: 
 result = GCD(m, n-m); 

 //Call MACRO PRINTARGS as the last line of code in GCD before jr $ra 
//PRINTARGS($a0, $a1) 
return result; 
}

GCD: my function will go infinite loop if the first argument is large than second argument (Except the case m=2, n=1)

$a2 is m
$a3 is n
$v1 is where i store the result 

The Greatest Common Denominator (GCD) is the largest positive integer that divides the two numbers without a remainder. (PRINTARGS is just a function i wrote to print the value of m and n every time it runs the loop)

GCD:
PRINTARGS($a2,$a3)
addi $sp $sp,-4
sw $ra 0($sp)

lb $a0,newline
li $v0,11
syscall     #print new line
li $v1,0    # result = 0 result = v1
#base case
bne $a2,$a3,else2   #if m!=n, go to else2
move $v1,$a2        #move value m to v1
j GCD_DONE          #jump to GCD_DONE
#Recursive Case: else if (m > n), result = GCD(m-n, n); 
else2:
blt $a2,$a3,else3   #if m >n jump to else 3
sub $a2,$a2,$a3 #m-n
jal GCD
else3:
#Recursive Case: result = GCD(m, n-m); 
sub $a3,$a3,$a2 #n-m
jal GCD
PRINTARGS($a2,$a3)
GCD_DONE:
addi $sp $sp,4
lw $ra 0($sp)
jr $ra

Answer 1

Two things:

Firstly, in the else2 clause, the function continues execution into else3 after the recursive call. Change to this:

else2:
    blt $a2,$a3,else3   #if m >n jump to else 3
    sub $a2,$a2,$a3 #m-n
    jal GCD
    j GCD_DONE

Also, you should be incrementing $sp after restoring from the stack.