Iterative Binary Search in MIPS - mips

Question

I'm trying to create a iterative binary search in mips, below is my code. It works when searching for the middle value, otherwise it doesnt but i'm not sure why. I'm new to MIPs and trying to get better so any critique is appreciated
.data
myArray: .word 1 4 5 7 9 12 15 17 18 20 21 30
last: #the address that comes after the array
arraySize: .word 11
.globl main
.text
main:
la $s0, myArray # array address
lw $s1, arraySize # arraysize
li $s2, 30 # address of last array entry
jal Binsearch # perform binary search
li $v0, 10
syscall
Binsearch:
li $t0,0 #first = 0
subu $t1, $s1, 1 #last = array size -1
Loop: bge $t0, $t1, DONE # if ! (first < last)
add $t2,$t0,$t1 #first + last
li $t3,2
div $t2, $t3 #$LO = middle index
mflo $t3 #$t3 = middle index
li $s3,4 #load the value 4 into s3
multu $s3, $t3 #multiply middle by 4 to get the offset
mflo $t4 #store the result in t4
add $t4, $s0, $t4 #t4 points to array[mid]
lw $t5, ($t4) #load the value at array[mid] into t5
beq $t5, $s2, return_mid # if t5 == s2 then return the index
blt $t5, $s2, move_right # if t5 < s2 then move right
subu $t1, $t3, 1 #if this line is reached that means that none of the above
j Loop #conditions are true, so t5 > s2, last = mid -1
return_mid:
li $v0, 1
add $a0, $t3, $zero # add the middle index to a0
syscall #print the index
move_right:
addi $t0, $t3, 1 # first = mid + 1
j Loop # jump to Loop
DONE:
li $v0, 1
li $a0, -1
syscall
j $ra #return to the caller

Answer 1

I figured it out, had to test for some corner cases and change the LOOP condition
.data
myArray: .word 1 4 5 7 9 12 15 17 18 20 21 30
last: #the address that comes after the array
arraySize: .word 11
.globl main
.text
main:
la $s0, myArray # array address
lw $s1, arraySize # arraysize
li $s2, 20 #value youre searching for
jal Binsearch # perform binary search
li $v0, 10
syscall
Binsearch:
li $t0,0 #first = 0
move $t1, $s1 #last = array size -1
li $t6,1
li $t7,4 #checks for the last element in the array being the correct value
multu $t7,$t1
mflo $t7
add $t7,$s0,$t7
lw $t5, ($t7)
beq $t5, $s2, last_num # if == then
subu $t1, $s1, 1
Loop: bge $t0, $t1, DONE # if ! (first < last)
add $t2,$t0,$t1 #first + last
li $t3,2
div $t2, $t3 #$LO = middle index
mflo $t3 #$t3 = middle index
beq $t2,$t6, special_case #if first+last = 1 you want totake HI not LO
li $t7,4 #load the value 4 into t7
multu $t7, $t3 #multiply middle by 4 to get the offset
mflo $t4 #store the result in t4
add $t4, $s0, $t4 #t4 points to array[mid]
lw $t5, ($t4) #load the value at array[mid] into t5
beq $t5, $s2, return_mid # if t5 == s2 then return the index
blt $t5, $s2, move_right # if t5 < s2 then move right
subu $t1, $t3, 1 #if this line is reached that means that none of the above
j Loop #conditions are true, so t5 > s2, last = mid -1
special_case:
mfhi $t3 #get the 1 value from hi
li $t7,4 #load the value 4 into t7
multu $t7, $t3 #multiply middle by 4 to get the offset
mflo $t4 #store the result in t4
add $t4, $s0, $t4 #t4 points to array[mid]
lw $t5, ($t4) #load the value at array[mid] into t5
beq $t5, $s2, return_mid # if t5 == s2 then return the index
return_mid:
li $v0, 1
add $a0, $t3, $zero # add the middle index to a0
syscall #print the index
j $ra
move_right:
addi $t0, $t3, 1 # first = mid + 1
j Loop # jump to Loop
last_num:
li $v0, 1
add $a0, $t1, $zero
syscall
j $ra
DONE:
li $v0, 1
li $a0, -1
syscall
j $ra #return to the caller