MIPS-使用循环故障将值存储到数组中

Question

I am relatively new to MIPS and have been finding example problems to expand my skills. I am faced with this problem:

Subtract elements of one arrary from another and replace values in the first array.

Given arrays a and b, each 10 words long, for each value i where 0 <= i < 10, let c = A[i] - B[i]. Then, if c < 0 set A[i] = 0. Otherwise, set A[i] = c.

Complete the code so that the data values are correctly loaded, computed and stored. You must use a loop to iterate through the loads and stores

Here is my coded attempt, however I notice my $12 and $13 are not loading in the first value of a and b respectively as I would like them to. Any help would be very greatly appreciated!

.data 0x10010000
.word 23     # a[0]
.word 6
.word 11
.word 7
.word 44
.word 32
.word 9
.word 16
.word 29
.word 13

.data 0x10010040
.word 6  # b[0]
.word 22
.word 9
.word 1
.word 3
.word 15
.word 10
.word 4
.word 30
.word 8


.text
.globl main



main:

lui $16, 0x1001  # $16 contains the address of a[0]

add $17, $16, 0
ori $17, $17, 0x0040     # $17 contains the address of b[0]
li $9, 0                #initiate iterator value
loop: 
lw $12, 0($16)      #load register with value of a
nop
lw $13, 0($17)      #load register with value of b
nop

li $8, 0                #set c to 0
sub $8, $12, $13        # c = A(i) - B(i)
blt $8, 0, negative     # if c is negative branch
nop
li $12, 0
add $12, $12, $8        #else A(i) = c
addi $9, $9, 1          #add 1 to iteration value
sw $12, 0($16)          #store value back into a
nop
bne $9, 10, update      #check that we have not the last array
nop
b exit                  #if so finish program
nop
negative:
li $12, 0
sw $12, 0($16)          #store value back into a
addi $9, $9, 1          #add 1 to iteration value
beq $9, 10, exit
nop
b loop
nop
update:
add $16, $16, 4         #move to the next value in a
add $17, $17, 4         #move to next value in b
b loop
nop
exit:
b exit
nop

Answer 1

You are not updating your pointers ( $16 and $17 ) when the result of the subtraction is negative. You should remove the lines

  nop
  b loop
  nop

located after the beq $9, 10, exit after the negative label.

Something else I noticed in your code is that you put a nop after every lw and sw , which is not needed.