strlen:
li $t0, 0 #initialize the count to zero
loop:
  lbu $t1, 0($a0) # load the next character into t1
  beqz $t1, exit # check for the null character
  addi $a0, $a0, 1 # increment the string pointer
  addi $t0, $t0, 1 # increment the count
  j loop # return to the top of the loop
exit: