sum:
	addi $a0,$zero,$zero # $s0=0
	addi $t2, $zero,$zero # $t2=0
loop:
	lbu $t0, 0($a0)
	beq $t0,$zero, case1
	addi $t1,$zero,32
	beq $t0, $t1, case2
	addi $t2,$t2,1
	addi $a0,$a0,1
	j loop
case1:
	addi $v0,$t2,0
	jr $ra
case2:
	addi $a0,$a0,4
	addi $t2,$zero,0
	j loop