es.s

.globl main

.data
W: .asciiz "+6-4+3-2"

.text
main:
	la $a0, W # a0 = W_address
	
	jal calc
	
	move $a0, $v0 # a0 = v0
	li $v0, 1 # print int
	syscall
	li $v0, 10 # exit
	syscall

calc:
	# push stack
	subi $sp, $sp, 12
	sw $a0, 8($sp)
	sw $fp, 4($sp)
	sw $ra, 0($sp)
	
	# index
	
	# helpers
	move $t2, $zero # t2 = 0, used to store the value of the current number
	
	# result
	move $v0, $zero # v0 = 0
	
	# conditions
	addi $s0, $s0, '-'
	addi $s1, $s1, '+'
	addi $s2, $s2, 1
	
	loopString:
		lb $t1, 0($a0) # t1 = mem[a0], the current character
		beq $t1, $zero, exitLoopString # exit if the current character is the null char \0
		
		beq $t1, $s1, dontSetFlag
		beq $t1, $s0, setFlag 
		
		subi $t2, $t1, 0x30 # t2 = t1 - 0x30, because 0x3 is the ascii value for '0'
		
		beq $t3, $s2, invertIndex # if the flag is set, invert the index
		beq $t3, $zero, updateTotal # if the flag is not set, just update the total
		
		invertIndex:
			sub $t2, $zero, $t2 # t2 = 0 - t2, invert the current value
			j updateTotal
			
		updateTotal:
			add $v0, $v0, $t2 # v0 += t2, update the current total
			j loopEnd
		
		loopEnd:
			add $a0, $a0, 1 # a0 += 1
			j loopString
	exitLoopString:
	
	# pop stack
	lw $ra, 0($sp)
	lw $fp, 4($sp)
	lw $a0, 8($sp)
	addi $sp, $sp, 12
	
	jr $ra

dontSetFlag:
	move $t3, $zero
	j loopEnd
setFlag:
	move $t3, $zero
	addi $t3, $t3, 1
	j loopEnd