.text
	.align 2
	.globl _sum
	; r3 = len
	; r4 = addr of arr
_sum:
	mr. r0,r3     ; move register: r0 := r3; where '.' enables
				  ; a CR0 update
	blelr- 0      ; branch to LR if "less than or equal" in CR0
				  ; is set, where '-' predicts the branch will
				  ; not be taken
	mtctr r0      ; move r0 into CTR
	li r3,0       ; load immediate: r3 := 0
	addi r4,r4,-4 ; add immediate: r4 := r4 + (-4)
.loop:
	lwzu r0,4(r4) ; load word with update: r0 := mem[r4 + 4];
				  ;                        r4 := r4 + 4
	add r3,r3,r0  ; add to sum: r3 := r3 + r0
	bdnz .loop    ; decrement CTR and branch to loop if not zero
	blr           ; branch to LR