ROT p1 2017

rg.s

main:
  # n = 6
	addi $s0, $zero, 6
	
  # por padrao registradores $aX guardam os params
  add  $a0, $s0, $zero

  # chama rotina
	jal  ROT

  # result = rot(n)
	add  $s1, $zero, $v0 

ROT:
	addi $t0, $zero, 2
	slt  $t1, $a0, $t0
  # a < 2
	bne  $t1, $zero, LT2
  # a = 2
	beq  $t0, $a0, EQ2
	
  # empilhamento de argumento e end. de retorno
	addi $sp, $sp, -8
	sw   $a0, 0($sp)
	sw   $ra, 4($sp)

  # a = a - 2
	sub  $a0, $a0, $t0
  # chamada recursiva
	jal  ROT
  
  # return 1 + $v0 da recursao
	addi $v0, $v0, 1


  # desempilha
	lw   $a0, 0($sp)
	lw   $ra, 4($sp)
	addi $sp, $sp, 8

  # retorna
	jr $ra

LT2:
	and  $v0, $zero, $zero
	jr $ra

EQ2:
	addi $v0, $zero, 1
	jr $ra