arm assembly collatz conjecture

/*
 * collatz.s
 * Computes the collatz conjecture of n
 */
	.syntax unified
	.global _start

_start:
	mov r0, 0 
	mov r1, 6 @n = 6
loop:
	cmp r1, 1		
	ble _exit
	and r2, r1, 1 		
	cmp r2, 1		
	beq odd
	bne even
even:
	mov r1, r1, ASR 1 @ r1/2
	add r0, r0, 1
	bal loop
odd:
	mov r3, 3
	mul r1, r3 @ r1 * 3
	add r1, r1, 1 @ r1 + 1
	add r0, r0, 1	
	bal loop
_exit:
	mov r7, 1
	swi 0