073 treedepth.s

.data
A: .word B, C
B: .word 0, 0
C: .word 0, 0

.text
.global _start

_start:
    ldr r0, =A
    mov r1, #2
    bl depth
    1: b 1b

.global depth
depth:
	push {lr}
	bl deep
    cmp r0, r1
    mov r0, #0
    movls r0, #1 
    
    pop {lr}
    bx lr

deep:
	push {r1-r3, lr}
    mov r1, r0
    
    ldr r2, [r1, #0]
    cmp r2, #0
    beq skip1
    
    mov r0, r2
    bl deep
    mov r2, r0
skip1:
    ldr r3, [r1, #4]
    cmp r3, #0
    beq skip2
    
    mov r0, r3
    bl deep
    mov r3, r0
skip2:
	cmp r2, r3
    movhs r0, r2
    movlo r0, r3  

    add r0, #1    
  	pop {r1-r3, lr}
    bx lr