hanoi1.s

@   VERSIÓN A UTILIZAR POR MORALES CALVO ÁNGEL OMAR
@   Usuario: burgie80

@   hanoi1.s
@   D. Thiebaut
@   Recursive towers of Hanoi
@   See https://en.wikipedia.org/wiki/Tower_of_Hanoi Wikipedia for details.

@ ---------------------------------------
@	Data Section
@ ---------------------------------------
	
	.data
	.balign 4	
string: .asciz  "move disk from %c to %c\n\0"
peg1:	.int	'A'		@ name of Peg 1, must be a char
peg2:	.int	'B'
peg3:	.int	'C'
n:	.int	4		@ number of disks to move

	
@ ---------------------------------------
@	Code Section
@ ---------------------------------------
	
	.text
	.global main
	.extern printf

	
@ ---------------------------------------
@ moveDisks( n, Source, Dest, Extra )
@	    r4   r5     r6    r7
@    if n==1:
@	printf( "move disk from %c to %c\n", Source, Dest )
@    else:
@	moveDisks( n-1, Source, Extra, Desk )
@	printf( "move disk from %c to %c\n", Source, Dest )
@	moveDisks( n-1, Extra, Dest, Source )
@	
moveDisks:	
	push	{r4-r8, lr}

	@ if n==1:
	cmp	r4, #1
	bgt	moveN_1Disks

move1Disk:	
	@ print( "move disk from %c to %c\n", Source, Dest )
	ldr	r0, =string
	mov	r1, r5
	mov	r2, r6
	bl	printf
	b	endMoveDisk

moveN_1Disks:	
	@ moveDisks( n-1, Source, Extra, Dest )
	mov	r8, r7		@ swap Dest & Extra
	mov	r7, r6
	mov	r6, r8
	sub	r4, #1
	bl	moveDisks
	mov	r8, r7		@ unswap Dest & Extra
	mov	r7, r6
	mov	r6, r8

	@ print( "move disk from %c to %c\n", Source, Dest )
	ldr	r0, =string
	mov	r1, r5
	mov	r2, r6
	bl	printf

	@ moveDisks( n-1, Extra, Dest, Source )	
	mov	r8, r5		@ swap Source and Extra, i.e. r5 and r7.
	mov	r5, r7
	mov	r7, r8
	bl	moveDisks
	
endMoveDisk:	
	pop	{r4-r8, pc}

	
@ ---------------------------------------
@ main: call moveDisks( n, peg1, peg2, peg3 )

main:   push 	{ip, lr}	@ push return address + dummy register
				@ for alignment

	ldr	r4, =n		@ pass n
	ldr	r4, [r4]
	ldr	r5, =peg1	@ pass peg1
	ldr	r5, [r5]
	ldr	r6, =peg2	@ pass peg2
	ldr	r6, [r6]
	ldr	r7, =peg3	@ pass peg3
	ldr	r7, [r7]
	bl	moveDisks	@ call moveDisks( n, peg1, peg2, peg3 )

	
@ return to OS	
        pop 	{ip, pc}	@ pop return address into pc