@ hanoi.s
@ D. Thiebaut
@ Recursive towers of Hanoi, version with FIXED DISK
@ 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
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, Dest )
@ 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
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
