set a, data
jsr strlen
set b, a
set a, data
jsr reverse
jsr print
set PC, end

; reverse the string in place at [a], of len b
:reverse
  set PUSH, a
  sub b, 1; len - 1
  set i, 0; start
  set a, POP
:doreverse
  ifg i, b
    set PC, POP

  set x, a
  add x, i

  set y, a
  add y, b

  set c, [x]
  set [x], [y]
  set [y], c

  add i, 1
  sub b, 1

  set PC, doreverse


:strlen
    set i, 0
:docount
    ife [a], 0x0
        set PC, countend
    add i, 1
    add a, 1
    set PC, docount
:countend
    set a, i
    set PC, POP


; print the string at [a] ending with 0x0
:print
    set PUSH, a
    set i, 0
:doprint
    ife [a], 0x0
        set PC, printend
    set [0x8000+i], [a]
    add i, 1
    add a, 1
    set PC, doprint
:printend
    set a, POP
    set PC, POP


:end
  set PC, end

:data
  dat "Hello world"

:itoa
    set j, 0 ;index
    set z, 48

    set i, a
    mod i, 10
    div a, 10
    add z, i
    set [0x1000+j], z
    add j, 1
    set z, 48

    ifg a, 0
        sub PC, 11

    set [0x1000+j], 0x0
    set PC, POP