;; Note that this is scheme syntax wrapping asm for a stack machine
(variable eol 0)
(variable scan 0)
(variable free 0)
;; These need to be initialized with the runtime
(variable eom 0)
(variable old 0) 
(variable new 0)
(variable root 0)

(push main)
(jmp)

alloc ;; ( -- p)
;; Test if free will go beyond eom
(ref free)
(dup) ; ( -- free free)
(push 8)
(+)
(dup) ; ( -- free free+8 free+8)
(ref eom)
(<) ; ( -- free free+8 (free+8 < eom))
(push alloc-do-gc)
(if)
;; write free+8 to free
(set! free)
;; return the old free, it is memory the program can use
(return)
alloc-do-gc
;; Empty the stack
(drop)
(drop)
;; Run garbage collection
(push gc-run)
(call)
;; Tail-call allocation
(push alloc)
(jmp)

gc-run ;; ( -- )
; Move scan & free to start of new memory
(ref new)
(dup)
(set! free)
(set! scan)
(ref root)
(push relocate-cons)
(call)
(push gc-loop)
(call)
; Flip old and new
(ref old)
(dup)
(ref new)
(set! old)
(set! new)
(push 512)
(+)
(set! eom)
(return)

relocate-cons ;; (o -- )
(dup)
(@)
(push relocate-reg)
(call)
(push 4)
(+)
(@)
(push relocate-reg)

relocate-reg ;; (r -- )
(dup)
(push #x80000000) ;; Is this a cons?
(and)
(push reg-relocated)
(if)
(dup)
(ref eol)
(=) ;; Is this eol?
(not)
(push reg-relocated)
(if)
(dup)
(push #x40000000) ;; Is it a broken heart?
(and)
(push copy-and-construct)
(if)
(dup) ;; Broken heart, copy updated address from cdr
(push 4)
(+)
(@)   ;; Retrieve new address
(dup)
(!)   ;; Write it here
(push reg-relocated)
(jmp)
copy-and-construct
(dup) ;; Wasn't a broken heart, move car to new memory
(@) 
(push free)
(!)
(dup) ;; Push cdr to new memory
(push 4)
(+)
(@)
(push free)
(push 4)
(+)
(!)
(push #x40000000)
(over)
(!)
(ref free)
(over)
(push 4)
(+)
(!)
(ref free) ;; Move free pointer
(push 8)
(+)
(set! free)
reg-relocated
(drop)
(return)

gc-loop
(ref free)
(ref scan)
(<)
(branch gc-loop-done)
(ref scan)
(relocate-reg)
(push gc-loop)
(jmp)
gc-loop-done
(return)


main
;; These need to be initialized with the runtime
(push memory)
(dup)
(set! new)
(push 512)
(+)
(dup)
(set! eom)
(set! old)
;; TODO set up root

memory