/* If a runtime function needs to call another function which potentially
allocates memory, it must store any local variable references to Factor
objects on the root stack */

/* GC locals: stores addresses of pointers to objects. The GC updates these
pointers, so you can do

REGISTER_ROOT(some_local);

... allocate memory ...

foo(some_local);

...

UNREGISTER_ROOT(some_local); */
F_SEGMENT *gc_locals_region;
CELL gc_locals;

DEFPUSHPOP(gc_local_,gc_locals)

#define REGISTER_ROOT(obj) gc_local_push((CELL)&obj)
#define UNREGISTER_ROOT(obj) \
	{ \
		if(gc_local_pop() != (CELL)&obj) \
			critical_error("Mismatched REGISTER_ROOT/UNREGISTER_ROOT",0); \
	}

/* Extra roots: stores pointers to objects in the heap. Requires extra work
(you have to unregister before accessing the object) but more flexible. */
F_SEGMENT *extra_roots_region;
CELL extra_roots;

DEFPUSHPOP(root_,extra_roots)

#define REGISTER_UNTAGGED(obj) root_push(obj ? tag_object(obj) : 0)
#define UNREGISTER_UNTAGGED(obj) obj = untag_object(root_pop())

/* We ignore strings which point outside the data heap, but we might be given
a char* which points inside the data heap, in which case it is a root, for
example if we call unbox_char_string() the result is placed in a byte array */
INLINE bool root_push_alien(const void *ptr)
{
	if(in_data_heap_p((CELL)ptr))
	{
		F_BYTE_ARRAY *objptr = ((F_BYTE_ARRAY *)ptr) - 1;
		if(objptr->header == tag_header(BYTE_ARRAY_TYPE))
		{
			root_push(tag_object(objptr));
			return true;
		}
	}

	return false;
}

#define REGISTER_C_STRING(obj) \
	bool obj##_root = root_push_alien(obj)
#define UNREGISTER_C_STRING(obj) \
	if(obj##_root) obj = alien_offset(root_pop())

#define REGISTER_BIGNUM(obj) if(obj) root_push(tag_bignum(obj))
#define UNREGISTER_BIGNUM(obj) if(obj) obj = (untag_object(root_pop()))