gistfile1.h

static inline int
is_pointer_to_heap(ptr)
    void *ptr;
{
    RVALUE *p = RANY(ptr);
    struct heaps_slot *heap;

    if (p < lomem || p > himem || (VALUE)p % sizeof(RVALUE)) return Qfalse;

    /* check if p looks like a pointer */
    heap = heaps+heaps_used;
    while (--heap >= heaps) 
      if (p >= heap->slot && p < heap->slot + heap->limit)
        return Qtrue;
    return Qfalse;
}