pointers

ptr_stack.c

void _pstack_init(void *stack) {
 *(void **)stack = (char *)stack + sizeof (char *);
}

void   _pstack_push(void *stack, void *data) {
  *(void **)stack = (char *)*(void **)stack + sizeof (char *);
  **(void ***)stack = data;
}

void   _pstack_pop (void *stack)             {
  **(void ***)stack = 0;
  *(void **)stack = (char *)*(void **)stack - sizeof (char *);
}

void * _pstack_peek(void *stack)             {
  return **(void ***)stack;
}


const int list_size = 1 << 8; /* 256 */

void _pq_init(void *list) {
  ((long **)list)[0] = 0; /* tail */
  ((long **)list)[1] = 0; /* head */
}

long _pq_length(void *list) {
  long tail = ((long *)list)[0];
  long head = ((long *)list)[1];
  return (list_size - tail) - (list_size - head);
}

void _pq_shift(void *list, void *data) {
  long head = ((long *)list)[1];
  char **ptr;
  ptr = (char **) list + (2 * sizeof(long *)) + (head * sizeof(void *));
  *ptr = data;
  head = head + 1;
  head = head & (list_size - 1);
  ((long *)list)[1] = head;
}

void * _pq_pop(void *list) {
  long tail = ((long *)list)[0];
  char **ptr;
  ptr = (char **) list + (2 * sizeof(long *)) + (tail * sizeof(void *));
  tail = tail + 1;
  tail = tail & (list_size - 1);
  ((long *)list)[0] = tail;
  return *ptr;
}