text: /* card marking write barrier. a card is a byte storing a mark flag,
  and the offset (in cells) of the first object in the card.
  
  the mark flag is set by the write barrier when an object in the
  card has a slot written to.
  
  the offset of the first object is set by the allocator. */
  
  namespace factor {
  
  /* if card_points_to_nursery is set, card_points_to_aging must also be set. */
  static const cell card_points_to_nursery = 0x80;
  static const cell card_points_to_aging = 0x40;
  static const cell card_mark_mask =
      (card_points_to_nursery | card_points_to_aging);
  typedef uint8_t card;
  
  static const cell card_bits = 8;
  static const cell card_size = 1 << card_bits;
  static const cell addr_card_mask = card_size - 1;
  
  typedef uint8_t card_deck;
  
  static const cell deck_bits = card_bits + 10;
  /* Number of bytes on the heap a deck addresses. Each deck as 1024
     cards. So 256 kb. */
  static const cell deck_size = 1 << deck_bits;
  static const cell cards_per_deck = 1 << 10;
  
  inline cell addr_to_card(cell a) { return a >> card_bits; }
  
  inline cell addr_to_deck(cell a) { return a >> deck_bits; }
  }
  