factor/vm/write_barrier.hpp

/* 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);
static const cell deck_size = (1 << deck_bits);
static const cell addr_deck_mask = (deck_size - 1);

inline cell addr_to_card(cell a) { return a >> card_bits; }

inline cell addr_to_deck(cell a) { return a >> deck_bits; }
}