factor/vm/free_list.hpp

namespace factor {

static const cell free_list_count = 32;
static const cell allocation_page_size = 1024;

struct free_heap_block {
  cell header;

  bool free_p() const { return (header & 1) == 1; }

  cell size() const {
    cell size = header & ~7;
    FACTOR_ASSERT(size > 0);
    return size;
  }

  void make_free(cell size) {
    FACTOR_ASSERT(size > 0);
    header = size | 1;
  }
};

struct block_size_compare {
  bool operator()(free_heap_block* a, free_heap_block* b) const {
    return a->size() < b->size();
  }
};

typedef std::multiset<free_heap_block*, block_size_compare> large_block_set;

struct free_list {
  std::vector<free_heap_block*> small_blocks[free_list_count];
  large_block_set large_blocks;
  cell free_block_count;
  cell free_space;

  void clear_free_list();
  void initial_free_list(cell start, cell end, cell occupied);
  void add_to_free_list(free_heap_block* block);
  free_heap_block* find_free_block(cell size);
  free_heap_block* split_free_block(free_heap_block* block, cell size);
  bool can_allot_p(cell size);
  cell largest_free_block();
};

}