GC cartable 地址映射算法

 

inline void* CardTable::AddrFromCard(const uint8_t *card_addr) const {
  DCHECK(IsValidCard(card_addr))
    << " card_addr: " << reinterpret_cast<const void*>(card_addr)
    << " begin: " << reinterpret_cast<void*>(mem_map_->Begin() + offset_)
    << " end: " << reinterpret_cast<void*>(mem_map_->End());
  uintptr_t offset = card_addr - biased_begin_;
  return reinterpret_cast<void*>(offset << kCardShift);
}

inline uint8_t* CardTable::CardFromAddr(const void *addr) const {
  uint8_t *card_addr = biased_begin_ + (reinterpret_cast<uintptr_t>(addr) >> kCardShift);
  // Sanity check the caller was asking for address covered by the card table
  DCHECK(IsValidCard(card_addr)) << "addr: " << addr
      << " card_addr: " << reinterpret_cast<void*>(card_addr);
  return card_addr;
}

效率提高40%