OpenJDK GC patch, original code

cardTableRS.cpp

void ClearNoncleanCardWrapper::do_MemRegion(MemRegion mr) {
  assert(mr.word_size() > 0, "Error");
  assert(_ct->is_aligned(mr.start()), "mr.start() should be card aligned");
  // mr.end() may not necessarily be card aligned.
  jbyte* cur_entry = _ct->byte_for(mr.last());
  const jbyte* limit = _ct->byte_for(mr.start());
  HeapWord* end_of_non_clean = mr.end();
  HeapWord* start_of_non_clean = end_of_non_clean;
  while (cur_entry >= limit) {
    HeapWord* cur_hw = _ct->addr_for(cur_entry);
    if ((*cur_entry != CardTableRS::clean_card_val()) && clear_card(cur_entry)) {
      // Continue the dirty range by opening the
      // dirty window one card to the left.
      start_of_non_clean = cur_hw;
    } else {
      // We hit a "clean" card; process any non-empty
      // "dirty" range accumulated so far.
      if (start_of_non_clean < end_of_non_clean) {
        const MemRegion mrd(start_of_non_clean, end_of_non_clean);
        _dirty_card_closure->do_MemRegion(mrd);
      }
      // Reset the dirty window, while continuing to look
      // for the next dirty card that will start a
      // new dirty window.
      end_of_non_clean = cur_hw;
      start_of_non_clean = cur_hw;
    }
    // Note that "cur_entry" leads "start_of_non_clean" in
    // its leftward excursion after this point
    // in the loop and, when we hit the left end of "mr",
    // will point off of the left end of the card-table
    // for "mr".
    cur_entry--;
  }
  // If the first card of "mr" was dirty, we will have
  // been left with a dirty window, co-initial with "mr",
  // which we now process.
  if (start_of_non_clean < end_of_non_clean) {
    const MemRegion mrd(start_of_non_clean, end_of_non_clean);
    _dirty_card_closure->do_MemRegion(mrd);
  }
}