OpenJDK GC patch, modified 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;
      
      cur_entry--;
    } 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);
      }
      
      // fast forward via continuous range of clean cards
      // hardcoded 64 bit version
      if ((((jlong)cur_entry) & 7) == 0) {
          jbyte* cur_row = cur_entry - 8;
          while(cur_row >= limit) {
            if (*((jlong*)cur_row) == ((jlong)-1) /* hardcoded row of 8 clean cards */) {
                  cur_row -= 8;
              }
              else {                  
                  break;
              }
          }
          cur_entry = cur_row + 7;
          HeapWord* last_hw = _ct->addr_for(cur_row + 8);
          end_of_non_clean = last_hw;
          start_of_non_clean = last_hw;
      }
      else {
          // 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;
          cur_entry--;
      }
    }
    // 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".
  }
  // 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);
  }
}