rtn = ((old & BARRIER_BIT_MASK) == 0); } while(!VM_Interface.attemptAvailableBits(ref, old, old | BARRIER_BIT_MASK)
rtn = old.and(BARRIER_BIT_MASK).isZero(); } while(!VM_Interface.attemptAvailableBits(ref, old, old.or(BARRIER_BIT_MASK))
  static boolean attemptBarrierBitSet(VM_Address ref)    throws VM_PragmaUninterruptible, VM_PragmaInline {    int old = VM_Interface.readAvailableBitsWord(ref);    boolean rtn = ((old & BARRIER_BIT_MASK) == 0);    if (rtn) {      do {        old = VM_Interface.prepareAvailableBits(ref);        rtn = ((old & BARRIER_BIT_MASK) == 0);      } while(!VM_Interface.attemptAvailableBits(ref, old,                                                  old | BARRIER_BIT_MASK)              && rtn);    }    return rtn;  }