VM_Word mask = VM_Word.fromIntZeroExtend(BUFFER_SIZE - 1).not(); return buf.toWord().and(mask).toAddress();
return buf.toWord().and(BUFFER_MASK.not()).toAddress();
  protected final VM_Address bufferStart(VM_Address buf) throws VM_PragmaInline {    VM_Word mask = VM_Word.fromIntZeroExtend(BUFFER_SIZE - 1).not();    return buf.toWord().and(mask).toAddress();  }