VM_Word mask = VM_Word.fromIntZeroExtend(BUFFER_SIZE - 1); return buf.toWord().and(mask).toOffset();
return buf.toWord().and(BUFFER_MASK).toOffset();
  protected final VM_Offset bufferOffset(VM_Address buf) throws VM_PragmaInline {    VM_Word mask = VM_Word.fromIntZeroExtend(BUFFER_SIZE - 1);    return buf.toWord().and(mask).toOffset();  }