zeroSmall(start, len);
zeroSmall(start, bytes);
  public static void zero(Address start, Extent len) throws InlinePragma {    if (Assert.VERIFY_ASSERTIONS)      Assert._assert((len.toInt() & (BYTES_IN_WORD-1)) == 0                     && (start.toInt() & (BYTES_IN_WORD-1)) == 0);    if (len.GT(Extent.fromIntZeroExtend(256)))       org.mmtk.vm.Memory.zero(start, len);    else      zeroSmall(start, len);  }