prev = block;
  final static int sanityTraverse(Address block, Address prev,                                    boolean verbose) {    if (verbose) Log.write("[");    boolean first = true;    int blocks = 0;    while (!block.isZero()) {      if (Assert.VERIFY_ASSERTIONS) Assert._assert(getPrevBlock(block).EQ(prev));      blocks++;      if (verbose) {        if (!first)          Log.write(" ");        else          first = false;        Log.write(block);      }      prev = block;      block = getNextBlock(block);      Log.flush();    }    if (verbose) Log.write("]");    return blocks;  }