if (VM.VerifyAssertions) VM.assert((b & ~0x1) == 0);
if (VM.VerifyAssertions) VM._assert((b & ~0x1) == 0);
  void writeMarkBit (Object object, int b) throws VM_PragmaUninterruptible {    if (VM.VerifyAssertions) VM.assert((b & ~0x1) == 0);    if (DEBUG) VM.sysWriteln("writeMarkBit ", VM_Magic.objectAsAddress(object));    int word   = wordIndex(object);    int bitnum = bitIndex(object, word);    int mask   = mask(bitnum);    int newval = b << bitnum;    marks[word] = (marks[word] & mask) | newval;  }