MS_CALC_MARK_BIT (word, bit, obj);
SGEN_ASSERT (9, !MS_MARK_BIT (block, word, bit), "object %p already marked", obj);
MS_SET_MARK_BIT (block, word, bit);
MS_CALC_MARK_BIT (word, bit, obj);
SGEN_ASSERT (9, !MS_MARK_BIT (block, word, bit), "object %p already marked", obj);
MS_SET_MARK_BIT (block, word, bit);