l_setbit
l_setbit(gch(curr)->marked, FINALIZEDBIT); /* won't be finalized again */
l_setbit(ho->marked, SEPARATED); /* mark it as such */
#define gray2black(x) l_setbit((x)->gch.marked, BLACKBIT)
#define luaS_fix(s) l_setbit((s)->tsv.marked, FIXEDBIT)