UNION_HASH
val = UNION_HASH(un->un_uppervp, un->un_lowervp);
int ohash = UNION_HASH(un->un_uppervp, un->un_lowervp);
int nhash = UNION_HASH(un->un_uppervp, lowervp);
int ohash = UNION_HASH(un->un_uppervp, un->un_lowervp);
int nhash = UNION_HASH(uppervp, un->un_lowervp);
hash[0] = UNION_HASH(uppervp, lowervp);
hash[1] = UNION_HASH(uppervp, NULLVP);
hash[2] = UNION_HASH(NULLVP, lowervp);