rht_head_hashfn
hash = rht_head_hashfn(ht, tbl, obj, params);
hash = rht_head_hashfn(ht, tbl, obj_old, params);
if (hash != rht_head_hashfn(ht, tbl, obj_new, params))
hash = rht_head_hashfn(ht, tbl, obj, params);
return rht_head_hashfn(ht, tbl, he, ht->p);
hash = rht_head_hashfn(ht, tbl, obj, ht->p);