for (i = 0; i < ib1->n_elems * ib1->id_size; i++)
ib1->idsum[i] ^= ib2->idsum[i];
for (i = 0; i < ib1->n_elems; i++) {
ib1->count[i] -= ib2->count[i];
for (i = 0; i < ib1->n_elems * ib1->id_size; i++)
ib1->idsum[i] ^= ib2->idsum[i];
for (i = 0; i < ib1->n_elems; i++) {
ib1->count[i] -= ib2->count[i];