+/* Check if the last non-zero coefficient is bigger that half of the
+ * denominator. If so, we will invert the div to further reduce the number
+ * of distinct divs that may appear.
+ * If the last non-zero coefficient is exactly half the denominator,
+ * then we continue looking for earlier coefficients that are bigger
+ * than half the denominator.
+ */
+static int needs_invert(__isl_keep isl_mat *div, int row)
+{
+ int i;
+ int cmp;
+
+ for (i = div->n_col - 1; i >= 1; --i) {
+ if (isl_int_is_zero(div->row[row][i]))
+ continue;
+ isl_int_mul_ui(div->row[row][i], div->row[row][i], 2);
+ cmp = isl_int_cmp(div->row[row][i], div->row[row][0]);
+ isl_int_divexact_ui(div->row[row][i], div->row[row][i], 2);
+ if (cmp)
+ return cmp > 0;
+ if (i == 1)
+ return 1;
+ }
+
+ return 0;
+}
+
+/* Replace div "div" q = [e/d] by -[(-e+(d-1))/d].
+ * We only invert the coefficients of e (and the coefficient of q in
+ * later divs and in "aff"). After calling this function, the
+ * coefficients of e should be reduced again.
+ */
+static void invert_div(__isl_keep isl_qpolynomial *qp, int div,
+ __isl_keep isl_vec *aff)
+{
+ unsigned total = qp->div->n_col - qp->div->n_row - 2;
+
+ isl_seq_neg(qp->div->row[div] + 1,
+ qp->div->row[div] + 1, qp->div->n_col - 1);
+ isl_int_sub_ui(qp->div->row[div][1], qp->div->row[div][1], 1);
+ isl_int_add(qp->div->row[div][1],
+ qp->div->row[div][1], qp->div->row[div][0]);
+ if (!isl_int_is_zero(aff->el[1 + total + div]))
+ isl_int_neg(aff->el[1 + total + div], aff->el[1 + total + div]);
+ isl_mat_col_mul(qp->div, 2 + total + div,
+ qp->div->ctx->negone, 2 + total + div);
+}
+
+/* Assuming "qp" is a monomial, reduce all its divs to have coefficients
+ * in the interval [0, d-1], with d the denominator and such that the
+ * last non-zero coefficient that is not equal to d/2 is smaller than d/2.
+ *
+ * After the reduction, some divs may have become redundant or identical,
+ * so we call substitute_non_divs and sort_divs. If these functions
+ * eliminate divs or merge two or more divs into one, the coefficients
+ * of the enclosing divs may have to be reduced again, so we call
+ * ourselves recursively if the number of divs decreases.
+ */
+static __isl_give isl_qpolynomial *reduce_divs(__isl_take isl_qpolynomial *qp)
+{
+ int i;
+ isl_vec *aff = NULL;
+ struct isl_upoly *s;
+ unsigned n_div;
+
+ if (!qp)
+ return NULL;
+
+ aff = isl_vec_alloc(qp->div->ctx, qp->div->n_col - 1);
+ aff = isl_vec_clr(aff);
+ if (!aff)
+ goto error;
+
+ isl_int_set_si(aff->el[1 + qp->upoly->var], 1);
+
+ for (i = 0; i < qp->div->n_row; ++i) {
+ normalize_div(qp, i);
+ reduce_div(qp, i, aff);
+ if (needs_invert(qp->div, i)) {
+ invert_div(qp, i, aff);
+ reduce_div(qp, i, aff);
+ }
+ }
+
+ s = isl_upoly_from_affine(qp->div->ctx, aff->el,
+ qp->div->ctx->one, aff->size);
+ qp->upoly = isl_upoly_subs(qp->upoly, qp->upoly->var, 1, &s);
+ isl_upoly_free(s);
+ if (!qp->upoly)
+ goto error;
+
+ isl_vec_free(aff);
+
+ n_div = qp->div->n_row;
+ qp = substitute_non_divs(qp);
+ qp = sort_divs(qp);
+ if (qp && qp->div->n_row < n_div)
+ return reduce_divs(qp);
+
+ return qp;
+error:
+ isl_qpolynomial_free(qp);
+ isl_vec_free(aff);
+ return NULL;
+}
+
+__isl_give isl_qpolynomial *isl_qpolynomial_rat_cst_on_domain(
+ __isl_take isl_space *dim, const isl_int n, const isl_int d)