+/*
+ * Compute the slice size of the next group.
+ *
+ * The FEC parameters n and k are fixed but the slice size varies per
+ * FEC group. We'd like to choose slices as small as possible to avoid
+ * unnecessary FEC calculations but large enough to guarantee that the
+ * k data slices suffice to encode the header (if needed) and the data
+ * chunk(s).
+ *
+ * Once we know the payload of the next group, we define the number s
+ * of bytes per slice for this group by
+ *
+ * s = ceil(payload / k)
+ *
+ * However, for header streams, computing s is more complicated since no
+ * overlapping of header and data slices is possible. Hence we have k >=
+ * 2 and s must satisfy
+ *
+ * (*) ceil(h / s) + ceil(d / s) <= k
+ *
+ * where h and d are payload of the header and the data chunk(s)
+ * respectively. In general there is no value for s such that (*)
+ * becomes an equality, for example if h = 4000, d = 5000 and k = 10.
+ *
+ * We use the following approach for computing a suitable value for s:
+ *
+ * Let
+ * k1 := ceil(k * min(h, d) / (h + d)),
+ * k2 := k - k1.
+ *
+ * Note that k >= 2 implies k1 > 0 and k2 > 0, so
+ *
+ * s := max(ceil(min(h, d) / k1), ceil(max(h, d) / k2))
+ *
+ * is well-defined. Inequality (*) holds for this value of s since k1
+ * slices suffice to store min(h, d) while k2 slices suffice to store
+ * max(h, d), i.e. the first addent of (*) is bounded by k1 and the
+ * second by k2.
+ *
+ * For the above example we obtain
+ *
+ * k1 = ceil(10 * 4000 / 9000) = 5, k2 = 5,
+ * s = max(4000 / 5, 5000 / 5) = 1000,
+ *
+ * which is optimal since a slice size of 999 bytes would already require
+ * 11 slices.
+ */
+static int compute_slice_size(struct fec_client *fc, struct vss_task *vsst)
+{
+ struct fec_group *g = &fc->group;
+ int k = fc->fcp->data_slices_per_group + fc->num_extra_slices;
+ int n = fc->fcp->slices_per_group + fc->num_extra_slices;
+ int ret, k1, k2, h, d, min, max, sum;
+ int max_slice_bytes = fc->mps - FEC_HEADER_SIZE;
+ int max_group_bytes;
+
+ if (!need_audio_header(fc, vsst)) {
+ max_group_bytes = k * max_slice_bytes;
+ g->num_header_slices = 0;
+ ret = compute_group_size(vsst, g, max_group_bytes);