+
+ /*
+ * Announced bit length of d[] will be the sum of the announced
+ * bit lengths of a[] and b[]; but the lengths are encoded.
+ */
+ dl = (a[0] & 15) + (d[0] & 15);
+ dh = (a[0] >> 4) + (b[0] >> 4);
+ d[0] = (dh << 4) + dl + (~(uint16_t)(dl - 15) >> 15);
+