- * Propagate carries. Since the operation above really is a
- * truncature, followed by the addition of nonnegative values,
- * the result will be positive. Moreover, the carry cannot
- * exceed 5 bits (we performed 20 additions with values smaller
- * than 256 bits).
+ * Propagate carries. This is a signed propagation, and the
+ * result may be negative. The loop above may enlarge values,
+ * but not two much: worst case is the chain involving t[i - 3],
+ * in which a value may be added to itself up to 7 times. Since
+ * starting values are 13-bit each, all words fit on 20 bits
+ * (21 to account for the sign bit).