-bn_mul_recursive(B<r>, B<a>, B<b>, B<n2>, B<t>) operates on the B<n2>
-word arrays B<a> and B<b> and the 2*B<n2> word arrays B<r> and B<t>.
-B<n2> must be a power of 2. It computes B<a>*B<b> and places the
-result in B<r>.
+bn_mul_recursive(B<r>, B<a>, B<b>, B<n2>, B<dna>, B<dnb>, B<t>) operates
+on the word arrays B<a> and B<b> of length B<n2>+B<dna> and B<n2>+B<dnb>
+(B<dna> and B<dnb> are currently allowed to be 0 or negative) and the 2*B<n2>
+word arrays B<r> and B<t>. B<n2> must be a power of 2. It computes
+B<a>*B<b> and places the result in B<r>.