I like the fast fourier transform method for fast integer multiplication. Only applicable on really big inputs, but the idea is that it computes the fft of both integers, does point-wise multiplication of the resulting vectors, then does the inverse fft to recover the product. More about this (<a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Multiplication_algorithm#Fourier_transform_methods" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Multiplication_algorithm#Fouri...</a>).<p>Another interesting but asymptotically slower integer&#x2F;polynomial multiplication algorithm is Karatsuba&#x27;s.