大O符号
The Schönhage–Strassen algorithm is an asymptotically fast multiplication algorithm for large integers. It was developed by Arnold Schönhage and Volker Strassen in 1971. The run-time bit complexity is, in Big O notation, formula_1 for two "n"-digit numbers. The algorithm uses recursive Fast Fourier transforms in rings with 2"n"+1 elements, a specific type of number theoretic transform.