Using number-theoretic transforms instead of discrete Fourier transforms avoids rounding error problems by using modular arithmetic instead of floating-point arithmetic. In order to apply the factoring which enables the FFT to work, the length of the transform must be factorable to small primes and must be a factor of , where "N" is the field size. In particular, calculation using a Galois field GF("k"2), where "k" is a Mersenne prime, allows the use of a transform sized to a power of 2; e.g. supports transform sizes up to 232.