Just as for the DFT, evaluating the DHT definition directly would require O("N"2) arithmetical operations (see Big O notation). There are fast algorithms similar to the FFT, however, that compute the same result in only O("N" log "N") operations. Nearly every FFT algorithm, from Cooley–Tukey to prime-factor to Winograd (1985) to Bruun's (1993), has a direct analogue for the discrete Hartley transform. (However, a few of the more exotic FFT algorithms, such as the QFT, have not yet been investigated in the context of the DHT.)