Efficient radix-3 FHT algorithm

By modifying the conventional decomposition formula for the decimation-in-frequency (DIF) case, a more efficient radix-3 fast Hartley transform(FHT) algorithm has been introduced resulting in a fewer number multiplications. The reduction in the number of multiplications is of the order of 25-30 percent. It is useful in cases where the sequence length is closer to a power of 3 rather than a power of 2.